From Newsgroup: sci.electronics.design

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before
full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
| | |
[R1] +--o o----+ ___________
| \ | | Xformer |
[D1] +-[rly]-+ +---|P S|---
| | | |R E|
+---+-[C1]--+--+---|I C|---
| |_________|
|
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor.
R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

Ed
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 10/10/2025 1:09 PM, ehsjr wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes surges.-a It allows the tubes to "warm up" for some period of time before full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
-a-a-a-a-a |-a-a |-a-a-a-a-a-a-a-a-a |
-a-a-a-a [R1] +--o-a o----+-a-a ___________
-a-a-a-a-a |-a-a-a-a-a-a \-a-a-a-a-a |-a-a | Xformer |
-a-a-a-a [D1] +-[rly]-+-a +---|P-a-a-a-a-a-a S|---
-a-a-a-a-a |-a-a |-a-a-a-a-a-a |-a-a-a-a-a |R-a-a-a-a-a-a E|
-a-a-a-a-a +---+-[C1]--+--+---|I-a-a-a-a-a-a C|---
-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a |-a-a |_________|
-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a |
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor.
R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

I used a similar approach in some hifi amplifiers I designed in
the 70's -- but, put the series resistance in the secondaries
to reduce the surge into the bulk filter caps. It also
allowed me to use them to discharge the caps when power was
removed (instead of having +-80VDC sitting there for a small
eternity and the risk of exposure when you decoupled the
supply from the amp).

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 10/10/2025 8:09 PM, Don Y wrote:

On 10/10/2025 1:09 PM, ehsjr wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges.-a It allows the tubes to "warm up" for some period of time before
full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
-a-a-a-a-a-a |-a-a |-a-a-a-a-a-a-a-a-a |
-a-a-a-a-a [R1] +--o-a o----+-a-a ___________
-a-a-a-a-a-a |-a-a-a-a-a-a \-a-a-a-a-a |-a-a | Xformer |
-a-a-a-a-a [D1] +-[rly]-+-a +---|P-a-a-a-a-a-a S|---
-a-a-a-a-a-a |-a-a |-a-a-a-a-a-a |-a-a-a-a-a |R-a-a-a-a-a-a E|
-a-a-a-a-a-a +---+-[C1]--+--+---|I-a-a-a-a-a-a C|---
-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a |-a-a |_________|
-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a |
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor.
R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

I used a similar approach in some hifi amplifiers I designed in
the 70's -- but, put the series resistance in the secondaries
to reduce the surge into the bulk filter caps.-a It also
allowed me to use them to discharge the caps when power was
removed (instead of having +-80VDC sitting there for a small
eternity and the risk of exposure when you decoupled the
supply from the amp).

A nice advantage of your approach is that you can save 2 parts
(D1 and C1) in some cases if you want. Just use B+ from the
device itself. AND it will work fine if the transformer includes
the filament winding, without delaying the tubes heating up.

I didn't want to recommend that in the original post, as
anyone could read it and attempt to do wiring on higher
voltages areas (where higher in this case means above mains
voltage - perhaps up to 4000 volts in some linear amplifiers).
Many are qualified to do that of course, but far more are not.

Ed
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 10/11/2025 7:43 PM, ehsjr wrote:

On 10/10/2025 8:09 PM, Don Y wrote:

On 10/10/2025 1:09 PM, ehsjr wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges.-a It allows the tubes to "warm up" for some period of time before >>> full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
-a-a-a-a-a-a |-a-a |-a-a-a-a-a-a-a-a-a |
-a-a-a-a-a [R1] +--o-a o----+-a-a ___________
-a-a-a-a-a-a |-a-a-a-a-a-a \-a-a-a-a-a |-a-a | Xformer |
-a-a-a-a-a [D1] +-[rly]-+-a +---|P-a-a-a-a-a-a S|---
-a-a-a-a-a-a |-a-a |-a-a-a-a-a-a |-a-a-a-a-a |R-a-a-a-a-a-a E|
-a-a-a-a-a-a +---+-[C1]--+--+---|I-a-a-a-a-a-a C|---
-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a |-a-a |_________|
-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a |
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor. >>> R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

I used a similar approach in some hifi amplifiers I designed in
the 70's -- but, put the series resistance in the secondaries
to reduce the surge into the bulk filter caps.-a It also
allowed me to use them to discharge the caps when power was
removed (instead of having +-80VDC sitting there for a small
eternity and the risk of exposure when you decoupled the
supply from the amp).

