On 26/09/2026 11:11, Carlos E.R. wrote:
On 2026-09-25 21:39, J. P. Gilliver wrote:
On 2026/9/25 0:17:41, Charlie Gibbs wrote:...
On 2026-09-24, J. P. Gilliver <G6JPG@255soft.uk> wrote:[]
(Cable _radio_ did have some reach, I think in the 1950s; I'm not sure
about this, but I _think_ that was basically a big radio (wireless) set
at the hub, with just direct audio distributed. Not sure how channel
selection was implemented! "Rediffusion" was I think the main company.)
I had not heard of cable radio. Interesting.
I asked GoogleAI:However, radio over a phone line, yes. Still exists here, usually hired
by commercial sites. I assume that now it uses internet.
I asked ChatGPT: it was called "Hilo musical" (musical wire or thread),
a Telef||nica service. Currently it is named "Spotmusic". Different
technology.
The old one transmitted 6 channels on the same copper pair used for the
phone, at a higher frequency. Somewhat similar to ADSL.
and it seems like only 60 years ago that we had "Dial a Disc" ...
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the >Windows and Linux ones next time.
On 2026/9/26 11:47:1, Abandoned Trolley wrote:
On 26/09/2026 11:11, Carlos E.R. wrote:
On 2026-09-25 21:39, J. P. Gilliver wrote:
On 2026/9/25 0:17:41, Charlie Gibbs wrote:...
On 2026-09-24, J. P. Gilliver <G6JPG@255soft.uk> wrote:[]
I had not heard of cable radio. Interesting.
(Cable _radio_ did have some reach, I think in the 1950s; I'm not sure >>>> about this, but I _think_ that was basically a big radio (wireless) set >>>> at the hub, with just direct audio distributed. Not sure how channel
selection was implemented! "Rediffusion" was I think the main company.) >>>
I don't think it was called that.>>
I asked GoogleAI:However, radio over a phone line, yes. Still exists here, usually hired >>> by commercial sites. I assume that now it uses internet.
I asked ChatGPT: it was called "Hilo musical" (musical wire or thread), >>> a Telef<nica service. Currently it is named "Spotmusic". Different
technology.
The old one transmitted 6 channels on the same copper pair used for the >>> phone, at a higher frequency. Somewhat similar to ADSL.
Yes, Rediffusion originally started in the UK by relaying radio
broadcasts directly to subscribers' homes over wired networks.
How the Radio Relay Worked
o Wired Distribution: Founded as Broadcast Relay Service Limited (later
named Rediffusion) in 1928, the company used physical cables to pipe
radio programs straight into houses.
o No Radio Set Needed: Subscribers did not need an expensive or
complicated wireless radio receiver; they only needed a simple
loudspeaker and a selector switch wired to the Rediffusion network.
o Clear Reception: The wired "pipe radio" system eliminated static,
fading, and interference common with early aerial radio transmissions.
o BBC and Local Feeds: The service provided crisp audio relays of BBC
radio programmes and other stations from the early 1930s onwards, long
before the company expanded into television rental and commercial >broadcasting.
The standard Rediffusion selector box was a purely mechanical,
multi-position rotary switch that didn't require any mains electricity
or batteries to function.
?? How the Box Operated
o Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV) signals
over the air via high-quality aerials.
o Multi-Core Cables: The amplified signals were sent out down the street >using overhead cables that contained multiple separate wires (cores).
Each core carried a different station or channel.
o The Rotary Switch: The selector box in your living room was connected
to this incoming multi-core cable. When you turned the dial, it
physically moved a brass contact inside the box to connect your speaker
to a specific pair of wires inside the cable.
o Volume Control: The box also housed a simple variable resistor >(potentiometer). Turning the volume knob restricted or allowed more >electrical current to flow to the speaker, making the audio quieter or >louder.Because the central station did all the heavy lifting of
capturing and amplifying the signal, the box in the home was effectively
just a remote switch and volume knob for a giant, town-wide audio system.>> >So there you have it! It was as I thought - just audio distribution; not
even carrier.>
and it seems like only 60 years ago that we had "Dial a Disc" ...
I'm pretty surer that continued until at least the 1970s ...
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the Windows and Linux ones next time.
On 2026/9/26 11:47:1, Abandoned Trolley wrote:[...]
On 26/09/2026 11:11, Carlos E.R. wrote:
I had not heard of cable radio. Interesting.
I don't think it was called that.>>
On Sat, 26 Sep 2026 19:08:02 +0100, "J. P. Gilliver"I have set followup. Thanks for your patience, Windows and Linux folk!>>
<G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the
Windows and Linux ones next time.
[]On 2026/9/26 11:47:1, Abandoned Trolley wrote:
On 26/09/2026 11:11, Carlos E.R. wrote:
On 2026-09-25 21:39, J. P. Gilliver wrote:
On 2026/9/25 0:17:41, Charlie Gibbs wrote:
[]I had not heard of cable radio. Interesting.
I don't think it was called that.>>
[]I asked GoogleAI:
Yes, Rediffusion originally started in the UK by relaying radio
broadcasts directly to subscribers' homes over wired networks.
How the Radio Relay Worked
rCo Wired Distribution: Founded as Broadcast Relay Service Limited (later
named Rediffusion) in 1928, the company used physical cables to pipe
radio programs straight into houses.
Where did Rediffusion get the signal from given that there was no FMI think, basically, they had a big, sensitive, wireless set at the shop, connected to good (and possibly directional) aerials - better than the
in the 1930s? How did they eliminate static, fading, and interference especially if the conurbation was a long distance from the
transmitter?
I believe the system continued in the Falkland Islands until the lateI asked Google "Did the Falkland Islands have an unusual radio
1980s but I cannot find any details. Does anyone know?
J. P. Gilliver <G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the
Windows and Linux ones next time.
Please don't do that, unless it's really *only* UK *and* broadcast
related.
On 2026/9/26 20:10:13, Frank Slootweg wrote:Oops, sorry, I thought I was replying to our .nl friend.
J. P. Gilliver <G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the >>> Windows and Linux ones next time.
Please don't do that, unless it's really *only* UK *and* broadcast
related.
I suggest you take that 'group; they're friendly, and from your posts I> think you'd fit right in with the atmosphere there. Although, obviously,
it mostly discusses UK matters, it does cover others (recent discussions about long wave stations for example).
