Bias voltage drops when rest of amp is conneceted.

[R.G.]

If the issue is important enough to ask in a forum, it's important enough to remember to check the forum periodically, I think.

Edit: I forgot - how's that voltage testing going?

[RomesInMil]

If the issue is important enough to ask in a forum, it's important enough to remember to check the forum periodically, I think.

Edit: I forgot - how's that voltage testing going?

I apologized, I was under the impression that I would be emailed when there were replies.

Currently I am rebuilding the bias circuit that is housed in the PT chassis, it's the only item that may have got whiteclawed that I have yet to replace.

[RomesInMil]

(1) Set up the transformer chassis the way that you get that healthy -71V of bias voltage. Measure and WRITE DOWN:
> the bias voltage, presumably still -71V
> the DC voltage on the first filter capacitor
>>> the AC line voltage across the transformer primary wires

(2) Turn off the AC mains and drain the filter capacitors down to 0V with resistors.

(3) Connect the rest of the amp that makes the voltages lower. Plug it in, turn on the AC. Measure and WRITE DOWN:
> the bias voltage, presumably lower now
> the DC voltage on the first filter capacitor
>>> the AC line voltage at the solder joints for THE TRANSFORMER PRIMARY WIRES
>>> the AC voltage before and after the switch
>>> the AC voltage before and after the fuse
>>> the AC voltage at the solder joints for the incoming AC line cord wires.

(4) Report those numbers back here.

Why: All the symptoms could be accounted for by some bad connection in the chain from the AC wall socket, through the line cord, through the fuse, through the switch, and through the transfomer. If one of those steps is high resistance, a bad solder joint, etc., it would explain the suddenly dropping voltage, and is a reasonable outcome of spilling adult beverages into the power section.

Ok, I have a couple showings this morning, ill report back thank you.

[RomesInMil]

(1) Set up the transformer chassis the way that you get that healthy -71V of bias voltage. Measure and WRITE DOWN:
> the bias voltage, presumably still -71V
> the DC voltage on the first filter capacitor
>>> the AC line voltage across the transformer primary wires

(2) Turn off the AC mains and drain the filter capacitors down to 0V with resistors.

(3) Connect the rest of the amp that makes the voltages lower. Plug it in, turn on the AC. Measure and WRITE DOWN:
> the bias voltage, presumably lower now
> the DC voltage on the first filter capacitor
>>> the AC line voltage at the solder joints for THE TRANSFORMER PRIMARY WIRES
>>> the AC voltage before and after the switch
>>> the AC voltage before and after the fuse
>>> the AC voltage at the solder joints for the incoming AC line cord wires.

(4) Report those numbers back here.

Why: All the symptoms could be accounted for by some bad connection in the chain from the AC wall socket, through the line cord, through the fuse, through the switch, and through the transfomer. If one of those steps is high resistance, a bad solder joint, etc., it would explain the suddenly dropping voltage, and is a reasonable outcome of spilling adult beverages into the power section.

Ok, I have a couple showings this morning, ill report back thank you.

OK here might be another clue, using a bulb limiter, I get surge when rectifier is plugged in, replaced the socket, same issue, replaced the 4AR5 same issue.....dont see obvious short.... voltage harness unplugged, is fine, plugged in its fine, as soon as the rect is plugged in surge.... are my protection diodes fucking with it?

[RomesInMil]

Guessing its the harnesses. Basically rebuilding it. Had to try the non-audio switches ......

[R.G.]

Any chance of getting the voltages measured?

[jabguit]

OK here might be another clue, using a bulb limiter, I get surge when rectifier is plugged in, replaced the socket, same issue, replaced the 4AR5 same issue.....dont see obvious short.... voltage harness unplugged, is fine, plugged in its fine, as soon as the rect is plugged in surge.... are my protection diodes fucking with it?

4AR5? maybe 5AR4?

[RomesInMil]

Any chance of getting the voltages measured?

IT WAS THE HARNESS!!!
Getting -51 at pins
Happened to have order this guy from temu a while ago, works much better than the smaller ones and got rid of the makeshift plastic housing I needed to make it work prior!

Thank you for the help all the same. Don't change!

4AR5? maybe 5AR4?
[/quote]

Does it feel good to correct someone for a obvious and unimportant typo? I hope your day was a little better.

[jabguit]

4AR5? maybe 5AR4?

Does it feel good to correct someone for a obvious and unimportant typo? I hope your day was a little better.
[/quote]


wow! I guess spelling, grammar and logistics have no place on this forum......

cheers,

[RomesInMil]

4AR5? maybe 5AR4?

Does it feel good to correct someone for a obvious and unimportant typo? I hope your day was a little better.

wow! I guess spelling, grammar and logistics have no place on this forum......

cheers,
[/quote]
It's not black and white like that.
Ask yourself, does it need to be corrected to be understood?
Otherwise why am I doing it and for whom?

[SoulFetish]

4AR5? maybe 5AR4?

Does it feel good to correct someone for a obvious and unimportant typo? I hope your day was a little better.

wow! I guess spelling, grammar and logistics have no place on this forum......

cheers,

It's not black and white like that.
Ask yourself, does it need to be corrected to be understood?
Otherwise why am I doing it and for whom?
[/quote]

Romes, even though I didn't make the initial spelling error, I didn't read jab's correction as he meaning to contentious. There are so many different tube types and oddballs that people will use in home builds for one reason or another, I didn't immediately know you meant 5AR4. The first Number in North American tube designation identifies the heater voltage. The most common in guitar amps is 5V, 6.3V, and 12V, but there are so many different heater voltages that were commonly used.
Most people here who offer corrections are just trying to be helpful. Most of this is a matter of science and we're all trying to get it right. No need to take it personally.
I really appreciate those who take the time to read through my posts and offer insight and possibly correct something if I get it wrong. They are doing me a favor. I don't want to be misinformed or put out information that is incorrect.

[R.G.]

Let it go, guys. It's clear that all the blocks are not stacked perfectly straight.