I picked up another Univox guitar amp. Its an early 60's Univox U-102. There's very little information on this amp. I was lucky to find a schematic. It has a 12" Jensen speaker that dates to 1965. Runs on a 6AU6, 2 - 12AX7s, a 6CA4 and 2 - 6AQ5s. Its all original with two prong power cord. The Suzuki caps and the remains of a Sansui label on the top of the cabinet give it away as made in Japan.
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Univox U-102 Tube Amp
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Originally posted by DrGonz78 View PostWould love to a picture of the speaker when you get to it.
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Just curious... back in the day when this amp was new, was Jensen selling the Gold Label speaker? (It looks like a Gold Label in the pics above). Take a look at this ad on Reverb.com. The speaker does say Special Design but it looks different - like the P12R square alnicos. https://reverb.com/item/1502030-vint...-great-tremoloIt's not just an amp, it's an adventure!
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Originally posted by TomCarlos View PostJust curious... back in the day when this amp was new, was Jensen selling the Gold Label speaker? (It looks like a Gold Label in the pics above). Take a look at this ad on Reverb.com. The speaker does say Special Design but it looks different - like the P12R square alnicos. https://reverb.com/item/1502030-vint...-great-tremolo
https://reverb.com/item/3379137-univ...inal-reduction
This is another U-102 listing with what appears to be a gold label Jensen.
https://www.worthpoint.com/worthoped...ombo-140690892
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Originally posted by TomCarlos View PostDid you have a third link in your post? I do not see a link to the schematic. Can you please post that for us. Yes, this is a hard one to find!!
I downloaded the image. Here it is.
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I finished recapping the U-102. I also replaced the rectifier tube socket and put on a grounded power cord. The volume is good. It actually sounds pretty good but something is a little off. I don't get a full spectrum of tone adjustment when I turn the tone knob. A small turn of the knob from all bass goes to all treble. Then 3/4 of the rest of the turning is all treble. Also getting breakup on the low notes all the time. I was short a cap when I replaced the 6AQ5 cathode bypass cap. The schematic calls for a 20/25. It had a 25/25. All I had on hand was a 47/50. Is that where my problem lies?
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That 12AX7 Gain Stage/Phase Splitter is interesting.
The first 12AX7 triode is a gain stage with a bootstrapped anode load resistor.
The second 12AX7 triode is a Paraphase (Seesaw) Phase splitter.
Cathode signal is fedback (as positive feedback) to input stage to bootstrap the anode load.
Note the 50K anode load of Paraphase Splitter anode and the 100K cathode load resistor which is effectively in parallel with the 100K bootstrap resistor (the one from the top of the anode load to B+ node), so 50K load at cathode too.
I have not seen this before.
Cheers,
Ian
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It looks like a Jeffery circuit arrangement:
https://www.americanradiohistory.com...ld-1947-08.pdf
https://www.guitargear.net.au/discus...?topic=51615.0
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