'63 Tremolux with scratchy pots

[SteveInMN]

I have a '63 Tremolux that runs great, except for scratchy pots, the Treble pot on the Normal channel and the Volume and Treble on the Bright channel.
I understand this is more often a cap problem than a pot problem.
But there are a lot of caps, and most are the molded blues that one doesn't want to toss without educated reasons. Of which I have none.
Any advice on where to start?
Is it a matter of testing for DC voltage on each cap while the amp is powered up, and replacing the worst ones?
I have no diagnostic equipment beyond a standard multimeter. 
Schematic attached, noisy pots circled. 

[Latole]

Scratchy pots

1- They may need to be clean with good contact cleaner ; most of the time, it is the issue.
     Spray contact in pots access holes and turn shaft 0 t 10 at least 20 times
     More you use / turn pot shaft in real life, less issue you will have on a amps or guitars pots. 

2- Or it is a leaky cap feeding these pots

3- Or it is 1 and 2

Check DC volt on all caps connected to these pots ; on side of the cap you will have DC volts, other side nothing.
You should not read any volts on pots

.0005, .1 , .05

[pdf64]

That black vulcanised card circuit board can cause this, make good caps appear bad.

[Latole]

That black vulcanised card circuit board can cause this, make good caps appear bad.

Oh !
How can he fix it ?

IMO, disconnecting the cap from the pot side , we should read no voltage ,black vulcanized card board or not . Right ?
 

[punkykatt]

The eyelet board may have become conductive. I have had several amps in my shop with that. Not a fun job replacing the eyelet board.

[Latole]

The eyelet board may have become conductive. I have had several amps in my shop with that. Not a fun job replacing the eyelet board.

Not fun and very expensive for your customer.

[SteveInMN]

Scratchy pots

1- They may need to be clean with good contact cleaner ; most of the time, it is the issue.
     Spray contact in pots access holes and turn shaft 0 t 10 at least 20 times
     More you use / turn pot shaft in real life, less issue you will have on a amps or guitars pots. 

2- Or it is a leaky cap feeding these pots

3- Or it is 1 and 2

Check DC volt on all caps connected to these pots ; on side of the cap you will have DC volts, other side nothing.
You should not read any volts on pots

.0005, .1 , .05

I should have mentioned that I have hit the worst of the pots (V on Bright) a couple times w/ DeOxit; problem goes away for  while, but it comes back.

I will test those caps; basically - put the negative MM lead to ground, test for DC at both ends of each cap, is that right? Is there 'any' level of leakage that is acceptable, or are we talking binary here?

Thanks!

[SteveInMN]

That black vulcanised card circuit board can cause this, make good caps appear bad.

Yes, that's a possibility. How do I test for that? Just put the probes to different spots on the board and look for any DC (which s/b "0", right?)

[punkykatt]

Yes.

[Willabe]

I will test those caps; basically - put the negative MM lead to ground, test for DC at both ends of each cap, is that right? Is there 'any' level of leakage that is acceptable, or are we talking binary here?

No.

You lift/unsolder the caps lead that is not connected to the tube plate. Tube plate has dcv on it.

Lift that end of the cap up in the air. Use alligator clips on your leads. Set meter for dcv. Clip 1 meter lead to the still soldered in place cap lead and the other to the cap lead that's up in the air. Now turn on the amp, take reading.

Don't forget to dis charge the cap, it will have dcv on it now.

Should be less than 1dcv, the lower the better.

[Latole]

That black vulcanised card circuit board can cause this, make good caps appear bad.

Yes, that's a possibility. How do I test for that? Just put the probes to different spots on the board and look for any DC (which s/b "0", right?)

Yes

 Can we say ;

1- If you disconnect the caps on pot side ; you won't read any volts even if cardboard is conductive.
    You can conclude caps is good.
2- If the pot is new ( or clean like new ) and it is scratchy ; issue is not the pot

3- If we read volts on cardboard. Issue is the board
 
 

[Latole]

Scratchy pots

1- They may need to be clean with good contact cleaner ; most of the time, it is the issue.
     Spray contact in pots access holes and turn shaft 0 t 10 at least 20 times
     More you use / turn pot shaft in real life, less issue you will have on a amps or guitars pots. 

2- Or it is a leaky cap feeding these pots

3- Or it is 1 and 2

Check DC volt on all caps connected to these pots ; on side of the cap you will have DC volts, other side nothing.
You should not read any volts on pots

.0005, .1 , .05

1- I should have mentioned that I have hit the worst of the pots (V on Bright) a couple times w/ DeOxit; problem goes away for  while,         but it comes back.

2-I will test those caps; basically - put the negative MM lead to ground, test for DC at both ends of each cap, is that right? Is there 'any' level of leakage that is acceptable, or are we talking binary here?

Thanks!

1- Pots is bad, put new one. It is happened to me
2- Voltage in one side = 0 volts on the other side . Any 1/10  volts is unacceptable

[Latole]

That black vulcanised card circuit board can cause this, make good caps appear bad.

Yes, that's a possibility. How do I test for that? Just put the probes to different spots on the board and look for any DC (which s/b "0", right?)

Did you try a wire screw to the board and to the amp ground. ?     I should drop voltage to 0

[SteveInMN]

Thanks for the thoughts, folks, all good, now I have a plan!