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Post subject: 94 Twin Amp dead after new tubes
Posted: Sun Jan 26, 2014 1:47 pm
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So I have a 94 Twin Amp project I've been working on. Here's the story. I picked this up cheap used from a Guitar Center. It had a major mishap with UPS on the way to me and the cabinet was somewhat wrecked, but the amp worked. I got GC to refund me a good chunk of change and repaired the cabinet myself, got it even cheaper. The amp had definitely been used pretty hard. After getting it back together, I have noticed some sound issues. At a rehearsal after about an hour, it suddenly got really broken up sounding with no balls whatsoever, real buzzy sounding. I figured it might just be the tubes, the power tubes were not matching, and when you turn the mix knob up to use the effects loop there was clearly microphonic feedback. So I replaced all the tubes and biased and balanced according to the manual. It sounded so much better! So today I decided to give it a test by using it at church today, that would give it 5 hours of power on. It sounded great at the beginning of rehearsal, then I thought it was my imagination and it might have been getting buzzyish. It sat in standby until the first service. Total time on so far about 1 hour. So I go up for the first service and switch it off standby, and it took much longer to get sound for some reason. But it was working. Then literally 10 seconds into the first song....pppttthhhh, no sound. Jewel light still on but no sound. Switch channel, no sound. So I turn it off and then back on. It comes back to sound for about another 10 seconds and the nothing again no matter what I tried.

So I'm looking for a couple of things. A) any idea what your guess is to what happened. And B) does anyone know of any good amp techs in the Bangor, ME area? I have one I have used before and am going to call tomorrow, but he's pretty old so I'm not sure if he's still in business. Thanks.

Dave


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Sun Jan 26, 2014 2:42 pm
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Is it a printed circuit or point to point ?

IMO it is a printed circuit and one or some copper connexions are broken or solder are broken .

That is why it work some time .

If you know how to solder and know how to remove amp chassis and look at the circuit you can look at it and fix it ( ? ) .


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Sun Jan 26, 2014 2:49 pm
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Is this the amp you are talking about?

http://ampwares.com/amplifiers/fender-t ... -the-twin/

Without knowing more or seeing the amp, and assuming you biased and balanced the power tubes properly, my guess would be that the power supply took a dump, particularly the main filter caps.

http://ampwares.com/schematics/the_twin.pdf

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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Sun Jan 26, 2014 2:52 pm
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It is the 94 Twin Amp which is the model after the red knob twin. Thanks for the advice. If anyone knows any Maine techs it would be super helpful. Thanks again.


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Mon Jan 27, 2014 1:48 am
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Dmerch1969 wrote:
It is the 94 Twin Amp which is the model after the red knob twin. .



This do not help ;

Look here , photos .

http://ampwares.com/?brand=fender&line=twin


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Mon Jan 27, 2014 5:50 am
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According to that Ampwares site it is the "Evil Twin". However, the site information for that amp is not correct. The picture is the 94 Twin Amp, but the schematic shown on that site is for what they called the Pro Tube Twin Amp which I think took over for the 94 Twin Amp in 2000 or 2001. That model added the tremolo feature and adjustable effects loop levels, it is a very different sounding amp from the one I have. The schematic for my amp actually says "94 Twin" on it. It has the mix presence and reverb knobs and a switchable effects loop level. I already have the schematic for it. I was just posting for any possible diagnoses from describing the symptoms my amp was experiencing. Thanks for the links though.

D


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Mon Jan 27, 2014 6:07 am
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Dmerch1969 wrote:
I was just posting for any possible diagnoses from describing the symptoms my amp was experiencing. Thanks for the links though.

D


I have this 94 Twin schematic and owner manual on my archives . It is a printed circuit and you need some skill and know how in electronics to work on .

Possible diagnose ! Read my post January 26

To see if any printed copper circuit or solder are broken , you need to remove the main printed circuit , hard job . :(


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Wed Mar 05, 2014 6:48 pm
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So an update and another question. It turns out that my problem was a lead coming off the second tube in from the right side (looking from bottom) wasn't even soldered. The wire above it on the same post was soldered, but it appeared that the one underneath was missed. The tech fixed that and checked out all the solder points for $75. Seemed pretty reasonable to me. And since then I haven't had any repeat issues.

The new problem is weird, and I figured that I would once again run the symptoms by you folks to see if you had any thoughts. So on the gain channel running the gain on 3 and the volume on 3 (yeah, a little on the loud side, but in was testing it out), all tone controls on 5. Here's what happens. I play the B string on the 10th fret and the note plays for a second, but the amp seems to pull the note down and want to start feeding back at an octave higher. It sounds almost kind of like what a noise gate would do if the cutoff was set too high, except for the slowly building octave higher feedback. Any ideas?

Not looking forward to a return trip to the amp tech, but I would kind of like things to be behaving normally. Thanks.

Dave


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Post subject: Re: 94 Twin Amp dead after new tubes
Posted: Wed Mar 05, 2014 6:56 pm
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Dmerch1969 wrote:
It sounded great at the beginning of rehearsal, then I thought it was my imagination and it might have been getting buzzyish. It sat in standby until the first service. Total time on so far about 1 hour. So I go up for the first service and switch it off standby, and it took much longer to get sound for some reason. But it was working. Then literally 10 seconds into the first song....pppttthhhh, no sound. Jewel light still on but no sound. Switch channel, no sound. So I turn it off and then back on. It comes back to sound for about another 10 seconds and the nothing again no matter what I tried.

So I'm looking for a couple of things. A) any idea what your guess is to what happened. And B) does anyone know of any good amp techs in the Bangor, ME area? I have one I have used before and am going to call tomorrow, but he's pretty old so I'm not sure if he's still in business. Thanks.

Dave



This sounds like the makings of instability like parasitic oscillations. Could come from anywhere in the amp's circuitry. But, usually in the phase inverter and output stages. Prolly needs a good tech, to sort out the physcially and possible electrical damage to the amp.

Sorry. :(


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