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Old 2nd September 2013, 02:45 PM   #1
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Default Ampeg VT-22 dead OT?

Hi all, I am now working on a very nice and old AMPEG VT-22 guitar amp I've found in a recycling place. It is in very good physical condition, original Eminence speakers and I think most of the original Magnavox tubes. Only one 7027A (output tubes) was missing. I've replaced it with a 6L6GT to "make it work". I've opened the amp, cleaned everything (not much to do as it was in very neat condition) de-oxed pots & switches, etc. I then powered it up using a variac. Went up slowly and everything seems perfect except: no sound at all... not even a shhhh or a plop, nada!

Started probing with a generator and oscilloscope and got all the way to the plates outputs where I hooked my scope and I see my tone getting there very nice and high. Nothing after that. Looks like my output transfo is out...

I "probed" it with an ohmmeter and at the primary I get around 140 ohms on the total winding (between violet and brown), like 65 between the violet and orange and the rest, 75 ohms betweek the brown and orange. According to what I've red already this seems to be OK. I also disconnected the transfo from the cct to be sure and I got these readings again. I then looked at the secondary where I've red 1.8 ohms total (white & brown) and around the same for the others (yellow and red). Are these last readings normal? Would my transfo be "shorted"? As I can see my amplified signal at the primary winding and not at the secondary this really looks like the OT is dead... Is it? Am I missing something here?

Thanks for any advice! If anyome knows where I could get one of these OT not too expensive I'ld be really happy! I found some "compatible" around CAN $165...

I also do not want to put $200 for a tranny and get to the same point... Any particular way I could verify if this transfo is dead?
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Old 2nd September 2013, 03:41 PM   #2
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If you have resistance of 1.5R on the 8R tapping, that is about right. Check a speaker wired directly to the transformer tap.
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Old 2nd September 2013, 06:06 PM   #3
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Well I did... Nada... All there is after the taps is a switch for 2, 4 & 8 ohms. I've tried all directly. No sound...

I now am thinking about why somebody would put such a good & nice amp for recycling...
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Old 2nd September 2013, 06:26 PM   #4
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THANK YOU SO MUCH !!!!!

I went to measure my speakers: both open !!! Hooked a little Radio-Shack box and BOOM!!!

Sounds pretty nice!

Now: Should I get these repaired or should I replace them? I've heard they are not very good...
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Old 2nd September 2013, 06:34 PM   #5
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If they're not very good, keep looking for speakers that would best suit the use that you are going to use them for.
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Old 9th September 2013, 05:35 AM   #6
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Well at least that's an easy fix.
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