A nice advantage of your approach is that you can save 2 parts
(D1 and C1) in some cases if you want. Just use B+ from the
device itself. AND it will work fine if the transformer includes
the filament winding, without delaying the tubes heating up.

My amps were solid state so a lower B+/B-.

I had a small 12V power supply to power some discretes that
would sequence the power supply, control indicators, etc.
E.g., press this LPB to power up and this to power down;
configure to cascade to the next power supply; etc.

I was triamping so having all those power supplies trying
to charge their filter caps was brutal on a dorm room's
power availability. <frown>

I didn't want to recommend that in the original post, as
anyone could read it and attempt to do wiring on higher
voltages areas (where higher in this case means above mains
voltage - perhaps up to 4000 volts in some linear amplifiers).
Many are qualified to do that of course, but far more are not.

I was mainly concerned that someone (likely me!) would
unplug the amplifiers from their power supplies and there
would be no loads to ensure the caps got discharged.

Then, replug the amps and worry which conductors make
contact in which order (with +-B on those pins), etc.

It was easier to just shrink the "window of vulnerability"
to something that made that less likely to occur AND speed
things up in the process.

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before
full high voltage is applied.

In particular, higher powered equipment with mercury rectifiers needed
the heaters on for some time before the HT could be applied. This was
to evaporate mercury that had collected in the wrong place with the risk
of a flashover.

With equipment like that it was quite normal to have a separate HT
transformer, so a relay could switch the primary. The relay was
controlled by a delay system which used a special delay switch that
consisted of a heater and a bimetal strip inside an evacuated envelope.
It plugged into a B9A base and looked exactly like a normal valve.

In equipment with a separate lower-voltage HT supply, a spare valve
(such as the unused half of an ECC82) could be used with the grid
strapped to the cathode and the relay coil in the anode circuit. The
relay could not operate until the valve had warmed up and started
passing anode current.
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Fri, 10 Oct 2025 16:09:47 -0400, ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before
full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
| | |
[R1] +--o o----+ ___________
| \ | | Xformer |
[D1] +-[rly]-+ +---|P S|---
| | | |R E|
+---+-[C1]--+--+---|I C|---
| |_________|
|
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor.
R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

Ed

(Leaving aside the fact that this has already been satisfactorily
resolved)
I don't wish to cast nasturtiums on your design abilities, but you
can't come up with a valid design for anything until you know the full
circs of what you're designing for. In the case of the two PSUs in
question, they're not giving an initial surge in the
commonly-understood sense. I'll explain for the purposes of
illustration, step-by-step, what happens.

1. Initial power-up/switch on. Indicated voltage immedilately climbs
to about 1/3 of indicated Vout.
2. Hiatus of around 10 seconds.
3. Vout begins to climb at an exponential rate, surging to up to 50%
above indicated Vout, then falls back to a point where the true Vout
and indicated Vout match each other.

The above holds for both my HT PSUs. The low voltage PSU I'm using
*does* however surge at switch-on in the conventional way, stressing
the heaters of the tubes I'm testing. So that could be dealt with by
your methodology. Or I could just swap over to a PSU that doesn't do
that. :)
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Sun, 12 Oct 2025 10:52:21 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before
full high voltage is applied.

In particular, higher powered equipment with mercury rectifiers needed
the heaters on for some time before the HT could be applied. This was
to evaporate mercury that had collected in the wrong place with the risk
of a flashover.

Early utility DC links used ignitrons.

https://en.wikipedia.org/wiki/Ignitron

With equipment like that it was quite normal to have a separate HT >transformer, so a relay could switch the primary. The relay was
controlled by a delay system which used a special delay switch that
consisted of a heater and a bimetal strip inside an evacuated envelope.
It plugged into a B9A base and looked exactly like a normal valve.

The big old Tek tube scopes usually had that arrangement.

In equipment with a separate lower-voltage HT supply, a spare valve
(such as the unused half of an ECC82) could be used with the grid
strapped to the cathode and the relay coil in the anode circuit. The
relay could not operate until the valve had warmed up and started
passing anode current.

