From Newsgroup: sci.electronics.repair

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to
maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

CD.
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From Newsgroup: sci.electronics.repair

Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

I'd think you want clean and dry surfaces. Any lubricant is going to
be an insulator, as is (most) dust it traps. A little more contact
pressure seems a liklier bet without actually seeing and handling
the device.

Is it possible to verfy the poor contact hypothesis with an ohmmeter?

It's possible to make conductive pastes by adding metal or carbon powder
to to a viscous fluid, but the conductivity is poor comparatively.

bob prohaska

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From Newsgroup: sci.electronics.repair

In article <21u9ekdg7tl0u7jgtiicc7563l70pagmlr@4ax.com>,
Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to >maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

Check out "NO-OX-ID A-Special" antioxidant grease - it's made
specifically for this sort of purpose.

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From Newsgroup: sci.electronics.repair

On Tue, 7 Oct 2025 12:13:37 -0700, dplatt@coop.radagast.org (Dave
Platt) wrote:

In article <21u9ekdg7tl0u7jgtiicc7563l70pagmlr@4ax.com>,
Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to >>maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

Check out "NO-OX-ID A-Special" antioxidant grease - it's made
specifically for this sort of purpose.

Thanks, Dave. I'll give it a shot.
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From Newsgroup: sci.electronics.repair

Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

CD.

Powdered graphite used for locks perhaps?
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From Newsgroup: sci.electronics.repair

On Sun, 12 Oct 2025 18:38:50 -0000 (UTC), Jerry Peters
<jerry@example.invalid> wrote:

Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to
maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

CD.

Powdered graphite used for locks perhaps?

Powder? Not so much. But they do make a graphite grease and I plan to
try that if the other ideas fail.
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From Newsgroup: sci.electronics.repair

On 12/10/2025 23:13, Cursitor Doom wrote:

On Sun, 12 Oct 2025 18:38:50 -0000 (UTC), Jerry Peters <jerry@example.invalid> wrote:

Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to
maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

CD.

Powdered graphite used for locks perhaps?

Powder? Not so much. But they do make a graphite grease and I plan to
try that if the other ideas fail.

Limiting the spread of a very fine conductive powder might be easier
said than done!

Apart from graphite grease, have you considered a molybdenum sulfide
based grease? It's also conductive, and MoS2 has similar properties to graphite as a lubricant. However, according to <https://greaseco.com/blogs/grease-articles/what-is-moly-grease-best-used-for>,
"Conductivity issues can arise from the use of moly grease in electrical connections."
--
Jeff
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From Newsgroup: sci.electronics.repair

Cursitor Doom <cd@notformail.com> wrote:

On Sun, 12 Oct 2025 18:38:50 -0000 (UTC), Jerry Peters <jerry@example.invalid> wrote:

Cursitor Doom <cd@notformail.com> wrote:

Hi all,

I've got this old Grundig radio made in 1972 and the main tuning cap
gets scratchy from time to time owing to a design defect where they've
put the moving contact at 90 degrees to the shaft so it runs in a
narrow slot, rather than the more common leaf spring contact. Over
time, this has worn and as it has, it doesn't self-correct for tension
like the leaf type does. So I've been using a switch cleaning
lubricant on it, which works great for about 6 weeks, but then it's
getting scratchy again. Is there something more permanent I can use to
maintain good contact? I'm thinking maybe copper grease like the stuff
they use on brake pads to stop squealing. Would that work? Switch
lubricant fluid is just not sludgy enough to stick around!

CD.

Powdered graphite used for locks perhaps?

Powder? Not so much. But they do make a graphite grease and I plan to
try that if the other ideas fail.

With conductive particles in a non-conductive medium, the proportion of conductive material is quite critical. Conduction only begins to occur
when there are enough particles to touch each other, so you will need to
check your graphite grese for conductivity with a couple of ohm-meter
prods. You might be better off adding just enough grease to graphite
powder to make it stick and not blow about.

(This explains why most zinc-based primers are useless, because the zinc particles aren't touching and cannot contribute any electrolytic
action.)
--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk
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