Hoffman Princeton Reverb (Why Sans Headroom & Other Questions)

[AHeck]

I just finished up a build and i'm not getting the quitar noises I had expected.  I'm not getting anything clean to speak of.  Perhaps someone might be able to help.  I'm looking at the low plate voltages on V1 and V4's bouncing voltage.  I should start there (with voltages) and anything that might be requested will be supplied.  Thanks
V1: P1-70.5/P3-2.2/P6-61/P8-2.3
V2: P1&6-400/P3&8-7.1
V3: P1-149/P3.96/P6-150/P8-.99
V4: P1-220-256 bouncing/P3-2.8/P6-150/P8-2.8
V5: P3-413/P4-400/P8-.022
V6: P3-411/P4-402/P8-.022

[sluckey]

Measure the voltages at points A, B, C, and D. V4-A voltages should be bouncing. That's the tremolo. Turn the trem off with the footswitch and the voltages will be steady.

Post some hi-rez pics. If there are no wiring errors or incorrect component values, your amp should sound like this...

[AHeck]

A-416
B-408
C-309
D-216
I appreciate your time, I'll be posting photos directly.

[sluckey]

Put a good 12AX7 in V1 socket.

[shaun]

I'm am possibly the least expert person in the forum, but I see you have good B+ voltage on V3, so it seems unusual you'd have low B+ on V1. That might be a symptom of the problem and is where I'd look first.

V1: P1-70.5/P3-2.2/P6-61/P8-2.3
V2: P1&6-400/P3&8-7.1
V3: P1-149/P3.96/P6-150/P8-.99

[AHeck]

i've had two good 12ax7s and a good 12ay7, they all were wanky.  i'm wondering if im not getting good contact from the socket for V1

[AHeck]

I would add:  Why do you say that about V1 so not so seem ungrateful....

[sluckey]

I suggested a new 12AX7 because the voltages on V1 are wrong. I was thinking maybe you had used a 12AU7 or 12AT7. V1 voltages should be the same as V3 voltages. What is the voltage on V1 pins 2 and 7?

A hi-rez pic that shows V1 socket and the board just might reveal something.

[2deaf]

V1 voltages are consistent with a 12AX7 that doesn't have a ground reference for its grids.  Temporarily ground one of the grids and see what happens to the plate and cathode voltages.

[DummyLoad]

V1 voltages are consistent with a 12AX7 that doesn't have a ground reference for its grids.  Temporarily ground one of the grids and see what happens to the plate and cathode voltages.

input jacks probably wired wrong - not seeing 1M grid leaks? 68K grid stoppers not connected correctly?


--pete

[AHeck]

I’m having a ignorance problem with posting pictures. All of my files are too big. Trying to figure out how to fix that, but I think I have mis-wired my input jack.  I’ve got 1M tip to ground jumped to switch.  That might be a problem.

[sluckey]

Check the voltages on V1 pins 2 and 7. What are the two voltages?

Then check the grid resistances with your ohm meter. Turn power off. Do this with no cable plugged into the input jacks and the VOL pot set to zero. Connect one probe to chassis. Connect the other probe to V1 pin 2. Should be 33K. What have you? Now move the probe from V1 pin 2 to V1 pin 7. Should be zero. What have you?

[AHeck]

33K and 0 ohm

[AHeck]

The Input Jack

[PRR]

I’m having a ignorance problem with posting pictures. All of my files are too big.

https://el34world.com/Forum/index.php?topic=464.0

[AHeck]

I'm sorry, I'm trying to work on a Mac and have no clue how to resize photos, or export or basically anything.  Imma get a "Computers For Idiots" book and in a few weeks maybe I can get y'all a picture or two.

[2deaf]

I'm sorry, I'm trying to work on a Mac and have no clue how to resize photos, or export or basically anything.  Imma get a "Computers For Idiots" book and in a few weeks maybe I can get y'all a picture or two.

Open the picture in Preview.  Click on Tools.  Click on Adjust Size.  Adjust size.  Click on Show Inspector to see the resulting size.

[PRR]

....Open the picture in Preview.  Click on Tools.  Click on Adjust Size.  Adjust size.  Click on Show Inspector to see the resulting size.

Same advice in more detail:

Apple docs:
https://support.apple.com/guide/preview/resize-rotate-or-flip-an-image-prvw2015/mac

Apple fans tip site:
https://appletoolbox.com/adjusting-image-sizes-preview/

[AHeck]

The Board

[AHeck]

HA!

[AHeck]

Thanks so much for all the help with getting these fool pictures up.  Can anyone see anything wrong? 
I got on the scope and after the phase splitter, I'm getting plenty of negative signals at the .1uf coupler coming off of V4 pin 6, but no real positive signal at the .1uf coming off of V4 pin 8 (full disclosure, PIN numbers might be reversed but definitely getting a lot of neg and little pos). 
Another observation is that when I scope the signal at the 2.7K resistor that catches the NFB (which I have tied to the 8 ohm tap on a 3PST switch at the output), the signal clips with very, very little prodding, disturbingly little prodding.
Again I'm very thankful for this forum and the experience y'all are willing to share.

[sluckey]

I only see one pic of the preamp end of the board. Where's the rest of the amp? Looks like you did a reverse build?

[AHeck]

I did do a reverse build, yessir.  I’ll put up various angles over the whole.  Somehow I thought we were looking just at V1 and ground reference issues, apologies.  I can also put the scope to it if you need and post those images as well.  Thanks

[sluckey]

Can't see any ground connections in that pic. I know pin 2 connects to the input jack and I saw the ground connection for that. But pin 7 should go to the VOL pot and I don't see that. However, your resistance readings indicate correct resistance readings for pins 2 and 7.

You still have not posted voltage readings for pins 2 and 7.

[AHeck]

0V on either  pin2 or pin7.

[sluckey]

It all looks good. The only thing left is the tube socket.

Try this. Use a gator clip test lead to connect pin 2 directly to chassis. Gator clip directly on the tube socket. Do pin 1 and pin 3 voltages go to normal? If not, replace the socket. Belton would be my choice.

[AHeck]

so after directly connecting pin 2 to chassis via clip lead, the voltages of pin 1 and 3 stayed consistently not right.  What does that mean?  I'm not sure what happened and what changing the socket might fix and how to not repeat whatever happened.  Thanks.