Princeton Reverb Volume issue - Help?

[Imntgrumpy]

Hey guys,

Re:  Hoffman Style Princeton Reverb w/mid and dwell mod.

I thought I was finished with repairs on this amp.  Unfortunately, something new crept in.  I just finished re-tubing and re-capping this amp.  Also, had to change the 10kl bias pot to 50kl in order to achieve 30ma bias.  Changed out (suspect) volume pot with new 1M.

Here's the issue;  vol, treb, mid, & bass all set to zero - still hear guitar.  Turn vol up - no increase in volume.  Turn treb, mid and bass up, now vol will increase.  However,  it will still never go to full silent when set to zero.

Obviously, somehow the guitar signal is getting through.  I'm just not seeing where the problem is. 

Any Ideas would be appreciated.

Thanks,
Jim

[sluckey]

Here's the issue;  vol, treb, mid, & bass all set to zero - still hear guitar.

How loud is the guitar with all knobs set to zero? Did you use shielded cable for the connection between the volume pot and V1 pin 7? Is the pot ground buss securely grounded at the input jack? Is the input jack tightly connected to the chassis? Is the input jack an uninsulated switchcraft type?

Use a gator clip test lead. Connect one end to chassis. Carefully connect the other end to V3 pin 7 directly at the tube socket. Does this completely kill the guitar? If so, move the gator clip to V1 pin 7 directly at the tube socket. Does this completely kill the guitar?

[Imntgrumpy]

Here's the issue;  vol, treb, mid, & bass all set to zero - still hear guitar.

How loud is the guitar with all knobs set to zero? Did you use shielded cable for the connection between the volume pot and V1 pin 7? Is the pot ground buss securely grounded at the input jack? Is the input jack tightly connected to the chassis? Is the input jack an uninsulated switchcraft type?

Use a gator clip test lead. Connect one end to chassis. Carefully connect the other end to V3 pin 7 directly at the tube socket. Does this completely kill the guitar? If so, move the gator clip to V1 pin 7 directly at the tube socket. Does this completely kill the guitar?

How Loud? - like a speakerphone at 50%
Shielded Cable - Yes
Ground Buss - Hoffman style - will re-check for tight connections.
Input jack - Tightly connected, uninsulated switchcraft type.

Will try Gator clip test when I get home.

Thanks

[Imntgrumpy]

Here's the issue;  vol, treb, mid, & bass all set to zero - still hear guitar.

How loud is the guitar with all knobs set to zero? Did you use shielded cable for the connection between the volume pot and V1 pin 7? Is the pot ground buss securely grounded at the input jack? Is the input jack tightly connected to the chassis? Is the input jack an uninsulated switchcraft type?

Use a gator clip test lead. Connect one end to chassis. Carefully connect the other end to V3 pin 7 directly at the tube socket. Does this completely kill the guitar? If so, move the gator clip to V1 pin 7 directly at the tube socket. Does this completely kill the guitar?

Sluckey,


Before I fry myself or the amp just want to check that the Gator clips if first connected to chassis ground then  "V3 Pin 7"  then move to "V1 Pin 7".


Jim

[sluckey]

Sluckey,

Before I fry myself or the amp just want to check that the Gator clips if first connected to chassis ground then  "V3 Pin 7"  then move to "V1 Pin 7".

Jim

You in the deep end of the pool now! Be careful.

[Imntgrumpy]

Sluckey,

Before I fry myself or the amp just want to check that the Gator clips if first connected to chassis ground then  "V3 Pin 7"  then move to "V1 Pin 7".

Jim

You in the deep end of the pool now! Be careful.

OK.  Guitar signal goes quiet at V3Pin7.  Moved to V1Pin7 still hear guitar.


 


Bad tube socket?  Bad Ground?  I'm lost.

[Imntgrumpy]

I can't imaging what is causing this volume issue.  I've noticed that when I rotate the volume pot just a few degrees from zero, the volume will drop and the sound takes on a reverb/metallic quality.   I'm testing the amp without the reverb tank connected, so it can't be the reverb tank. 

Looks like I'm going to have to pull the board.  I need to be sure that all underboard wires are properly installed. 

[sluckey]

I don't see any underboard jumpers that would cause this. Check ground connections. You do have a 220K resistor mounted on the reverb return jack and connected to ground? Plug in the reverb tank and just set the reverb pot to zero. Post some hi rez pics for us to look at.

Try this... Temporarily connect a 20µF (can be any value between 10 and 50) between ground and your node D cap. Any better?

[HotBluePlates]

... Princeton Reverb ...

Here's the issue;  vol, treb, mid, & bass all set to zero ...  Turn vol up - no increase in volume.  Turn treb, mid and bass up, now vol will increase. ...

Wanted to chime in separately to say what is described in the text above is normal behavior for a blackface amp.  When all the tone controls are set to zero (especially when a separate Mid control is available), there will be essentially no-volume.  And it won't increase again until you turn the tone controls up again.

This is separate from your "volume won't go to zero" issue.  I think that's either a bad ground (as Sluckey mentioned) or a pot whose wiper doesn't go all the way to the ground end.

[Imntgrumpy]

OK.  After all the tribulations over this issue.  It was most likely the replacement tube that I installed into the first pre-amp position.  Apparently the JJ ECC803s doesn't like being there.  As soon as I changed to a standard ECC83 the amp performed beautifully.

Hey,  Live and learn.  Thanks to all for your input and advice.

On to the next project.

[HotBluePlates]

...  It was most likely the replacement tube that I installed into the first pre-amp position.  Apparently the JJ ECC803s doesn't like being there.  As soon as I changed to a standard ECC83 the amp performed beautifully. ...

Wow.  Thanks for reporting back & letting us know it was the tube!  Do you think it was cross-talk between section, that was fixed by using a different tube?