[]
" To reach remote, rural sheep farms in the
countryside (known locally as the "Camp"), the audio feed was patched
into the existing overland telephone wire network during the evenings."; "This unique setup served as a vital lifeline, delivering BBC news
updates, government announcements, and local music. Remarkably, despite wireless AM transmissions being introduced in the 1940s and 1950s, "The
Box" was so reliable and deeply woven into local culture that the wired infrastructure remained in active use through the 1982 Falklands War.
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the Windows and Linux ones next time.
On 2026/9/26 11:47:1, Abandoned Trolley wrote:
On 26/09/2026 11:11, Carlos E.R. wrote:
On 2026-09-25 21:39, J. P. Gilliver wrote:
(Cable _radio_ did have some reach, I think in the 1950s; I'm not sure >>>> about this, but I _think_ that was basically a big radio (wireless) set >>>> at the hub, with just direct audio distributed. Not sure how channelI had not heard of cable radio. Interesting.
selection was implemented! "Rediffusion" was I think the main company.) >>>
I don't think it was called that.>>
I asked GoogleAI:However, radio over a phone line, yes. Still exists here, usually hired
by commercial sites. I assume that now it uses internet.
I asked ChatGPT: it was called "Hilo musical" (musical wire or thread),
a Telef||nica service. Currently it is named "Spotmusic". Different
technology.
The old one transmitted 6 channels on the same copper pair used for the
phone, at a higher frequency. Somewhat similar to ADSL.
Yes, Rediffusion originally started in the UK by relaying radio
broadcasts directly to subscribers' homes over wired networks.
How the Radio Relay Worked
rCo Wired Distribution: Founded as Broadcast Relay Service Limited (later named Rediffusion) in 1928, the company used physical cables to pipe
radio programs straight into houses.
rCo No Radio Set Needed: Subscribers did not need an expensive or
complicated wireless radio receiver; they only needed a simple
loudspeaker and a selector switch wired to the Rediffusion network.
rCo Clear Reception: The wired "pipe radio" system eliminated static,
fading, and interference common with early aerial radio transmissions.
rCo BBC and Local Feeds: The service provided crisp audio relays of BBC
radio programmes and other stations from the early 1930s onwards, long
before the company expanded into television rental and commercial broadcasting.
The standard Rediffusion selector box was a purely mechanical,
multi-position rotary switch that didn't require any mains electricity
or batteries to function.
rUON+A How the Box Operated
rCo Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV) signals
over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the street using overhead cables that contained multiple separate wires (cores).
Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was connected
to this incoming multi-core cable. When you turned the dial, it
physically moved a brass contact inside the box to connect your speaker
to a specific pair of wires inside the cable.
rCo Volume Control: The box also housed a simple variable resistor (potentiometer). Turning the volume knob restricted or allowed more electrical current to flow to the speaker, making the audio quieter or louder.Because the central station did all the heavy lifting of
capturing and amplifying the signal, the box in the home was effectively
just a remote switch and volume knob for a giant, town-wide audio system.>> So there you have it! It was as I thought - just audio distribution; not
even carrier.>
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the Windows and Linux ones next time.
On 2026/9/26 11:47:1, Abandoned Trolley wrote:
On 26/09/2026 11:11, Carlos E.R. wrote:
On 2026-09-25 21:39, J. P. Gilliver wrote:
On 2026/9/25 0:17:41, Charlie Gibbs wrote:...
On 2026-09-24, J. P. Gilliver <G6JPG@255soft.uk> wrote:[]
I had not heard of cable radio. Interesting.
(Cable _radio_ did have some reach, I think in the 1950s; I'm not sure >>>> about this, but I _think_ that was basically a big radio (wireless) set >>>> at the hub, with just direct audio distributed. Not sure how channel
selection was implemented! "Rediffusion" was I think the main company.) >>>
I don't think it was called that.>>
I asked GoogleAI:However, radio over a phone line, yes. Still exists here, usually hired
by commercial sites. I assume that now it uses internet.
I asked ChatGPT: it was called "Hilo musical" (musical wire or thread),
a Telef||nica service. Currently it is named "Spotmusic". Different
technology.
The old one transmitted 6 channels on the same copper pair used for the
phone, at a higher frequency. Somewhat similar to ADSL.
Yes, Rediffusion originally started in the UK by relaying radio
broadcasts directly to subscribers' homes over wired networks.
How the Radio Relay Worked
rCo Wired Distribution: Founded as Broadcast Relay Service Limited (later named Rediffusion) in 1928, the company used physical cables to pipe
radio programs straight into houses.
rCo No Radio Set Needed: Subscribers did not need an expensive or
complicated wireless radio receiver; they only needed a simple
loudspeaker and a selector switch wired to the Rediffusion network.
rCo Clear Reception: The wired "pipe radio" system eliminated static,
fading, and interference common with early aerial radio transmissions.
rCo BBC and Local Feeds: The service provided crisp audio relays of BBC
radio programmes and other stations from the early 1930s onwards, long
before the company expanded into television rental and commercial broadcasting.
The standard Rediffusion selector box was a purely mechanical,
multi-position rotary switch that didn't require any mains electricity
or batteries to function.
rUON+A How the Box Operated
rCo Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV) signals
over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the street using overhead cables that contained multiple separate wires (cores).
Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was connected
to this incoming multi-core cable. When you turned the dial, it
physically moved a brass contact inside the box to connect your speaker
to a specific pair of wires inside the cable.
rCo Volume Control: The box also housed a simple variable resistor (potentiometer). Turning the volume knob restricted or allowed more electrical current to flow to the speaker, making the audio quieter or louder.Because the central station did all the heavy lifting of
capturing and amplifying the signal, the box in the home was effectively
just a remote switch and volume knob for a giant, town-wide audio system.>> So there you have it! It was as I thought - just audio distribution; not
even carrier.>
and it seems like only 60 years ago that we had "Dial a Disc" ...
I'm pretty surer that continued until at least the 1970s ...
But isn't 'wire' a form of 'cable'??
On 27/09/2026 10:58, Daniel70 wrote:
But isn't 'wire' a form of 'cable'??
In *this* context cable was coaxial RF, wire tended to me more twisted pair
On 26/09/2026 19:08, J. P. Gilliver wrote:[]
rUON+A How the Box OperatedAt some point, Rediffusion added TV: BBC1, BBC2 and ITV. The TV sets
rCo Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV) signals
over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the street >> using overhead cables that contained multiple separate wires (cores).
Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was connected
were simplified, as there was no tuner (or carrier I suppose). And the
TVs could also receive radio (without the TV being powered up).
On 2026/9/27 11:44:52, Max Demian wrote:
On 26/09/2026 19:08, J. P. Gilliver wrote:[]
rUON+A How the Box Operated
rCo Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV) signals >>> over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the street >>> using overhead cables that contained multiple separate wires (cores).
Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was connected
At some point, Rediffusion added TV: BBC1, BBC2 and ITV. The TV sets
were simplified, as there was no tuner (or carrier I suppose). And the
TVs could also receive radio (without the TV being powered up).
So when the switch was in the radio position (one of several), the
incoming signal was routed directly to the TV speaker?
J. P. Gilliver wrote:Student housing where I lived in the 80s still had the chunky
Max Demian wrote:
At some point, Rediffusion added TV: BBC1, BBC2 and ITV. The TV sets
were simplified, as there was no tuner (or carrier I suppose). And the
TVs could also receive radio (without the TV being powered up).
So when the switch was in the radio position (one of several), the
incoming signal was routed directly to the TV speaker?
That's right.
On 27/09/2026 16:12, J. P. Gilliver wrote:
On 2026/9/27 11:44:52, Max Demian wrote:
On 26/09/2026 19:08, J. P. Gilliver wrote:[]
rUON+A How the Box Operated
rCo Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV)
signals
over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the
street
using overhead cables that contained multiple separate wires (cores).
Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was connected
At some point, Rediffusion added TV: BBC1, BBC2 and ITV. The TV sets
were simplified, as there was no tuner (or carrier I suppose). And the
TVs could also receive radio (without the TV being powered up).
So when the switch was in the radio position (one of several), the
incoming signal was routed directly to the TV speaker?
That's right.
On 2026/9/26 21:2:35, J. P. Gilliver wrote:
On 2026/9/26 20:10:13, Frank Slootweg wrote:
J. P. Gilliver <G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the >>> Windows and Linux ones next time.
Please don't do that, unless it's really *only* UK *and* broadcast
related.
I suggest you take that 'group; they're friendly, and from your posts I think you'd fit right in with the atmosphere there. Although, obviously,Oops, sorry, I thought I was replying to our .nl friend.
it mostly discusses UK matters, it does cover others (recent discussions about long wave stations for example).
[]
" To reach remote, rural sheep farms in the
countryside (known locally as the "Camp"), the audio feed was patched
into the existing overland telephone wire network during the evenings."
On 27/09/2026 18:12, Max Demian wrote:
On 27/09/2026 16:12, J. P. Gilliver wrote:Probably not directly: Normally the audio would be 100V line and need an impedance matching transformer (or maybe the TV sets output transformer
On 2026/9/27 11:44:52, Max Demian wrote:
On 26/09/2026 19:08, J. P. Gilliver wrote:[]
rUON+A How the Box Operated
rCo Central Distribution: Rediffusion set up central amplification
stations in towns. These stations received radio (and later, TV)
signals
over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the >>>>> street
using overhead cables that contained multiple separate wires (cores). >>>>> Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was
connected
At some point, Rediffusion added TV: BBC1, BBC2 and ITV. The TV sets >>>> were simplified, as there was no tuner (or carrier I suppose). And the >>>> TVs could also receive radio (without the TV being powered up).
So when the switch was in the radio position (one of several), the
incoming signal was routed directly to the TV speaker?
That's right.
via a different tap)
On 27/09/2026 18:34, The Natural Philosopher wrote:
On 27/09/2026 18:12, Max Demian wrote:
On 27/09/2026 16:12, J. P. Gilliver wrote:Probably not directly: Normally the audio would be 100V line and need an impedance matching transformer (or maybe the TV sets output transformer
On 2026/9/27 11:44:52, Max Demian wrote:
On 26/09/2026 19:08, J. P. Gilliver wrote:[]
rUON+A How the Box Operated
rCo Central Distribution: Rediffusion set up central amplification >>>>> stations in towns. These stations received radio (and later, TV)
signals
over the air via high-quality aerials.
rCo Multi-Core Cables: The amplified signals were sent out down the >>>>> street
using overhead cables that contained multiple separate wires (cores). >>>>> Each core carried a different station or channel.
rCo The Rotary Switch: The selector box in your living room was
connected
At some point, Rediffusion added TV: BBC1, BBC2 and ITV. The TV sets >>>> were simplified, as there was no tuner (or carrier I suppose). And the >>>> TVs could also receive radio (without the TV being powered up).
So when the switch was in the radio position (one of several), the
incoming signal was routed directly to the TV speaker?
That's right.
via a different tap)
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket of
the main (valve) radio so you could listen in the kitchen. I had one
which had a transformer and a wander plug arrangement so you could match
it. Some valve radios had a high impedance output, so presumably both connections would be at (more or less) HT voltage above the radio
chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
J. P. Gilliver <G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the
Windows and Linux ones next time.
Please don't do that, unless it's really *only* UK *and* broadcast related.
On 2026/9/26 11:47:1, Abandoned Trolley wrote:[...]
On 26/09/2026 11:11, Carlos E.R. wrote:
I had not heard of cable radio. Interesting.
I don't think it was called that.>>
In The Netherlands, it was called 'draadomroep', which roughly
translates to wirebroadcast, so 'wire', not 'cable' and 'broadcast', not 'radio' (because it wasn't).
And it indeed worked like (your snipped) Google's AI Overview said.
[...]
J. P. Gilliver <G6JPG@255soft.uk> wrote:
On 2026/9/26 21:2:35, J. P. Gilliver wrote:
On 2026/9/26 20:10:13, Frank Slootweg wrote:Oops, sorry, I thought I was replying to our .nl friend.
J. P. Gilliver <G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the >>>>> Windows and Linux ones next time.
Please don't do that, unless it's really *only* UK *and* broadcast
related.
I suggest you take that 'group; they're friendly, and from your posts I
think you'd fit right in with the atmosphere there. Although, obviously, >>> it mostly discusses UK matters, it does cover others (recent discussions >>> about long wave stations for example).
[]
Well, I don't know if I am your (singular and plural) friend, but I
*do* live in NL! :-)
On 2026/9/27 19:20:49, Frank Slootweg wrote:
J. P. Gilliver <G6JPG@255soft.uk> wrote:
On 2026/9/26 21:2:35, J. P. Gilliver wrote:
On 2026/9/26 20:10:13, Frank Slootweg wrote:Oops, sorry, I thought I was replying to our .nl friend.
J. P. Gilliver <G6JPG@255soft.uk> wrote:
uk.tech.broadcast added, as it seemed appropriate! I'll maybe remove the
Windows and Linux ones next time.
Please don't do that, unless it's really *only* UK *and* broadcast >>>> related.
