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Post subject: super reverb
Posted: Thu Feb 09, 2012 5:20 pm
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I have only low volume on the vibrato channel on 3 and 10 on volume knob. This is a '73 rebuild to AB763......normal channel is great. I lifted the 2 pot ends of the roach and no change. All pots have been removed and cleaned and the volume pot is new 1M.

I will try sending photobucket pics

http://photobucket.com/superreverb

Pi #1 on V2 is 179v....not 270v. Tremolo works good but low volume and reverb is great.

Any ideas would be appreciated.

Doc


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Post subject: Re: super reverb
Posted: Thu Feb 09, 2012 6:40 pm
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I presume voltage on V1 in around 270VDC? Would indicate a bad 100K-ohm droppping resistor or a shorted V2 12AX7 (7025). Have you tried another 12AX7 in V2?


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Post subject: Re: super reverb
Posted: Thu Feb 09, 2012 7:20 pm
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I'll try that......... again.
Jim


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Post subject: Re: super reverb
Posted: Fri Feb 10, 2012 11:41 am
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:D Found the problem......bad 250pf tone cap for the reverb channel. We now have 270v at pin #1 on V2

Doc


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Post subject: Re: super reverb
Posted: Fri Feb 10, 2012 2:03 pm
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Not quite sure I understand. Was the 250-pico farad cap in the wrong place? There is a 250-pico cap in the tone stack of both the NORMAL & VIBRATO channels?

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: super reverb
Posted: Fri Feb 10, 2012 3:18 pm
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It was the one for the vibrato channel....above V2.


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Post subject: Re: super reverb
Posted: Fri Feb 10, 2012 5:19 pm
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Sorry, mis-read your post. That is the tone stack cap.

Good find. Enjoy the amp!


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Post subject: Re: super reverb
Posted: Fri Feb 10, 2012 5:38 pm
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I wonder why it went bad ?...it was new.

I really do enjoy this amp !


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Post subject: Re: super reverb
Posted: Sun Feb 12, 2012 9:14 pm
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Dunno. Could be a bit too much heat when soldering. I use silver mica 250-pico caps in this part of the amp. Has a bit more bandwidth (better treble response) than ceramic types. Cheap fix-it. I get them here:



http://www.partsconnexion.com/capacitor ... rmica.html


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Post subject: Re: super reverb
Posted: Mon Feb 13, 2012 9:05 am
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Thanks for the tip....I may have gotten it too hot.
Thanks for the parts source....


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Post subject: Re: super reverb
Posted: Tue Feb 14, 2012 4:00 pm
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Try this trick when soldering small caps and resistors. Get a small lightweight alligator clip and clip it to the body of the component before soldering. This helps to dissipate excess heat & prevent damage. I borrowed the idea from techs doing computer work and stomp box tech replacing IC chips.

http://i.ebayimg.com/t/Small-Size-20-pi ... ~~60_3.JPG


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Post subject: Re: super reverb
Posted: Tue Feb 14, 2012 4:53 pm
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Great idea....I'll do it.

Thanks
Doc


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