Peavey Donor amp build

[dcribbs1412]

Got a little more done...getting closer to power time. Keeping it simple
for start-up. I may go back and add relays and FET later

http://i1018.photobucket.com/albums/af3 ... ean016.jpg
http://i1018.photobucket.com/albums/af3 ... ean015.jpg
http://i1018.photobucket.com/albums/af3 ... ean013.jpg
http://i1018.photobucket.com/albums/af3 ... ean010.jpg

My concern is the bias circuit, not real clear on it...using
the HV taps I've seen a few different ways.I have it like the peavey layout
from Bob-I not real sure about the wiring of it. As in does 1 leg of the secondary go to the B+ the other to standby switch along with choke?
Any suggestions are greatly appreciated

Thanks

Darin

[M Fowler]

Man that is looking good.

Got one question about that plated welded to the bottom of the transformer didn't the welding process destroy the windings?

Mark

[dcribbs1412]

Man that is looking good.

Got one question about that plated welded to the bottom of the transformer didn't the welding process destroy the windings?

Mark

Thanks Mark
well I don't think so...it was like that originally same with OT
both have plate welded to bottom(decent looking bead). I think it was made in Canada(stickers on back say) also one sticker has a "burned in" 85 on it.
I think these were built starting in 84. I hope the iron is good...


Any ideas on my bias concerns?

Thanks
Darin

[M Fowler]

My concern is the bias circuit, not real clear on it...using
the HV taps I've seen a few different ways.I have it like the peavey layout
from Bob-I not real sure about the wiring of it. As in does 1 leg of the secondary go to the B+ the other to standby switch along with choke?

Darin what you have is good. The rectified voltage goes to the standby switch then onto main filter cap where one leg of the choke and OT also connect there.

Mark

[dcribbs1412]

My concern is the bias circuit, not real clear on it...using
the HV taps I've seen a few different ways.I have it like the peavey layout
from Bob-I not real sure about the wiring of it. As in does 1 leg of the secondary go to the B+ the other to standby switch along with choke?

Darin what you have is good. The rectified voltage goes to the standby switch then onto main filter cap where one leg of the choke and OT also connect there.

Mark

Thanks Mark
I think I understand a little more now what needs to go where...
its the little things that cornfuse me the most...but I feel I'm still learning.
hope to post some more progress soon.
Appreciate your time

Darin

[dcribbs1412]

Got it wired...tested with limiter...no shorts
plugged in some tubes and no bias adjustment.
voltages are really low
problem with bias? I only have 200V going in to bias circuit
pics of wiring...
http://i1018.photobucket.com/albums/af3 ... ean023.jpg
http://i1018.photobucket.com/albums/af3 ... ean022.jpg
http://i1018.photobucket.com/albums/af3 ... ean019.jpg
http://i1018.photobucket.com/albums/af3 ... ean018.jpg

any suggestions are greatly appreciated

Darin

[Bob-I]

Got it wired...tested with limiter...no shorts
plugged in some tubes and no bias adjustment.
voltages are really low
problem with bias? I only have 200V going in to bias circuit
pics of wiring...


any suggestions are greatly appreciated

Darin

It seems to me that some versions of this amp used a bridge rectifier. You might check the original board.

I've built 3 of these, I think 2 used bridge rectifiers, but then again sometimes I don't remember things all that... What was I talking about?

[dcribbs1412]

Got it wired...tested with limiter...no shorts
plugged in some tubes and no bias adjustment.
voltages are really low
problem with bias? I only have 200V going in to bias circuit
pics of wiring...


any suggestions are greatly appreciated

Darin

It seems to me that some versions of this amp used a bridge rectifier. You might check the original board.

I've built 3 of these, I think 2 used bridge rectifiers, but then again sometimes I don't remember things all that... What was I talking about?

Thanks Bob
not sure but looking at the schem on page one of this thread
the two taps go in the center of the diodes,with one .01 cap across.One end going to ground and the other to the cap B+? Does that sound right?
pic of my setup which looks wrong

[Bob-I]

Your description is correct, and yes your setup looks wrong. That would explain the low voltages.

[dcribbs1412]

Thanks Bob
trying to wrap my head around this
would something like this work?
Or do the diodes need to be oriented different.
I found Visio...
Appreciate your time

Darin

[Bob-I]

Looks correct to me. Hopefully you'll get some more eyes on this just to be sure.

Of course use standard power up practices, limiter, no tubes, you know the drill.

[dcribbs1412]

Looks correct to me. Hopefully you'll get some more eyes on this just to be sure.

Of course use standard power up practices, limiter, no tubes, you know the drill.

Thanks Bob
I moved the Sec taps to the middle of the diodes and no go...
same low voltage.I guess I'll remove all the .01 caps and try it like the visio drawing, not sure if the single .01 cap placement matters...(peavey schem
and JCM900 are in different places)

Darin

[tictac]

Here's how to get the -bias from the B+ tap...

[dcribbs1412]

Thanks guys
got the bias working...
problem now is the voltages are low
seems the PT has a low power tap 260V which is what I'm getting(254)
looking at the original power board the 2 HV taps look normal
but the HV CT tap doesn't seem to go to ground...looks like it connects to main filter caps. Would this up my voltages?...unless I'm way off. Any suggestions are appreciated

Darin

[Bob-I]

Cap off the low voltage tap and connect only the high voltage tap to the bridge rectifier. Nothing from the PT secondary taps get grounded.