Princeton Reverb build Volume issue??

[Govmnt_Lacky]

Good day Community!

Odd issue with a Princeton Reverb build. Was able to complete it and bias it up just fine. Actually sounds pretty good for the most part.

Some context...

Iron: PT-290AX PT, 1760E OT
Tubes: All JJ... matched 6V6S for Output tubes. 5U4GB for Rectifier

Problem I am having is odd. I am still getting output even when the Volume pot is completely CCW. As I turn up the Volume pot, at about 1-2 I get a slight dip in output. After about the 2 setting, the volume acts normally. Previous PRs that I have worked on had NO output when the Volume pot was full CCW.

Online research has proven to be of no use (to this point)

Reaching out to you fine folks to see if you may have an idea or a place to start.

Cheers and Thanks in advance!

[Jon Snell]

Ensure the cathode return point for the pre amp valves and the bottom of the pot are the same ground point. Otherwise odd things will happed, just as you have described.

[Govmnt_Lacky]

Ensure the cathode return point for the pre amp valves and the bottom of the pot are the same ground point. Otherwise odd things will happed, just as you have described.

Verified that the Cathode returns and the actual pot casings are all connected to Ground. Also verified that when the Volume pot is full CCW that I am getting about 1 ohm between V1 Pin 7 and Ground.

[mozz]

Try grounding that pin, you should get no signal what so ever.

[Jon Snell]

They must connect to the same ground, not six inches away on the same wire.
If all grounds go to the same point, you will have no signal on zero.

[g1]

Have you tried a different tube there?

[Govmnt_Lacky]

Try grounding that pin, you should get no signal what so ever.

Was gonna try this next. Thanks!

They must connect to the same ground, not six inches away on the same wire.
If all grounds go to the same point, you will have no signal on zero.

How exactly would one tie the casing or a lug to a pot directly to a ground point on a circuit board WITHOUT wire in an amp build??

They must connect to the same ground, not six inches away on the same wire.
If all grounds go to the same point, you will have no signal on zero.

I did manage to find one single article from years ago about someone who saw strange Volume/output issues on a PR and it turned out to be bad JJ preamp tubes. This will be my last option. Cheers!

[g1]

I did manage to find one single article from years ago about someone who saw strange Volume/output issues on a PR and it turned out to be bad JJ preamp tubes. This will be my last option. Cheers!

The volume control is in between the 2 halves of the 12AX7. If there is crosstalk between the 2 halves you will get some volume leakage.

[Jon Snell]

"How exactly would one tie the casing or a lug to a pot directly to a ground point on a circuit board WITHOUT wire in an amp build??"

I am sorry but you don't seem to nderstand what I am saying.
I will draw a circuit to show you.
Firstly incorrect wiring causing uvolts of signal at all times.

Secondly zero signal on vol control how it should be wired.

I trust you now grasp the meaning of wiring ground points. Just that short length of ground wire going to the wrong point causes signal current to flow into the grid of U1A which will caise break through at all times.

[Govmnt_Lacky]

Well, I have tried grounding Pin 7 of V1 directly (bypassing the Volume pot wiper) and I still get signal bleed. Also tried a different 12AX7 in the V1 spot (non JJ tube known good). Still getting signal bleed. Verified ALL of the Grounds and they are all good. Never seen this before on a PR.

[Helmholtz]

Please post the schematic here.

[Govmnt_Lacky]

V1 in this build is 12AX7. Output tubes are 6V6S. All JJ tubes except for V1 which is an EH. Previously had JJ in V1 with same issue.

[Chuck H]

That is NOT a link to the schematic. It's a link to a site that is very general and you can then choose to go to amplifier related content AND THEN look for Princeton Reverb information AND THEN look for a schematic. Sorry dude. THat's not much effort put into the request for someone offering to help. So...

As far as I can tell the Princeton Reverb schematic on the robrobinette site is the AA1164 with the 5u4 rectifier. That schematic from Schematic Heaven isn't readable so I'm linking the AA1164 gz34 version. It's the same other than the rectifier type.

https://schematicheaven.net/fenderam...z34_aa1164.pdf

[Chuck H]

Also...

It doesn't seem likely that you would have the volume pot grounded to the top of any cathode circuit as you would almost have to ignore the layout and do it intentionally. But you may have signal bleed because of incorrect power supply wiring. If there's no filter properly wired to the preamp high voltage node then signal from the first triode won't be decoupled in the power supply.

A ground problem always seems like the more likely culprit but you report that you have checked grounds and they are proper and good.

[Govmnt_Lacky]

Also...

It doesn't seem likely that you would have the volume pot grounded to the top of any cathode circuit as you would almost have to ignore the layout and do it intentionally. But you may have signal bleed because of incorrect power supply wiring. If there's no filter properly wired to the preamp high voltage node then signal from the first triode won't be decoupled in the power supply.

A ground problem always seems like the more likely culprit but you report that you have checked grounds and they are proper and good.

I initially linked the wrong thing. I have corrected it with the proper schematic (which does indeed have the 5U4 rectifier which is in this build.

As I stated before, I have checked all of the grounds. All of them check good all the way back to the chassis ground. Also, I have bypassed the Volume pot all together and directly grounded Pin 7 of V1 and I am still getting bleed through volume.