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Post subject: 1973 Twin Reverb blowing fuses
Posted: Fri Dec 03, 2010 11:22 am
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This amp has been dropped .....chassis is bent in 1/2 inch behind master volume and the Power Transformer pushed/bent the chassis 1/2 inch in, toward the top of cab. There were 2 loose solder joints on the brass frame behind the pots. I have replaced the main filter caps.

With all tubes out it still blows the fuse...immediately.

With the 5 wires clipped ( see pic ).....3 to bias board and 2 to ground, it does NOT blow the fuse and the pilot light stays on.

The voltages to the bias board are 240, 240, and 40 ...is this CORRECT ?

I have repaired about 15 to 20 tube amps so I am a newbie, but the "bug" has bit me and I love it.

Doc


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Posted: Fri Dec 03, 2010 11:30 am
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I'm not seeing a pic, Doc.

Arjay

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Post subject:
Posted: Fri Dec 03, 2010 1:12 pm
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[img]http://flick.kr/p/8Y64yn
[img]http://flick.kr/p/8Y96U7
[img]http://flick.kr/p/8Y64yn

hope these pics work

Doc[/img]


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Posted: Fri Dec 03, 2010 1:39 pm
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is there an easy way to add photos ??? I have been trying for an hour or two.

I did the Flickr thing and the copy/past does not work.

I used to think I was pretty good at transferring photos...Ebay, Craigs List, etc..

Any tips appreciated.

Doc


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Posted: Fri Dec 03, 2010 1:56 pm
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Image


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Post subject: pics ?
Posted: Fri Dec 03, 2010 3:34 pm
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Posted: Fri Dec 03, 2010 3:35 pm
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Still no joy, Doc.

I think Photobucket may be more "user-friendly".

Arjay

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Posted: Fri Dec 03, 2010 3:49 pm
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Hi Arjay.

I just sent some pics to your email address..hope that is OK ?

Doc.......................I'll try using my Youtube account for more pics.


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Posted: Fri Dec 03, 2010 4:00 pm
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They haven't shown up yet Doc, but check out this thread......

http://www.fender.com/community/forums/ ... ht=#567293

You'll see my tutorial for using Photobucket about 2/3 of the way down the page.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Fri Dec 03, 2010 4:48 pm
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Check those diodes for damage. Bias Supply voltge should be (-50-53 VDC). Must be minus VDC at point off BIAS POWER Supply diode. See schemo:


http://www.ampwares.com/schematics/twin ... _ab763.pdf


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Post subject:
Posted: Fri Dec 03, 2010 6:46 pm
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Hi Doc, I've seen a few amps like this but the deflection was more like 1/4". The 2 grounds(center taps)off the power trans need to be securely grounded to the chassis, inorder to get an accurate ACvoltage reading from the other 3 leads. Then I'd do a continuity test on all the other grounds, with an eye towards the pots located near the chassis deflection. You may have to install a ground buss wire for the pots. The pots and pot tabs will also need to be checked and tested. They may be history, if they took the full brunt of the drop. But yeah, check those diodes, like BMW suggested. My guess would be a live connection on one of those pots are touching the chassis. Good Luck ! Art

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Posted: Wed Dec 08, 2010 10:07 am
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update on the 73 Twin Reverb .....she LIVES !!!

The bias components went "south"

All new diodes and 2 100v caps. For my $250 garage "FIND" this Twin is back from the dead.

Thanks for everyone's your help,...From all of us here in " Newbie Town. "

Doc


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Post subject:
Posted: Wed Dec 08, 2010 7:28 pm
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Excellent, glad my guess was wrong ! Good Luck ! Art

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