[_Knighthawk_]

very nice work.
perhaps new 2.7k and 25/25 on cathode

I can give that a try. I have meetings for the next couple hours but I'll jump on this asap.

 

[Alan Small]

this is my power cap bleeder...the resistor keeps the pop(which can be startling and cause a hand reaction that brings a shock) and fast draining to a minimum

 

[_Knighthawk_]

very nice work.
perhaps new 2.7k and 25/25 on cathode

Replaced both. Same behaviour is occurring.

Primary symptoms:

1) My voltage reading on Pin 1 of V5 seems to be way out of whack. I believe I should be expecting ~270V but I'm seeing 390V to 460V (jumps around a lot on the multi-meter). As you can see from the image, it is receiving power B+2 power from the board via the 220K resistor. Resistor is good.

2) The voltage really jumps around quite a bit on pin 3. It ranges from 1.6 VDC to 2.8VDC. It should relatively stable (as it is on V1).

 

[_Knighthawk_]

this is my power cap bleeder...the resistor keeps the pop(which can be startling and cause a hand reaction that brings a shock) and fast draining to a minimum

I'm using the same resistor with a slightly different design.

 

[gtrguy]

Turn down the trem speed and depth (or use the footswitch jack). Does the voltage stabilize?

 

[Richard Gear]

Turn down the trem speed and depth (or use the footswitch jack). Does the voltage stabilize?

I find that I have to turn both up to max to get a somewhat stable reading.

 

[Richard Gear]

I have verified the 220K resistor more than once (I measure each resistor before it goes on the board but this doesn't mean I haven't made this mistake!).

I can verify that the lead from pin 7 originates from the correct location (continuity tested on completion and again now - I dot these as in the image below.

View attachment 471320

I can verify that there there is a 100k resistor connected to ground bus from lugs 2 and 3 of the (3M RA) speed pot.

Thanks for the drawings! They are bit clearer than the Fender ones I was using (pin 1 should be 270 V).

I know when I get a cathode bypass cap close to that 2.2M on top of the two 1M tremolo grid leaks it makes a brutal noise. Also, if you wouldn’t mind humouring me and taking a Q-tip with some rubbing alcohol and very throughly scrubbing the resin / flux trail going from your 10M to 100k resistor at the bottom of your LDR.

The 400+ going into the 100K / 10M doesn’t want to have any reason to jump to the wrong end of the 10M.

 

[_Knighthawk_]

Turn down the trem speed and depth (or use the footswitch jack). Does the voltage stabilize?

No. Having either pot at full or no spread has no effect on the issue.

 

[_Knighthawk_]

I know when I get a cathode bypass cap close to that 2.2M on top of the two 1M tremolo grid leaks it makes a brutal noise. Also, if you wouldn’t mind humouring me and taking a Q-tip with some rubbing alcohol and very throughly scrubbing the resin / flux trail going from your 10M to 100k resistor at the bottom of your LDR.

The 400+ going into the 100K / 10M doesn’t want to have any reason to jump to the wrong end of the 10M.

Done! At least as much as I can get off of there anyway.

I always marvel at how clean some of the boards are that you see online. Are they using fluxless solder?

 

[Richard Gear]

Done! At least as much as I can get off of there anyway.

I always marvel at how clean some of the boards are that you see online. Are they using fluxless solder?

Something had exploded in this puppy before I got it. I removed the board and every single component and then nuked the board several times with alcohol and straightened and cleaned and redressed every wire, lead, resistor etc. sheet after sheet of paper towel came off of the board brown and black. Years of dust and leakage and flux.

When you look at how close eyelets are together, it’s easy to see how even a sling or strand of wire or flux can transfer some voltage etc.

 

[Alan Small]

a full set of pics showing your entire good work, knighthawk, is porn for some of us...

 

[_Knighthawk_]

Something had exploded in this puppy before I got it. I removed the board and every single component and then nuked the board several times with alcohol and straightened and cleaned and redressed every wire, lead, resistor etc. sheet after sheet of paper towel came off of the board brown and black. Years of dust and leakage and flux.

When you look at how close eyelets are together, it’s easy to see how even a sling or strand of wire or flux can transfer some voltage etc.

Whoa! Now that's a job! And one of the reasons I have no current interest in being an 'amp tech'. I like to build them but that kind of work is HUGE! What would you charge someone for something like that? It's pretty much a full rebuild using the same parts.

 

[_Knighthawk_]

a full set of pics showing your entire good work, knighthawk, is porn for some of us...

Oh, I know exactly what you mean!
As requested...

 

[_Knighthawk_]

Incidentally, I swapped out the 220K and reflowed both sides of the connection (reseated the 10 meg as well).

Nothing new to report. Still screams at 2 on the volume pot and sounds like I'm tuning in a top 40 station from Neptune.

