Autoformer

[sdman]

Need an autoformer for an Peavey Musician/400GH.

Used one would be ok.

Peavey Parts doesn't have it anymore

sdman@cableone.net

[Enzo]

None here.

But I would be remiss if I did not ask what is wrong with yours.  If the amp puts out DC, that transformer will naturally act as a dead short across it and blow fuses.

The amp will function without it.  So you can connect the output of the amp directly to a speaker.  Does that work?   The impedance switching would no longer work, and an 8 ohm load would be 3db less loud, but otherwise the amp OK.

[sdman]

Hi,

For some reason the guy connected 120vac to the output, he said it was accidental.

Thanks for the reply.

Sam

[J M Fahey]

Then more than the output autoformer the power amp stage must be blown to pieces .

External 80V RMS must have shred them to ribbons, ignited the PCB, etc.

I´d first repair the power amp (if possible) and later worry about the autoformer.

[Enzo]

Exactly.  Fix the amp first, without the transformer.  THEN worry about it when the amp is 100%.


How on earth can you connect 120vAC to the output?  Who has 120vAC on the end of a speaker cord?

[sdman]

Yes, the power amp is repaired and is working fine.

Luckily it was just three outputs.

I expected worse myself, In fact I was reluctant to work on it.

Now if I can a autoformer to complete the job.

Sam

[Enzo]

So now that it is fixed, we still have determined the autoformer is bad?


I don't know if this fits, but when the amp goes to DC on the output, that autoformer looks like a dead short to the DC, and fuses blow.  But with AC applied - the amp output - it could be fine.


Test it:  apply some AC voltage to it from something.  Limit current in some way.  Now see if that AC comes out the remaining lead.

[J M Fahey]

So now that it is fixed, we still have determined the autoformer is bad?


I don't know if this fits, but when the amp goes to DC on the output, that autoformer looks like a dead short to the DC, and fuses blow.  But with AC applied - the amp output - it could be fine.


Test it:  apply some AC voltage to it from something.  Limit current in some way.  Now see if that AC comes out the remaining lead.

1) just checking, excuse me for being somewhat obsessive: did you already check amp has NO DC on its output and it can drive a speaker to loud (deafening) volume?
Without autoformer of course.

2) what exactly makes you think the autoformer is bad?

Thanks.

[Roly]

How on earth can you connect 120vAC to the output?  Who has 120vAC on the end of a speaker cord?

http://www.ozvalveamps.org/gowrong.htm

Scene 6
"I'm a Ginger Beer and I'm okay..."
{truly - you couldn't make this  :duh up}

[J M Fahey]

How on earth can you connect 120vAC to the output?  Who has 120vAC on the end of a speaker cord?

Believe it or not, it happened to me 

I sold a 200W PA powered mixer and matching sound columns to a then very famous Night Club , we're talking early 70's.

It had a cool "artist friends in your living room" atmosphere with people everywhere ... obviously trampling over speaker cables





so the club owner hired a local electrician to "hide those ugly cables inside the wall"  ... which he did, passing regular white parallel 16 ga through existing conduit.

He must have been real drunk  xP , no kidding, because somewhere along the path he mixing his wiring colours (all white, remember ) and connected 220V to the speaker line  :loco   :duh   :grr  :trouble
what he noticed as soon as he restored wall power , which he had cut to work.

This happened in a posh summer resort in nearby Uruguay, so I got an urgent call to go to Buenos Aires airport to pick a plane ticket they had sent and rush with 2 suitcases packed with parts and tools (even a few speakers) for an on the spot repair.

So besides the job I got an extra couple weeks vacation, not bad.

What music did they play there?

Here's a free sample:
http://youtu.be/PhZIYxMr8QY

But ... but .... that's *Brazilian* music !!!
Yes, best Brazilian musicians fled their country's military govenment repression and flourished in Argentina ... the exact opposite happened after 1976 
Oh well.

[sdman]

Amp is working fine, the autoformer without a doubt is badddd!!!. The 120vac did a job on it.

sam