John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Sun, 12 Oct 2025 11:42:26 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Fri, 10 Oct 2025 16:09:47 -0400, ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes >>surges. It allows the tubes to "warm up" for some period of time before >>full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
| | |
[R1] +--o o----+ ___________
| \ | | Xformer |
[D1] +-[rly]-+ +---|P S|---
| | | |R E|
+---+-[C1]--+--+---|I C|---
| |_________|
|
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor.
R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

Ed

(Leaving aside the fact that this has already been satisfactorily
resolved)
I don't wish to cast nasturtiums on your design abilities, but you
can't come up with a valid design for anything until you know the full
circs of what you're designing for. In the case of the two PSUs in
question, they're not giving an initial surge in the
commonly-understood sense. I'll explain for the purposes of
illustration, step-by-step, what happens.

1. Initial power-up/switch on. Indicated voltage immedilately climbs
to about 1/3 of indicated Vout.
2. Hiatus of around 10 seconds.
3. Vout begins to climb at an exponential rate, surging to up to 50%
above indicated Vout, then falls back to a point where the true Vout
and indicated Vout match each other.

The above holds for both my HT PSUs. The low voltage PSU I'm using
*does* however surge at switch-on in the conventional way, stressing
the heaters of the tubes I'm testing. So that could be dealt with by
your methodology. Or I could just swap over to a PSU that doesn't do
that. :)

You could make an external box, with two dual banana jacks, that opens
the path until you push a button. That could be a fun design.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On 10/12/2025 6:42 AM, Cursitor Doom wrote:

On Fri, 10 Oct 2025 16:09:47 -0400, ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before
full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
| | |
[R1] +--o o----+ ___________
| \ | | Xformer |
[D1] +-[rly]-+ +---|P S|---
| | | |R E|
+---+-[C1]--+--+---|I C|---
| |_________|
|
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor.
R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

Ed

(Leaving aside the fact that this has already been satisfactorily
resolved)
I don't wish to cast nasturtiums on your design abilities, but you
can't come up with a valid design for anything until you know the full
circs of what you're designing for. In the case of the two PSUs in
question, they're not giving an initial surge in the
commonly-understood sense. I'll explain for the purposes of
illustration, step-by-step, what happens.

1. Initial power-up/switch on. Indicated voltage immedilately climbs
to about 1/3 of indicated Vout.
2. Hiatus of around 10 seconds.
3. Vout begins to climb at an exponential rate, surging to up to 50%
above indicated Vout, then falls back to a point where the true Vout
and indicated Vout match each other.

The typical circuit handles that, in general. The assumption
in the typical circuit is that there needs to be a delay in
order for the tubes to warm up before full B+ is applied.
As you said, I don't know the specifics of your particular
equipment, thus I posted a typical design, not something
designed for your specific problem. It has nothing to do
with my design abilities - but I do like nasturtiums! :-)

Anyway, it's not my design, it's in the published literature
concerning soft start circuits. You might enjoy reading https://www.meanwelldirect.co.uk/glossary/what-does-soft-start-mean/
or other references you can Google.

Back to the circuit. As I mentioned, you can use it to
switch the output on after delay time, which seems to be
what you have decided after asking Liz about that (?)
You can decide how to use it - or whether to use it -
based on your specific equipment. It's simple and
automatic.

Ed

The above holds for both my HT PSUs. The low voltage PSU I'm using
*does* however surge at switch-on in the conventional way, stressing
the heaters of the tubes I'm testing. So that could be dealt with by
your methodology. Or I could just swap over to a PSU that doesn't do
that. :)

--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

On Sun, 12 Oct 2025 13:15:40 -0400, ehsjr <ehsjr@verizon.net> wrote:

On 10/12/2025 6:42 AM, Cursitor Doom wrote:

On Fri, 10 Oct 2025 16:09:47 -0400, ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before >>> full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
| | |
[R1] +--o o----+ ___________
| \ | | Xformer |
[D1] +-[rly]-+ +---|P S|---
| | | |R E|
+---+-[C1]--+--+---|I C|---
| |_________|
|
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor. >>> R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

Ed

(Leaving aside the fact that this has already been satisfactorily
resolved)
I don't wish to cast nasturtiums on your design abilities, but you
can't come up with a valid design for anything until you know the full
circs of what you're designing for. In the case of the two PSUs in
question, they're not giving an initial surge in the
commonly-understood sense. I'll explain for the purposes of
illustration, step-by-step, what happens.

