Ao44 pee wee build/vol won't shut off

[lexluthier72]

I recently finished an ao44 pee wee build. Im having signal bleed and my volume pot does not shut off all the way. Things I have done: checked all my grounds, checked my filter cap hot and ground connections, replaced the volume pot, added a filter to my 100k resistors at the preamp node. (22uf@500v) Removed extra filter, swapped tubes out. (12ax7 only) The only improvement was a short plate sovtek 12ax7. This made it quieter, but still not shut off. Hopefully Steve will chime in.

[Latole]

You can't show us schematic as built ?

I can't see nothing with your small picture.

Did  you put one side of the volume pot to ground ?

What is the value of you volume pot  ?
 

[lexluthier72]

I used the Sluckey schematic that is posted on his page. Yes, volume pot is grounded. Volume pot is 1 Meg audio

[lexluthier72]

Schematic here:
https://sluckeyamps.com/PeeWee/PeeWee.pdf

[lexluthier72]

Schematic...

[sluckey]

I recently finished an ao44 pee wee build. Im having signal bleed and my volume pot does not shut off all the way.

I see you used the original 60 year old cap can? Dried out electrolytics are a prime suspect for signal bleed. The signal bleed is probably the cause of not being able to turn the volume off too. Try putting a gator clip lead between chassis and the VOL ground lug to see if that helps, but I suspect you will need to replace the filter caps.

I was lucky and able to reform my can caps, but I was prepared to replace the can. I even bought a JJ 40/20/20/20 can to use as a replacement but didn't need it. Sounds like you may not be so lucky.

Couple things I noticed on your amp... The 1K resistor that connects from the rectifier socket to the cap can looks like it has been hot enough to discolor the color bands. I would replace it. Also, that green .1µF tonestack cap looks to be under-rated voltage wise. There is B+ voltage on that cap. I suggest using at least a 400V rating. Oh, and it needs to connect to the middle lug of the bass pot (or put a jumper between the middle lug and the right lug (as viewed in your pic.) I also see you did not use any NFB?

@Latole... His pic is plenty big enough. Schematic is here... http://sluckeyamps.com/PeeWee/peewee.htm
 

[lexluthier72]

Thank you! I will revisit the filter can. And clean up other components.

[lexluthier72]

Ive tried every suggestion. Rather than pull the can cap, I tacked in extra 22uf@500v at each node on the can. It did not fix it. Im stumped. Can my front panel layout be the issue? (Not stock like yours)

[lexluthier72]

Here's where Im at. I tacked in a 47uf@450v to the preamp node. It helped but not completely.

[dude]

Replace the can, Antique Electronics has a JJ 40,20,20,20 can for $15.95
https://www.tubesandmore.com/sites/default/files/uc_products/c-ec40-20x3-500.png

[lexluthier72]

FIXED!!!!   The fix was a brand new JJ ecc83s and a tube shield on it.

[Latole]

FIXED!!!!   The fix was a brand new JJ ecc83s and a tube shield on it.

It can't be a tube and a tube shield. It doesn't make sense

[lexluthier72]

All I can tell you is, it no longer bleeds signal. Whatever it was, it is fixed. The last thing I did was swap in a brand new tube and add a shield. Thanks for the input.

[Latole]

Sure you do something else when working in the amp .

Issue will come back

[lexluthier72]

Well, then I will have to revisit the problem then wont I? Maybe it was the 47uf cap I added.

[lexluthier72]

SO, Latole....whats next then? I added the 47uf filter to the preamp node. It helped, but then it was not all the way off. What next?

[sluckey]

You could satisfy all the naysayers simply by putting the "bad" tube back in. If problem returns you will convince the naysayers. If not, you'll understand why they are non believers.   

[lexluthier72]

Thank you STEVE! I did in fact swap tubes in and out and the original tube I used was BAD!!!! It appears to be working great!

[lexluthier72]

THIS!!!!!