I suggest you take that 'group; they're friendly, and from your posts I >>> think you'd fit right in with the atmosphere there. Although, obviously, >>> it mostly discusses UK matters, it does cover others (recent discussions >>> about long wave stations for example).
[]
Well, I don't know if I am your (singular and plural) friend, but I
*do* live in NL! :-)
I meant Jan Panteltje. But you'd probably enjoy (and be welcome in) UYB too.
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket of
the main (valve) radio so you could listen in the kitchen. I had one
which had a transformer and a wander plug arrangement so you could match
it. Some valve radios had a high impedance output, so presumably both connections would be at (more or less) HT voltage above the radio
chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer.
J. P. Gilliver. UMRA: 1960/<1985 MB++G()ALIS-Ch++(p)Ar++T+H+Sh0!:`)DNAf
The web is a blank slate; you can't design technology that is 'good'.
You can't design paper that you can only write good things on. There
are no good or evil tools. You can put an engine in an ambulance or a
tank. - Sir Tim Berners-Lee, Radio Times 2009-Jan-30 to -Feb-5.
J. P. Gilliver. UMRA: 1960/<1985 MB++G()ALIS-Ch++(p)Ar++T+H+Sh0!:`)DNAf
The web is a blank slate; you can't design technology that is 'good'.
You can't design paper that you can only write good things on. There
are no good or evil tools. You can put an engine in an ambulance or a
tank. - Sir Tim Berners-Lee, Radio Times 2009-Jan-30 to -Feb-5.
A power so great it can only be used for good or evil!
-- Firesign Theatre
On 28/09/2026 17:30, Charlie Gibbs wrote:
Forward! Into the Past!J. P. Gilliver. UMRA: 1960/<1985 MB++G()ALIS-Ch++(p)Ar++T+H+Sh0!:`)DNAf
The web is a blank slate; you can't design technology that is 'good'.
You can't design paper that you can only write good things on. There
are no good or evil tools. You can put an engine in an ambulance or a
tank. - Sir Tim Berners-Lee, Radio Times 2009-Jan-30 to -Feb-5.
A power so great it can only be used for good or evil!
-- Firesign Theatre
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could
match it. Some valve radios had a high impedance output, so presumably
both connections would be at (more or less) HT voltage above the radio
chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you
could match it. Some valve radios had a high impedance output, so
presumably both connections would be at (more or less) HT voltage
above the radio chassis (which would be earth if the earth socket was
connected). I think there were high impedance horn extension speakers
at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could
match it. Some valve radios had a high impedance output, so presumably
both connections would be at (more or less) HT voltage above the radio
chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
On 29/09/2026 12:01, Max Demian wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you
could match it. Some valve radios had a high impedance output, so
presumably both connections would be at (more or less) HT voltage
above the radio chassis (which would be earth if the earth socket was
connected). I think there were high impedance horn extension speakers
at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot build a
valve amplifier that delivers true AC without an isolation transformer.
Loudspeakers don't like DC bias
On 29/09/2026 12:01, Max Demian wrote:[]
(Yes, I had - still have, somewhere - such headphones from when I wasI think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot build a
valve amplifier that delivers true AC without an isolation transformer. Loudspeakers don't like DC bias
On 2026/9/28 17:46:5, The Natural Philosopher wrote:
On 28/09/2026 17:30, Charlie Gibbs wrote:
Forward! Into the Past!J. P. Gilliver. UMRA: 1960/<1985 MB++G()ALIS-Ch++(p)Ar++T+H+Sh0!:`)DNAf >>>>
The web is a blank slate; you can't design technology that is 'good'.
You can't design paper that you can only write good things on. There
are no good or evil tools. You can put an engine in an ambulance or a
tank. - Sir Tim Berners-Lee, Radio Times 2009-Jan-30 to -Feb-5.
A power so great it can only be used for good or evil!
-- Firesign Theatre
It's so simple,
so very simple,
that only
a child
can do it!
(Tom Lehrer, "New Math".)
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot build a
valve amplifier that delivers true AC without an isolation transformer. Loudspeakers don't like DC bias
Max Demian <max_demian@bigfoot.com>wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could
match it. Some valve radios had a high impedance output, so presumably
both connections would be at (more or less) HT voltage above the radio
chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
On 28/09/2026 22:25, J. P. Gilliver wrote:[]
It's so simple,
so very simple,
that only
a child
can do it!
(Tom Lehrer, "New Math".)
"Base eight is just like base ten really - if you're missing two fingers!"
A fellow Lehrer fan. I first heard his work when I was working in a chemistry lab in my year off before university, and my supervisor and I
got onto the subject of small, imprecise units of measurement: jots, smidgens and pinches.
And Tony sang "It just takes a smidgen / To poison a pigeon" and the
conversation lurched off sideways into the works of Tom Lehrer. He lent
me a tape he'd made of a couple of his TL LPs. And the rest is history.
I've yet to meet a Henry who spells his name "Hen3ry (the 3 is silent)"
but I did know a woman at university called Matilda who went one better
and signed her name "Ma~" (ma-tilde) which I'm sure TL would have
approved of.
On 29/09/2026 13:05, The Natural Philosopher wrote:
Its NOT juts a matter of impedance - its a matter of DC bias. You
cannot build a
valve amplifier that delivers true AC without an isolation
transformer. Loudspeakers don't like DC bias
Can't you feed the loudspeaker via an electrolitic capacitor to stop the
DC?
Max Demian <max_demian@bigfoot.com>wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could >>>> match it. Some valve radios had a high impedance output, so presumably >>>> both connections would be at (more or less) HT voltage above the radio >>>> chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Yes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
Keeping the subject line relevant is a full-time job in this thread, let alone any chance of the body being on-topic (in now 5 'groups)!
On 2026/9/29 16:40:21, NY wrote:
A fellow Lehrer fan. I first heard his work when I was working in a
chemistry lab in my year off before university, and my supervisor and I
So not The Elements, then!
got onto the subject of small, imprecise units of measurement: jots,
smidgens and pinches.
And Tony sang "It just takes a smidgen / To poison a pigeon" and the
Have you come across the orchestrated version? IMO beautifully done (I
don't know by whom - probably himself): https://www.youtube.com/watch?v=wsMLDzlAm_A .
Nice story about that which I _hope_ is true - the orchestral sheet
music parts had been handed out, but _without_ the title; little
mutterings from the orchestra of "what a charming little waltz" (which
it is) - then the producer tapped and said "OK - Poisoning Pigeons in
the Park, take one", to a general dropping of jaws.
conversation lurched off sideways into the works of Tom Lehrer. He lent
me a tape he'd made of a couple of his TL LPs. And the rest is history.