1. Initial power-up/switch on. Indicated voltage immedilately climbs
to about 1/3 of indicated Vout.
2. Hiatus of around 10 seconds.
3. Vout begins to climb at an exponential rate, surging to up to 50%
above indicated Vout, then falls back to a point where the true Vout
and indicated Vout match each other.

The typical circuit handles that, in general. The assumption
in the typical circuit is that there needs to be a delay in
order for the tubes to warm up before full B+ is applied.
As you said, I don't know the specifics of your particular
equipment, thus I posted a typical design, not something
designed for your specific problem. It has nothing to do
with my design abilities - but I do like nasturtiums! :-)

Anyway, it's not my design, it's in the published literature
concerning soft start circuits. You might enjoy reading >https://www.meanwelldirect.co.uk/glossary/what-does-soft-start-mean/
or other references you can Google.

Back to the circuit. As I mentioned, you can use it to
switch the output on after delay time, which seems to be
what you have decided after asking Liz about that (?)
You can decide how to use it - or whether to use it -
based on your specific equipment. It's simple and
automatic.

Yes, well doing nothing is not an option because flicking the HT on
and off is all very well - until I absent-mindedly leave it in the
'on' position (which is bound to happen sooner or later). In the mean
time, I'm hoping a pal of mine will succeed in finding a 450V
transformer in his ham stash. That way I'll avoid even having to build
anything at all. :)
--- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: sci.electronics.design

ehsjr <ehsjr@verizon.net> wrote:

On 10/12/2025 6:42 AM, Cursitor Doom wrote:

On Fri, 10 Oct 2025 16:09:47 -0400, ehsjr <ehsjr@verizon.net> wrote:

For Cursitor Doom

A typical slow start circuit for tube equipment prevents or minimizes
surges. It allows the tubes to "warm up" for some period of time before >> full high voltage is applied.

You can use the circuit below as shown, or omit R2 and use the
relay to switch the output on after the delay time

Add everything to the left of the transformer (R1, R2, D1, Rly and C1)
to your supplies after the AC input fuse.

AC----+---+--[R2]----+
| | |
[R1] +--o o----+ ___________
| \ | | Xformer |
[D1] +-[rly]-+ +---|P S|---
| | | |R E|
+---+-[C1]--+--+---|I C|---
| |_________|
|
AC-------------------+

R2 is a low resistance, say 5 ohms or less, high wattage power resistor. >> R1 drops the voltage for the relay, and with C1, sets the delay time

When C1 charges high enough, the relay transfers, shorting the
path around R2 so the transformer gets full input voltage.

Ed

(Leaving aside the fact that this has already been satisfactorily
resolved)
I don't wish to cast nasturtiums on your design abilities, but you
can't come up with a valid design for anything until you know the full circs of what you're designing for. In the case of the two PSUs in question, they're not giving an initial surge in the
commonly-understood sense. I'll explain for the purposes of
illustration, step-by-step, what happens.

1. Initial power-up/switch on. Indicated voltage immedilately climbs
to about 1/3 of indicated Vout.
2. Hiatus of around 10 seconds.
3. Vout begins to climb at an exponential rate, surging to up to 50%
above indicated Vout, then falls back to a point where the true Vout
and indicated Vout match each other.

The typical circuit handles that, in general. The assumption
in the typical circuit is that there needs to be a delay in
order for the tubes to warm up before full B+ is applied.
As you said, I don't know the specifics of your particular
equipment, thus I posted a typical design, not something
designed for your specific problem. It has nothing to do
with my design abilities - but I do like nasturtiums! :-)

Anyway, it's not my design, it's in the published literature
concerning soft start circuits. You might enjoy reading https://www.meanwelldirect.co.uk/glossary/what-does-soft-start-mean/
or other references you can Google.

Back to the circuit. As I mentioned, you can use it to
switch the output on after delay time, which seems to be
what you have decided after asking Liz about that (?)
You can decide how to use it - or whether to use it -
based on your specific equipment. It's simple and
automatic.

You don't waste the delay time, you use it to check that you really have
wired up the circuit correctly and that there are no stray wires
touching the HT and waiting to bite you. By the time you have done
that, the valves in the PSU have warmed up, the valves in your own
circuit have warmed up (no point in applying HT before they are up to temperature) and there is no further delay.
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
--- Synchronet 3.21a-Linux NewsLink 1.2