Bias voltage drops when rest of amp is conneceted.

[RomesInMil]

Hello again my helpful friends.
So I built a Hoffman Bassman, mine is Bassedman.
Had it working, got the tubes right as I was tailoring it for bass.
Used a hammond organ in series with another for the proper HT, was feeling myself.
Got confident added a LFB on a single valve, found input jacks that switch non-audio.
So I thought HEY, lets make the second input guitar and ground some caps on guitar input and remove the single valve LFB.
Did not work, got frustrated so took a break.

During that break a White Claw got spilled on the TF and TF chassis during... adult time, and even though not plugged in made the fucker shoot out OL voltage. Fried my power board. My dumbass decided to lazy and ordered 500v caps forgetting that when just the rect is plugged in it's gona go higher. Fried those.

Got everything working again except, and I have tried all I could think of...
The bias supply sends a spirted -71. Great. Now when the rest of the amp is powered on, it drops to -9 and nothing I tried helps.

Anyone have any ideas? I promise to pass it forward.
Thanks.

[SoulFetish]

Ive seen bad output tubes cause that before. Also, leaky coupling caps can cause a large DC discrepancy in the bias supply, but you probably wouldn’t need to install the tubes to see it

[pdf64]

... Used a hammond organ in series with another for the proper HT, was feeling myself.

I don't understand what is meant by any of that?

Got confident added a LFB on a single valve

Please define unusual acronyms, what is a 'LFB'?

During that break a White Claw got spilled on the TF and TF chassis during...

I guess White claw is a beer?
What is a 'TF'?

[Stevem]

Communication skills are lacking here it seems, not just tube electronic knowledge.

[Phil_S]

I guess White claw is a beer?
What is a 'TF'?

White Claw is hard seltzer. Fizzy water with sugar, flavoring, and beer level alcohol. https://en.wikipedia.org/wiki/White_Claw_Hard_Seltzer

Can't help with "TF" except to say, I don't think it is the last two letters of WTF...

[jabguit]

I guess White claw is a beer?
What is a 'TF'?

Can't help with "TF" except to say, I don't think it is the last two letters of WTF...

trans former?

[maxkracht]

trans former?

Yes. Hammond organ in series with another means the power supply (TF) of one hammond organ and another section of another, or the same, organ for the rest of the amp. I don't recognize the black chassis. I guess all the shorthand we use makes it seem like it's common practice to abbreviate any and everything. If he used PT instead of TF most of us would have got it without thinking.

Used a hammond organ in series with another for the proper HT, was feeling myself.

That's not what they mean by keeping one hand in your pocket, adult time is what got you into this mess

I would suggest providing a schematic that includes the power supply and all of your modifications. Also might want to clean the area of the spill thoroughly with rubbing alcohol.

[nuke]

I can see there's a Hoffman board, but I can't make heads nor tails of what all is going on there. The wiring is quite complex and not possible to follow from a photo.

I can see two "vintage" Astron yellow capacitors with green ink markings and blue-epoxy ends, as are used in Fender tweed era amps. I can garantee you, those are bad. Beyond that, I can't really offer anything.

[sluckey]

That's not a Hoffman board. This guy posted early Monday morning and has not been back on the site since then.

[RomesInMil]

Oh I did not get any e-mails regarding replies! I am so sorry to everyone who botherd!

[RomesInMil]

AGAIN I AM SO SORRY I DID NOT REALIZE THERE WERE RESPONSES!

Ive seen bad output tubes cause that before. Also, leaky coupling caps can cause a large DC discrepancy in the bias supply, but you probably wouldn’t need to install the tubes to see it

I replaced the caps, I am measuring pin 5 of the 6L6 on an empty socket.

I would suggest providing a schematic that includes the power supply and all of your modifications. Also might want to clean the area of the spill thoroughly with rubbing alcohol.

On it!

I can see two "vintage" Astron yellow capacitors with green ink markings and blue-epoxy ends, as are used in Fender tweed era amps. I can garantee you, those are bad. Beyond that, I can't really offer anything.

They are NOS, tested and used in my Champ clone, Tubi McTube face and sound great!

[RomesInMil]

So as far as mods, the bias circuit is housed in the PT chassis. I did use a XLR to connect it to the main chassis when it worked. Got rid of that now, will use something simpler if and when I can figure out the drop.

Outside of that, the PT is no longer in series with another since the new Hammond PT is higher voltage as I mentioned at first.

Oh, the cassis is just a random one I found, to make everything fit, the res caps are mounted on terminal strips in series and hanging off the main board.

[R.G.]

(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.

[RomesInMil]

Just a bump for the previous responses, again I did not know people were replying I now have e-mail notifications turned on.

[martin manning]

Just a bump for the previous responses, again I did not know people were replying I now have e-mail notifications turned on.

But AFAIK you will still not be getting e-mail notifications as that feature is broken.