Did you know he'd _specifically_ made his works - including recordings - public domain? Nice man.
I've yet to meet a Henry who spells his name "Hen3ry (the 3 is silent)"
The delivery is excellent there: At first you're supposed to think it's Henrrry, until he adds that line.
but I did know a woman at university called Matilda who went one better
and signed her name "Ma~" (ma-tilde) which I'm sure TL would have
approved of.
Lovely!
On 2026-09-29, J. P. Gilliver <G6JPG@255soft.uk> wrote:
Keeping the subject line relevant is a full-time job in this thread, let
alone any chance of the body being on-topic (in now 5 'groups)!
On 2026/9/29 16:40:21, NY wrote:
A fellow Lehrer fan. I first heard his work when I was working in a
chemistry lab in my year off before university, and my supervisor and I
So not The Elements, then!
Still, nobody could torture a rhyme like Tom Lehrer:
These are the only ones of which the news has come to Hah-vahd.
And there may be many others but they haven't been discah-vahd.
I never heard him rhyme "orange". Too simple, probably.
got onto the subject of small, imprecise units of measurement: jots,
smidgens and pinches.
And Tony sang "It just takes a smidgen / To poison a pigeon" and the
Have you come across the orchestrated version? IMO beautifully done (I
don't know by whom - probably himself):
https://www.youtube.com/watch?v=wsMLDzlAm_A .
Nice story about that which I _hope_ is true - the orchestral sheet
music parts had been handed out, but _without_ the title; little
mutterings from the orchestra of "what a charming little waltz" (which
it is) - then the producer tapped and said "OK - Poisoning Pigeons in
the Park, take one", to a general dropping of jaws.
Wow. I didn't hear that version.
conversation lurched off sideways into the works of Tom Lehrer. He lent
me a tape he'd made of a couple of his TL LPs. And the rest is history.
Did you know he'd _specifically_ made his works - including recordings -
public domain? Nice man.
I have a book titled "Too Many Songs by Tom Lehrer with Not Enough
Drawings by Ronald Searle". It contains complete lyrics and piano
scores for all his greatest hits.
Still, nobody could torture a rhyme like Tom Lehrer:
These are the only ones of which the news has come to Hah-vahd.
And there may be many others but they haven't been discah-vahd.
On Tue, 29 Sept 2026 19:19, Charlie Gibbs wrote:And the split line-ends:
Still, nobody could torture a rhyme like Tom Lehrer:
-a-a-a-a These are the only ones of which the news has come to Hah-vahd.
-a-a-a-a And there may be many others but they haven't been discah-vahd.
"We'll try to stay serene and calm
When Alabama gets the bomb"
Works perfectly in American.
Have you come across the orchestrated version? IMO beautifully done (I
don't know by whom - probably himself): https://www.youtube.com/watch?v=wsMLDzlAm_A .
Nice story about that which I _hope_ is true - the orchestral sheet
music parts had been handed out, but _without_ the title; little
mutterings from the orchestra of "what a charming little waltz" (which
it is) - then the producer tapped and said "OK - Poisoning Pigeons in
the Park, take one", to a general dropping of jaws.
Did you know he'd _specifically_ made his works - including recordings - public domain? Nice man.
On 2026-09-29, NY <me@privacy.net> wrote:
On 29/09/2026 21:50, Andr|- Coutanche wrote:
On Tue, 29 Sept 2026 19:19, Charlie Gibbs wrote:And the split line-ends:
Still, nobody could torture a rhyme like Tom Lehrer:"We'll try to stay serene and calm
-a-a-a-a These are the only ones of which the news has come to Hah-vahd. >>>> -a-a-a-a And there may be many others but they haven't been discah-vahd. >>>
When Alabama gets the bomb"
Works perfectly in American.
Getting ecstatic
And sorta dramatic
And doing the Vatic-
an Rag
My favourite split is:
And you may have thought it tragic,
Not to mention other adjec-
tives, to think of all the weeping they will do.
Getting ecstatic[]
And sorta dramatic
And doing the Vatic-
an Rag
There the guy who's got religion'll
tell you if your sin's original
On 29/09/2026 21:50, Andr|- Coutanche wrote:
On Tue, 29 Sept 2026 19:19, Charlie Gibbs wrote:And the split line-ends:
Still, nobody could torture a rhyme like Tom Lehrer:
-a-a-a-a These are the only ones of which the news has come to Hah-vahd. >>> -a-a-a-a And there may be many others but they haven't been discah-vahd.
"We'll try to stay serene and calm
When Alabama gets the bomb"
Works perfectly in American.
Getting ecstatic
And sorta dramatic
And doing the Vatic-
an Rag
On 2026-09-29, NY <me@privacy.net> wrote:
On 29/09/2026 21:50, Andr|- Coutanche wrote:
On Tue, 29 Sept 2026 19:19, Charlie Gibbs wrote:And the split line-ends:
Still, nobody could torture a rhyme like Tom Lehrer:"We'll try to stay serene and calm
-a-a-a-a These are the only ones of which the news has come to Hah-vahd. >>>> -a-a-a-a And there may be many others but they haven't been discah-vahd. >>>
When Alabama gets the bomb"
Works perfectly in American.
Getting ecstatic
And sorta dramatic
And doing the Vatic-
an Rag
My favourite split is:
And you may have thought it tragic,
Not to mention other adjec-
tives, to think of all the weeping they will do.
On 29/09/2026 16:53, The Other John wrote:
On 29/09/2026 13:05, The Natural Philosopher wrote:
Its NOT juts a matter of impedance - its a matter of DC bias. You
cannot build a
valve amplifier that delivers true AC without an isolation
transformer. Loudspeakers don't like DC bias
Can't you feed the loudspeaker via an electrolitic capacitor to stop the DC?
No. Because there is no 'PNP' valve you can't make a push pull amplifier
so you are always stuck with having to run a split coil output
transformer, or a class A single winding output transformer. Although it
may be theoretically possible to somehow kludge a class B valve
amplifier using just 'NPN' style valves it is probably going to end up massively more expensive and complex than simply popping in an output transformer.
The same thing happened with early germanium transistors. PNP only, so
we used little transformers. Once NPN became available that was it for transformers
On 29/09/2026 12:01, Max Demian wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same
way that there were boxes you connected to the "extension speaker"
socket of the main (valve) radio so you could listen in the kitchen.