You could satisfy all the naysayers simply by putting the "bad" tube back in. If problem returns you will convince the naysayers. If not, you'll understand why they are non believers.   

[sluckey]

Hear, hear, all naysayers!   

[sluckey]

BTW, you're running the amp with no NFB. Did you try NFB? How does the amp sound to you? Mine was surprisingly louder than I had expected. However, my PeeWee became a donor for a Magnatone M2. The power amp was almost identical.

[lexluthier72]

WHY NOT? Explain....?

FIXED!!!!   The fix was a brand new JJ ecc83s and a tube shield on it.

It can't be a tube and a tube shield. It doesn't make sense

[lexluthier72]

It sounds good. Plenty loud. I tried it with and without NFB. Liked it better without. Made no difference in signal bleed.

BTW, you're running the amp with no NFB. Did you try NFB? How does the amp sound to you? Mine was surprisingly louder than I had expected. However, my PeeWee became a donor for a Magnatone M2. The power amp was almost identical.

[Latole]

How a bad tube make "my volume pot does not shut off all the way. ? 

[lexluthier72]

Latole, how are any of your responses helpful? A bad/microphonic tube can in fact cause crosstalk/signal bleed. Now, Im assuming you are capable of actually explaining how its not possible. IF not, please refrain from adding more unnecessary comments that are not helpful.

[Latole]

A good answer ! I learn here.

[astronomicum]

Your original post indicated you replaced the 12AX7. Your fix ended up being a new 12AX7 (ECC83s) and a tube shield. I would be interested to know if the fix was the ECC83s, the tube shield, or the combination. Does the ECC83s fix the problem without the tube shield? If it does not, does the tube shield fix the problem on any of the other tubes you tried?

[pdf64]

How a bad tube make "my volume pot does not shut off all the way. ? 

I have no idea what the mechanism is that cause the problem, but I can attest that there’s a unusual 12AX7 failure mode which results in signal applied to one of its triode sections also appearing in the other section. As if by magic!
Ive got a lovely old stock Mazda which does this, that I paid a lot of money for NOS, and didn’t identify the issue until after the warranty expired 
Both triode sections work fine on their own.
And to be fair, it isn’t an issue for some applications, eg V1 of 5F6A / JTM45, when used with an ABY box.

[lexluthier72]

I think it was simply the tube. The shield was insurance.

Your original post indicated you replaced the 12AX7. Your fix ended up being a new 12AX7 (ECC83s) and a tube shield. I would be interested to know if the fix was the ECC83s, the tube shield, or the combination. Does the ECC83s fix the problem without the tube shield? If it does not, does the tube shield fix the problem on any of the other tubes you tried?

[lexluthier72]

THIS. I tried the JJ, which has an internal shield between the 2 sections at the recommendation of another electronics guy. It worked.

How a bad tube make "my volume pot does not shut off all the way. ? 

I have no idea what the mechanism is that cause the problem, but I can attest that there’s a unusual 12AX7 failure mode which results in signal applied to one of its triode sections also appearing in the other section. As if by magic!
Ive got a lovely old stock Mazda which does this, that I paid a lot of money for NOS, and didn’t identify the issue until after the warranty expired 
Both triode sections work fine on their own.
And to be fair, it isn’t an issue for some applications, eg V1 of 5F6A / JTM45, when used with an ABY box.

[pdf64]

Dozens of 12AX7 designs don’t have such a shield, yet don’t have crosstalk either. In fact I got several apparently identical Mazdas, only the one has that issue. The electrode structures seems pretty similar to Mullard.

[astronomicum]

Latole, how are any of your responses helpful?

I think it was simply the tube. The shield was insurance.

I think...? The shield was...? Do you think it was insurance or you know it was?

[shooter]

there might be yet another maybe;


the pressure from the shield is just enough to fix a bad "pin to socket seat" keeping the sloppy pin/seat from "radiating" signal