Edit: On the upside. Channel 1 sounds pretty much like ti should.

 

[Alan Small]

may be off base here.....you describe what could result from a reversed feedback loop...unsolder the 820R running from the speaker jack tip(where yellow meets green) to the post pi network and listen for a difference....cant hurt to try...if it is improved then switch the speaker jack wires(the green and black) from the output tranny and rehook the feedback loop(the 2nd channel has an extra triode in use and the signal is inverted from the normal channel).
this should not affect the V4 pin 1 voltage issue....still..

 

[Richard Gear]

Whoa! Now that's a job! And one of the reasons I have no current interest in being an 'amp tech'. I like to build them but that kind of work is HUGE! What would you charge someone for something like that? It's pretty much a full rebuild using the same parts.

Thanks man. I honestly did this for myself. For my own mental health I needed to eliminate all possibility of board voltage and general dirt before I started doing my own stuff.

Whoever was in there before did solid work. Changed out the bypass and filter caps etc. But I have wanted this amp for a LONG time and it’s satisfying to do a full clean and reorganize.

before:

you can see a layer of dust and dirt from decades of operation and possibly sitting on a bench for a while etc.

Now:

If I were to do this for someone else, I’d probably charge a couple hundred because anything with reverb or with more stuff would be a lot longer to learn and to reset etc.

Your work on your amp is beatiful. I’m a fan of those Vishay resistors. They look the part even integrated into an older amp!! Don’t give up. Just keep trouble shooting and it will be something simple that we’ve all overlooked.

but the pics really do help us understand where to look etc. I’m with @Alan Small in appreciating the beauty of good work and new ideas.

 

[_Knighthawk_]

Thanks man. I honestly did this for myself. For my own mental health I needed to eliminate all possibility of board voltage and general dirt before I started doing my own stuff.

Whoever was in there before did solid work. Changed out the bypass and filter caps etc. But I have wanted this amp for a LONG time and it’s satisfying to do a full clean and reorganize.

before:

you can see a layer of dust and dirt from decades of operation and possibly sitting on a bench for a while etc.

Now:


If I were to do this for someone else, I’d probably charge a couple hundred because anything with reverb or with more stuff would be a lot longer to learn and to reset etc.

Your work on your amp is beatiful. I’m a fan of those Vishay resistors. They look the part even integrated into an older amp!! Don’t give up. Just keep trouble shooting and it will be something simple that we’ve all overlooked.

but the pics really do help us understand where to look etc. I’m with @Alan Small in appreciating the beauty of good work and new ideas.

That is one sweet amp, dude. I completely get why you would invest the time if it was on your wish-list. Congrats on the find and on the work you invested. I bet it sounds sweeeet!

Thank you for the kind words and good eye on the Vishays!!! Very impressive. I like 'em. They don't look quite as cool as the vintage carbon comps but they're reliable, in spec (always +/- 3 or 4%) and really quiet.

 

[_Knighthawk_]

may be off base here.....you describe what could result from a reversed feedback loop...unsolder the 820R running from the speaker jack tip(where yellow meets green) to the post pi network and listen for a difference....cant hurt to try...if it is improved then switch the speaker jack wires(the green and black) from the output tranny and rehook the feedback loop(the 2nd channel has an extra triode in use and the signal is inverted from the normal channel).
this should not affect the V4 pin 1 voltage issue....still..

I'm willing to give this a try but I'm not sure exactly how to do what you are suggesting.

You want me to unhook the 820R and hook the speaker jack directly it into the 47ohm/22k ohm/.1uf shunt cap junction?

Question: Would that not invert channel 1?

 

[_Knighthawk_]

Just keep trouble shooting and it will be something simple that we’ve all overlooked.

Update: Breakthrough! And it WAS something simple!

The volume surge in the volume channel was caused by a bad tone cap. On a whim (to rule it out), I removed it and f'ing voila!!! Volume surge gone!

It's pretty funny that the $3000 amp build can get side-swiped by the $3 capacitor!

Anyway, so, now to get these voltages under control and tweak the ground scheme to kill some of this blasted Deluxe Reverb hum. I have had success with this last on my Vibroverb builds (same circuit) so it's just a matter of arm wrestling and little tweaks to get this right. That said, I'm all ears if anyone has any ground scheme suggestions.

You can see what I have done here: power amp ground, preamp ground bus, reverb ground to reverb pedal ground lug, etc. Always open to new ideas.

 

[Alan Small]

I'm willing to give this a try but I'm not sure exactly how to do what you are suggesting.

You want me to unhook the 820R and hook the speaker jack directly it into the 47ohm/22k ohm/.1uf shunt cap junction?

Question: Would that not invert channel 1?

no. simply disconnect the yellow feedback wire from the tab on the jack that shares the green output tranny wire: this is the feedback loop that calms down the output signal by cancelling out some distortion.