I had one which had a transformer and a wander plug arrangement so
you could match it. Some valve radios had a high impedance output,
so presumably both connections would be at (more or less) HT voltage
above the radio chassis (which would be earth if the earth socket
was connected). I think there were high impedance horn extension
speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't
require a transformer. And, of course, high impedance headphones if
you don't want a loudspeaker.
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot build a
valve amplifier that delivers true AC without an isolation transformer. Loudspeakers don't like DC bias
Max Demian <max_demian@bigfoot.com>wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way
that there were boxes you connected to the "extension speaker" socket
of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could >>>> match it. Some valve radios had a high impedance output, so presumably >>>> both connections would be at (more or less) HT voltage above the radio >>>> chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Yes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
On 2026-09-29 17:54, Jan Panteltje wrote:
Yes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm
speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
I'm not familiar with valves EZ80 and 6CA4, I don't understand the
drawings. :-?
On 30/09/2026 10:27, Carlos E.R. wrote:
On 2026-09-29 17:54, Jan Panteltje wrote:
The EZZ80 and BCA4 valves are full wave rectifiers in the power supply. (Equivalent to two diodes in each valve, with a tapped transformer secondary. Back when semiconductors were expensive, I've done similarYes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm
speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
I'm not familiar with valves EZ80 and 6CA4, I don't understand the
drawings. :-?
with a pair of germanium diodes, as it was cheaper than a bridge
rectifier.)i
The relevant stage for this thread is the output stage, which is two
EL504 pentodes being driven in a sort of push-pull configuration by the
input triode. The EL504s each have an independent DC supply.
The circuit specifies an 800 ohm load, but I first expected to see a
more standard 600 ohm load...
On 2026-09-29 14:05, The Natural Philosopher wrote:
On 29/09/2026 12:01, Max Demian wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same
way that there were boxes you connected to the "extension speaker"
socket of the main (valve) radio so you could listen in the
kitchen. I had one which had a transformer and a wander plug
arrangement so you could match it. Some valve radios had a high
impedance output, so presumably both connections would be at (more
or less) HT voltage above the radio chassis (which would be earth
if the earth socket was connected). I think there were high
impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because
there are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't
require a transformer. And, of course, high impedance headphones if
you don't want a loudspeaker.
Its NOT juts a matter of impedance - its a matter of DC bias. You
cannot build a
valve amplifier that delivers true AC without an isolation
transformer. Loudspeakers don't like DC bias
That's true also for transistors, and we don't normally use
transformers. We use capacitors.
On 2026-09-29 17:54, Jan Panteltje wrote:
Max Demian <max_demian@bigfoot.com>wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way >>>>> that there were boxes you connected to the "extension speaker" socket >>>>> of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could >>>>> match it. Some valve radios had a high impedance output, so presumably >>>>> both connections would be at (more or less) HT voltage above the radio >>>>> chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Yes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm
speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
I'm not familiar with valves EZ80 and 6CA4, I don't understand the
drawings. :-?
the EL504s use the bottom one being driven to conduct more which pulls
the cathode voltage of the other down, making it a class A output stage.
On 2026-09-29 14:05, The Natural Philosopher wrote:
On 29/09/2026 12:01, Max Demian wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way that there were boxes you connected to the "extension speaker" socket of the main (valve) radio so you could listen in the kitchen. I had one which had a transformer and a wander plug arrangement so you could match it. Some valve radios had a high impedance output, so presumably both connections would be at (more or less) HT voltage above the radio chassis (which would be earth if the earth socket was connected). I think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require a transformer. And, of course, high impedance headphones if you don't want a loudspeaker.
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot build a
valve amplifier that delivers true AC without an isolation transformer. Loudspeakers don't like DC bias
That's true also for transistors, and we don't normally use transformers. We use capacitors.
Did you know he'd _specifically_ made his works - including recordings - public domain? Nice man.
On 30/09/2026 11:19, John Williamson wrote:
the EL504s use the bottom one being driven to conduct more which pulls
the cathode voltage of the other down, making it a class A output stage.
Yes, the use of the top one is something I hadn't seen before, but it certainly works.
Lot of heat for not much power, and You would get more out of e.g. a
single EL34 with a transformer.
Or a pair.
Back in the day transformers were cheap. Today they are sadly not. The
output transformer is probably at least half the component cost of a
valve amplifier...
J. P. Gilliver <G6JPG@255soft.uk> wrote:
[About Tom Lehrer:]
Did you know he'd _specifically_ made his works - including recordings -
public domain? Nice man.
Not that it matters, but according to international law (the Bern Convention), you can't actually do that (declare your work to be public domain). Whatever you do, you still have (misnomer:) copyright, or
better, author's rights. But you *can* declare your works to be freely copyable, modifyable, <whatever>, which effectively amounts to - but is
not - the same as 'public domain'. (In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction, even that doesn't 'help'.)
As an example, I have the 'copyright'/authors rights to this post, but
of course I implicitly give permission to copy it, but I do *not* lose
my author's right to be properly attributed when quoted, i.e. quoting
without attribution is not permitted (and yes, we have threathened with
legal action against a person who intentionally violated that author's
right over and over).
[...]
'totem pole' output stages using valves and, later, PNP germainum transistors with no transformers. They weren't 'kludges', they were--
good commercial designs.
Also complementary-output (differential) designs.
On 30/09/2026 11:19, John Williamson wrote:
the EL504s use the bottom one being driven to conduct more which pulls
the cathode voltage of the other down, making it a class A output stage.
Yes, the use of the top one is something I hadn't seen before, but it certainly works.
Lot of heat for not much power, and You would get more out of e.g. a
single EL34 with a transformer.
"Carlos E.R." <robin_listas@es.invalid>wrote:
On 2026-09-29 17:54, Jan Panteltje wrote:
Max Demian <max_demian@bigfoot.com>wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way >>>>> that there were boxes you connected to the "extension speaker" socket >>>>> of the main (valve) radio so you could listen in the kitchen. I had
one which had a transformer and a wander plug arrangement so you could >>>>> match it. Some valve radios had a high impedance output, so presumably >>>>> both connections would be at (more or less) HT voltage above the radio >>>>> chassis (which would be earth if the earth socket was connected). I
think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there
are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require
a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Yes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
I'm not familiar with valves EZ80 and 6CA4,
I don't understand the drawings. :-?
--
Cheers, Carlos.
