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  • Univox U-102 Tube Amp

    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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  • #2
    That is a beautiful amp! Looks to be very well made and it's in great condition. Thanks for sharing some pics. Would love to a picture of the speaker when you get to it. Score!!
    When the going gets weird... The weird turn pro!

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    • #3
      Originally posted by DrGonz78 View Post
      Would love to a picture of the speaker when you get to it.
      Thanks! With little to go on I figured I'd take a chance. I plan on replacing the electrolytics and oil filled caps. Here are pics of the speaker. Someone wrote 16ohms on the basket, but it measures 5.7.
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      • #4
        Maybe at some point someone reconed it with an 8 ohm kit?
        "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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        • #5
          Originally posted by g1 View Post
          Maybe at some point someone reconed it with an 8 ohm kit?
          I just wrote it off as someone mistakenly labeling as 16ohms. But now you have me thinking. So I pulled the speaker. Here are pics of the cone.

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          • #6
            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-tremolo

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            • #7
              Originally posted by TomCarlos View Post
              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-tremolo
              I love the mysteries that come with these old amps. The markings on the speaker indicate 1965 production date. Unless its 1975. Here's a link to another U-102 with a blue label Jensen. This is the listing where I scored the schematic. Otherwise the schematic was nowhere to be found.
              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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              • #8
                Did 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!!

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                • #9
                  Originally posted by TomCarlos View Post
                  Did 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!!
                  It was in the first link. The amp posting has pictures of the amp and one of pic is of the original schematic.

                  I downloaded the image. Here it is.

                  Click image for larger version

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                  • #10
                    Here it is in pdf format: UnivoxU102.pdf

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                    • #11
                      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?Click image for larger version

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                      • #12
                        These are the voltages I measured:
                        First filter cap - 331.7V
                        Second filter cap - 294.8
                        Third filter cap - 247.5
                        6AQ5 plate - 325.6
                        6AU6 plate - 154.2
                        1st 12AX7 plate- 206.6
                        2nd 12AX7 plate - 286.9

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                        • #13
                          I take back everything I said. The amp sounds incredible!

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                          • #14
                            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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                            • #15
                              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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