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Post subject: Twin Reverb - no sound - could use an opinion
Posted: Tue Feb 19, 2013 6:06 pm
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Hi everybody!

I have a mid 70's Twin Reverb Silverface with JBL's. I bought it new and it has been my primary amp since it left the showroom floor.

A while back, it started blowing fuses. I figured it was about due for some service anyway, so I took it to a well-known, local amp guy here in town. New tubes, caps, general service - it was working when it left the shop. Now, I turn it on, tubes glow and everything powers up, but no audio. Not even hum. Just like the speakers are unplugged, but they aren't.

I could just take it back to the shop I guess, but it was a bit of an ordeal and I'm not looking forward to opening that can of worms again. Before I plunk down another wad of cash somewhere else, any ideas where I could look?

Thanks in advance for all your help!


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Tue Feb 19, 2013 8:54 pm
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Could be bad tubes, bad output transformer, bad solder joint, any number of things.

If the amp tech provided any sort of warranty, you should return the amp to him immediately. Even if he didn't provide a warranty you should go back to him for an explanation.

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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 20, 2013 5:40 am
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But that's where the problem lies. It sat in his shop for weeks before he even looked at it, I had to pressure him to get the amp back. I was glad just to get it out of there.

It's not that he didn't offer a warranty, I'm just hesitant to go there.


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 20, 2013 5:58 am
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You have three options in my opinion

Take it back and deal with the obviously bad tech

Find a new tech

Start studying trouble shooting here and online, I highly recommend some of the Gerald Weber books for the ease of understanding and the plain english he uses to explain.

I would start by at least calling the guy to see what he had done to it to make it work at all and start from there.

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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 20, 2013 12:47 pm
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Thanks! I have a complete list of everything he replaced, plus he gave me back the parts he took out. He told me that the overall problem - what caused it to blow fuses - was a loose tube socket. Everything else was past due maintenance stuff.

He's a nice guy and a good tech - don't get me wrong - but he overextends himself and drives his customers crazy.


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 20, 2013 3:13 pm
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both channels I assume are "quiet"??

Gotta think its was a bad solder joint somehwere that came loose. If you are comfortable. Unplug the amp and pull the chassis and take a look around for something obvious. Like where the wires are soldered to the speaker output jack, etc. Use a wooden stick to poke a round a little.
If you are not comfortable with that then you have to bring it back or at least call the guy.


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Tue Feb 26, 2013 5:26 pm
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I'm making an assumption that you have tried all the input jacks and tried a different cable and guitar?

And please don't put you ear near the speakers. Leo did that once. Just once! :shock:

Art


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Tue Feb 26, 2013 6:45 pm
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PDMan, Do you have a way or a tool to measure the idle bias of those 6L6GCs? If you are getting good readings (30-40mA per tube) --- it's prolly something with the secondary winding connections of the output tranny. The secondary side must be grounded, at one point.

He may have knocked the wires or bent the speaker jacks --- causing no continuity.

If the tubes show no bias, at all --- you have much bigger issues.

One last thing ---- are ALL 12AT7 and 12AX7 good? Do you have some you can sub into sockets, just to rule out a bad pre-amp, gain stage, phase inverter tube?

Good luck!


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Tue Feb 26, 2013 8:25 pm
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Maybe you can tell us what was done to the amp, PD. BTW, which tube socket was causing the problem? I'm with Beemer, on this, but leaning towards a problem with the phase inverter tube or it's circuit. Art

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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 27, 2013 4:59 am
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Check to be sure all tube are seat properly.

Speaker jack / plug are not defective ? Try another speaker.

Did you move amp before it did not work ? Drop it ?


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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 27, 2013 9:35 am
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That reminds me of an huge Ampeg I sold a guy, it left here sounding excellent, i replaced some tubes (very expensive) and had it tweaked and sounding fabulous !
He sends me a text telling me how this is wrong and thats wrong etc......

When he left he had put the amp standing up in the back seat and then through Chicago traffic all the way home.
It was two days before he finally admitted the amp tumbled off the seat on the way home.

Dude had me furious and wondering what in the world had gone wrong.

100lbs on Ampeg slamming to the floor isn't a good thing !

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Visual Sound Route 66
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Post subject: Re: Twin Reverb - no sound - could use an opinion
Posted: Wed Feb 27, 2013 2:47 pm
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blues bondsman wrote:
That reminds me of an huge Ampeg I sold a guy, it left here sounding excellent, i replaced some tubes (very expensive) and had it tweaked and sounding fabulous !
He sends me a text telling me how this is wrong and thats wrong etc......

When he left he had put the amp standing up in the back seat and then through Chicago traffic all the way home.
It was two days before he finally admitted the amp tumbled off the seat on the way home.

Dude had me furious and wondering what in the world had gone wrong.

100lbs on Ampeg slamming to the floor isn't a good thing !



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