ESEfc-Efc+, EUEfc-Efc|;
On Wed, 9/30/2026 5:23 AM, Carlos E.R. wrote:
On 2026-09-29 14:05, The Natural Philosopher wrote:
On 29/09/2026 12:01, Max Demian wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way that there were boxes you connected to the "extension speaker" socket of the main (valve) radio so you could listen in the kitchen. I had one which had a transformer and a wander plug arrangement so you could match it. Some valve radios had a high impedance output, so presumably both connections would be at (more or less) HT voltage above the radio chassis (which would be earth if the earth socket was connected). I think there were high impedance horn extension speakers at one time.
Valve amps ALWAYS have an output transformer. Not least because there are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require a transformer. And, of course, high impedance headphones if you don't want a loudspeaker.
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot build a
valve amplifier that delivers true AC without an isolation transformer. Loudspeakers don't like DC bias
That's true also for transistors, and we don't normally use transformers. We use capacitors.
Example of a bridged amplifier for direct drive of a speaker.
This typically puts around 3mV of DC across the speaker cone.
I have one of these on the Test Machine, driving old bookshelf speakers.
https://www.circuitbasics.com/wp-content/uploads/2016/10/TDA2003-Bridged-Amplifier-Schematic.png
The single ended version (driving speaker with respect to ground),
uses a 1000uF capacitor to block the DC.
https://www.circuitbasics.com/wp-content/uploads/2016/10/TDA2003-Stereo-Amplifier-Schematic.png
The voltage you can run that at, is +18V, as it's an automotive amplifier
and expects to be run off a car battery. And 18V is about as much as you
can expect (exclusive of load-dumps).
Paul--
In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction,
On 30/09/2026 11:57, The Natural Philosopher wrote:
On 30/09/2026 11:19, John Williamson wrote:Assuming the transformer could handle the bandwidth. The output from the circuit given would be flatter and less distorted, even across the audio bandwidth, assuming a resistive load.
the EL504s use the bottom one being driven to conduct more which pulls
the cathode voltage of the other down, making it a class A output stage.
Yes, the use of the top one is something I hadn't seen before, but it
certainly works.
Lot of heat for not much power, and You would get more out of e.g. a
single EL34 with a transformer.
As the designer saw fit to use smoothed DC for the heater of the input valve, avoiding noise and hum were obviously a priority.
On 30/09/2026 13:25, Frank Slootweg wrote:
In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction,
So no copyright on classical music anymore
On 30/09/2026 13:25, Frank Slootweg wrote:
In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction,
So no copyright on classical music anymore
On 30/09/2026 14:31, The Natural Philosopher wrote:
On 30/09/2026 13:25, Frank Slootweg wrote:
In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction,
So no copyright on classical music anymore
I've always wondered why copyright is deemed to expire some period (eg
70 years) after the *death* of the author, rather than dating from the creation/publication of the work when copyright (and now, author's
rights) is first asserted. It means that works created when the author
was young earn far more royalties and are protected for a lot longer
than those created near the end of his life.
Its NOT juts a matter of impedance - its a matter of DC bias. You cannot
build a
valve amplifier that delivers true AC without an isolation transformer.
Loudspeakers don't like DC bias
That's true also for transistors, and we don't normally use
transformers. We use capacitors.
On 30/09/2026 13:25, Frank Slootweg wrote:
In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction,
So no copyright on classical music anymore
On 30/09/2026 13:54, John Williamson wrote:
On 30/09/2026 11:57, The Natural Philosopher wrote:
On 30/09/2026 11:19, John Williamson wrote:Assuming the transformer could handle the bandwidth. The output from the circuit given would be flatter and less distorted, even across the audio bandwidth, assuming a resistive load.
the EL504s use the bottom one being driven to conduct more which pulls >>> the cathode voltage of the other down, making it a class A output stage. >>Yes, the use of the top one is something I hadn't seen before, but it
certainly works.
Lot of heat for not much power, and You would get more out of e.g. a
single EL34 with a transformer.
Not hard to do a 50-30Khz transformer .
On 30/09/2026 12:37, Paul wrote:
On Wed, 9/30/2026 5:23 AM, Carlos E.R. wrote:
Automotive-a is 13.8V rated and that/s it. The alternators wont go
higher. Which is why you use bridged amps
On 30/09/2026 10:27, Carlos E.R. wrote:
On 2026-09-29 17:54, Jan Panteltje wrote:
The EZZ80 and BCA4 valves are full wave rectifiers in the power supply. (Equivalent to two diodes in each-a valve, with a tapped transformer secondary. Back when semiconductors were expensive, I've done similarYes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm
speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/
H2qcMWJ3tuA/s1600/Schema.png
I'm not familiar with valves EZ80 and 6CA4, I don't understand the
drawings. :-?
with a pair of germanium diodes, as it was cheaper than a bridge rectifier.)i
The relevant stage for this thread is the output stage, which is two
EL504 pentodes being driven in a sort of push-pull configuration by the input triode. The EL504s each have an independent DC supply.
The circuit specifies an 800 ohm load, but I first expected to see a
more standard 600 ohm load...
"Carlos E.R." <robin_listas@es.invalid>wrote:
On 2026-09-29 17:54, Jan Panteltje wrote:
Max Demian <max_demian@bigfoot.com>wrote:
On 28/09/2026 16:46, The Natural Philosopher wrote:
On 28/09/2026 14:03, Max Demian wrote:
Yes, I suppose there could be a matching transformer, in the same way >>>>>> that there were boxes you connected to the "extension speaker" socket >>>>>> of the main (valve) radio so you could listen in the kitchen. I had >>>>>> one which had a transformer and a wander plug arrangement so you could >>>>>> match it. Some valve radios had a high impedance output, so presumably >>>>>> both connections would be at (more or less) HT voltage above the radio >>>>>> chassis (which would be earth if the earth socket was connected). I >>>>>> think there were high impedance horn extension speakers at one time. >>>>Valve amps ALWAYS have an output transformer. Not least because there >>>>> are no 'P channel ' valves.
I think there were high impedance horn speakers, which wouldn't require >>>> a transformer. And, of course, high impedance headphones if you don't
want a loudspeaker.
Yes some tube TVs had 800 Ohm speakers without transformers.
Example of a tube output stage without transformer to drive a 800 Ohm speaker:
https://2.bp.blogspot.com/-GaJkZ9klfLw/VOecHjVgPuI/AAAAAAAAA4g/H2qcMWJ3tuA/s1600/Schema.png
I'm not familiar with valves EZ80 and 6CA4,
https://www.radiomuseum.org/tubes/tube_ez80.html
Both those tube you mention have 2 anodes and one cathode,
each are used as 2 diodes to make 347 V from two opposite phase transformer outputs, to give a power line with less ripple (100 Hz versus a 50 Hz ripple or 120 Hz versus 60 Hz in 'merryca, as in case of one diode,
that way needing less supply filtering, allows smaller filter capacitors to be
used,
anode1
0----->|----
|--0 -cathode
0----->|----
anode2
I don't understand the drawings. :-?
It is a schematic diagram shows how the 'tubes' are connected.
You need some electronics expericne to understand thsoe circuit.
On 2026-09-30 15:28, The Natural Philosopher wrote:
On 30/09/2026 12:37, Paul wrote:
On Wed, 9/30/2026 5:23 AM, Carlos E.R. wrote:
Automotive-a is 13.8V rated and that/s it. The alternators wont go
higher. Which is why you use bridged amps
I have seen 15 volts.
Any mains powered amplifier hums a bit. And even ones that are not.
mains hum fields are all pervasive
The best one I have has an SMPS power supply feeding a class D
amplifier. Feels way too light for the power
On 30/09/2026 14:47, NY wrote:No (for long-dead composers, anyway - there are composers well into the
On 30/09/2026 14:31, The Natural Philosopher wrote:
On 30/09/2026 13:25, Frank Slootweg wrote:
In some juridictions you have to be
dead for 70 years or so, for your work to become public domain and in
other juridiction,
So no copyright on classical music anymore
I've always wondered why copyright is deemed to expire some period (eg
70 years) after the *death* of the author, rather than dating from the
creation/publication of the work when copyright (and now, author's
rights) is first asserted. It means that works created when the author
was young earn far more royalties and are protected for a lot longer
than those created near the end of his life.
The official reason is to provide an income for any surviving family members.
On 2026/9/30 23:35:42, Carlos E. R. wrote:
On 2026-09-30 15:28, The Natural Philosopher wrote:The source (of the power) may not go very high, but all sorts of
On 30/09/2026 12:37, Paul wrote:
On Wed, 9/30/2026 5:23 AM, Carlos E.R. wrote:
Automotive-a is 13.8V rated and that/s it. The alternators wont go
higher. Which is why you use bridged amps
I have seen 15 volts.
transients get onto an automotive supply - I think it would be unwise
not to design such equipment to _withstand_ 50-100 volts on the supply
line, even if it only expects to _work_ on say 12-15. (fairly simple protection - chokes and capacitors, possibly followed by beefy zeners - should be sufficient.)
"Carlos E. R." <robin_listas@es.invalid>wrote:
I'm not familiar with valves EZ80 and 6CA4,
https://www.radiomuseum.org/tubes/tube_ez80.html
Both those tube you mention have 2 anodes and one cathode,
each are used as 2 diodes to make 347 V from two opposite phase transformer >> outputs, to give a power line with less ripple (100 Hz versus a 50 Hz ripple >> or 120 Hz versus 60 Hz in 'merryca, as in case of one diode,
that way needing less supply filtering, allows smaller filter capacitors to be
used,
anode1
0----->|----
|--0 -cathode
0----->|----
anode2
I don't understand the drawings. :-?
It is a schematic diagram shows how the 'tubes' are connected.
You need some electronics expericne to understand thsoe circuit.
I am an electronics engineer :-)
What I don't understand is why the two anodes have different sizes.
"J. P. Gilliver" <G6JPG@255soft.uk>wrote:
On 2026/9/30 14:34:42, The Natural Philosopher wrote:[]
Any mains powered amplifier hums a bit. And even ones that are not.Yes, I have one of those - came with an external supply, similar to
mains hum fields are all pervasive
The best one I have has an SMPS power supply feeding a class D
amplifier. Feels way too light for the power
(probably identical to) the sort that comes with laptops (or did a few
years ago: modern laptop ones are tiny). Yes, far too small and light
for the power - because with modern transistors, class D dissipates
hardly any (waste, heating) power in the output transistors, so needs
hardly any heatsinking, which is much of the weight in a transistor >amplifier. I think mine is rated something like 50W (might be per
channel!), and is about fag-packet size - really just big enough to
support the connectors and volume knob.
"Carlos E. R." <robin_listas@es.invalid>wrote:
I'm not familiar with valves EZ80 and 6CA4,
https://www.radiomuseum.org/tubes/tube_ez80.html
Both those tube you mention have 2 anodes and one cathode,
each are used as 2 diodes to make 347 V from two opposite phase transformer >>> outputs, to give a power line with less ripple (100 Hz versus a 50 Hz ripple
or 120 Hz versus 60 Hz in 'merryca, as in case of one diode,
that way needing less supply filtering, allows smaller filter capacitors to be
used,
anode1
0----->|----
|--0 -cathode
0----->|----
anode2
I don't understand the drawings. :-?
It is a schematic diagram shows how the 'tubes' are connected.
You need some electronics expericne to understand thsoe circuit.
I am an electronics engineer :-)
Practical experience with tubes?
What I don't understand is why the two anodes have different sizes.
In the drawing?
Maybe just a drawing error / constraint.
https://www.radiomuseum.org/tubes/tube_ez80.html
Both anodes look the same size to me!
IIRC I have used that tube in the long ago past.
"Carlos E. R." <robin_listas@es.invalid>wrote:
I'm not familiar with valves EZ80 and 6CA4,
https://www.radiomuseum.org/tubes/tube_ez80.html
Both those tube you mention have 2 anodes and one cathode,
each are used as 2 diodes to make 347 V from two opposite phase transformer >>> outputs, to give a power line with less ripple (100 Hz versus a 50 Hz ripple
or 120 Hz versus 60 Hz in 'merryca, as in case of one diode,
that way needing less supply filtering, allows smaller filter capacitors to be
used,
anode1
0----->|----
|--0 -cathode
0----->|----
anode2
I don't understand the drawings. :-?
It is a schematic diagram shows how the 'tubes' are connected.
You need some electronics expericne to understand thsoe circuit.
I am an electronics engineer :-)
Practical experience with tubes?
What I don't understand is why the two anodes have different sizes.
In the drawing?
Maybe just a drawing error / constraint.
https://www.radiomuseum.org/tubes/tube_ez80.html
Both anodes look the same size to me!
IIRC I have used that tube in the long ago past.
On 30/09/2026 13:54, John Williamson wrote:[...]
As the designer saw fit to use smoothed DC for the heater of the input valve, avoiding noise and hum were obviously a priority.
Any mains powered amplifier hums a bit. And even ones that are not.
mains hum fields are all pervasive
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