Salvaged Univox - now what?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by telefmt, Apr 29, 2008.

  1. telefmt

    telefmt Member

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    Hi all - I'm wondering if this is a lost cause - a 1965 Univox 30 watt combo model U305R - had a 15" Jensen in it. It's DOA now - first glance shows no fuse, lead to power cord is disconnected, and somebody snipped some of the wires between the tube sockets and the circuit board. I tried the Univox forum, but not much life over there. The link to the schematic for this amp model doesn't work. On the positive side - apparently all the tubes worked last time the amp was plugged in. It has 3 Mullard 12AX7s (stamped Great Britain), the rest appear to be old RCA tubes - 2 6973 power tubes, 6AN8,6AT6 (in the 6AV6 socket) and a 6CA4. I saw a couple old threads on here and I'm in the same state as wakarusa - but is this just a pile of old parts? I'm not good enough to track this down on my own - I can handle a power cord replacement or installing a speaker jack - but that's the limit of my experience so far. Some pics:

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. Trout

    Trout Member

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    Edit, I just noticed you posted over there? Sorry

    Here is one on youtube
    http://www.youtube.com/watch?v=iUEJWY3ozQI


    It is well worth fixing!

    Univoxes are way underated on resale value.

    There is a lot of info over at http://forums.univox.org/

    In fact, there is a recent thread going on that model http://forums.univox.org/topic.asp?TOPIC_ID=1561


    U-305R -(1, 2, 3) -1965 Japanese tube guitar amp. 15" Jensen Special Design speaker (220512). Tubes are: 1- 6CA4, 5- 12AX7A, 2-6973. 2 channels, both have Bright and Normal inputs with Volume and Tone controls. Channel 1 is HIGH . Channel 2 is LOW. Reverb Depth, and Tremolo with Speed and Intensity controls. Tube driven spring Reverb works on channel 1 only. Power Off/On/Standby switch. Extension speaker jack, Tremolo and Reverb footswitch jacks.
     
  3. capnjuan

    capnjuan Member

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    Hi telefmt: I also have a Univox 305R but in the 'tall boy' configuration; 32" high cabinet w/ original Jensen 15" Special Design speaker. Mine has the same rectifier / preamp / reverb tubes as yours except it uses 7591s not 6973s. My copy works but is waiting its turn on the bench. I also found an original dual Univox footswitch on eBay. I have a copy of the U305R / 6973s schematic if you're interested - PM w/ your email address. The U305R driver/phase inverter and outputs:

    [​IMG]

    I'm not the strongest tech around but I can't say that I've seen anything similar with all the coupling caps; Anybody?

    Anyway, I won't be working on mine for a while but if/when, I can take some pics that will show how the wiring goes; together with the schematic, give you a good shot at rehab if you want to take it. John
     
  4. Trout

    Trout Member

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    Hey, if you get a chance, mail me a copy of that schematic also, I'll put it in my archives, that is a hard one to locate.

    Trout
     
  5. telefmt

    telefmt Member

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  6. capnjuan

    capnjuan Member

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    Hi Trout; email w/ schematic sent. John
     
  7. capnjuan

    capnjuan Member

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  8. Trout

    Trout Member

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    Thanks John!!!

    Excellent copies!
     
  9. capnjuan

    capnjuan Member

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    My pleasure Trout; got any intel on the phase inverter? BTW not used on the better-known U45B; an amp very similar to the last of Gibson Gibsonette series the 8(T) 12AX7, 2X6BM8. John
     
  10. rrobards

    rrobards Member

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    Great discussions guys!! Thanks! I am also in need of schematics for the U305R. CapNJuan, can you email a copy? rrobards@elutions.com It would be greatly appreciated. A buddy of mine just gave me the amp and it never did work when he had it. He played around with fixing it years ago but didn't get far. I googled univox and found all of this information just waiting for me. I couldn't believe it.

    I have copied the detailed discription of rework that was posted in the forum.univox.org page by thomas. Really great work Thomas, thanks!!

    If/when I get this working, I'll be happy to provide any insights that I might stumble upon.

    Ron
     
  11. capnjuan

    capnjuan Member

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    Howdy Gents: I finally got my U305R on the bench, old can cap left, new one on right

    [​IMG]


    Changed selenium bias rectifier to silicon

    [​IMG]


    Changed power cord and switch, snipped out the death caps:

    [​IMG]


    Struggling with footswitch; no twin, 1/4" cables in the same jacket in the aftermarket:

    [​IMG]


    A later, cleaner version of this chassis came/went on eBay recently. This is an older model with oil caps where the newer one had mylar/polyester:

    [​IMG]


    The original 15" speaker is in pretty good condition; no problems with cone. Frame got a coat of Metal Ready; something to slow/stop the rust in a few spots:

    [​IMG]


    Finally, as a bonus ...... the amp might have been owned by a famous musician ... named.....

    [​IMG]


    Somewhere along the line, someone etched the name 'Petty' on the chassis backpanel ... HEY TOM ... Factoid; the amp was new about the time Tom Petty was 17/18; he grew up in N. Florida, I bought the amp in FL ... ya never know about these things. I have NOS 6AN8 and 6AV6 reverb drive/recovery tubes and a matched pair of NOS Tung-Sol 7591s. It's a fixed-bias amp with a 10 ohm cathode resistor but no means of adjustment.

    Left to do: the trem and bias caps, one of the reverb pots, and while it's out, I'm going to try to do something about the reverb cables being hard-wired at the chassis; makes getting the chassis out and in a pain considering the reverb can has to be tugged out and stuffed in its bag with a third hand. John
     
  12. AL30

    AL30 Member

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    :eek: If someone doesn't mind I would like a copy of that schematic as well. I have an old Lafayette that isn't working and I need to take a look at it but can't find a schematic for it. This sounds similar. And thanks for the pics.

    Thanks

    atlarry <at> yahoo <dot> com


    AL
     
  13. capnjuan

    capnjuan Member

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    Email w/ schematic sent. J
     
  14. capnjuan

    capnjuan Member

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    Over on the Ampage BB, a poster had an amp branded 'Meteor'; 2 X 12AX7, 2 X 6BM8, 12" speaker. Closer inspection showed it was a part-by-part dupe of the Univox 'stairway to heaven' U45B probably made under license from Univox. J
     
  15. capnjuan

    capnjuan Member

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    Bump: When the amp was test-fired, it blew one of the caps in the PI. These are 40 year-old oil-filled caps ... and there's no way of knowing how stable the rest of them are so, except for two of them on the far left, they've all be switched out for Mallory 150s or fresh electrolytics:
    [​IMG]

    Hard-wired reverb out/in connections replaced with rca jacks and oil-filled trem cap replaced with Orange Drop. J
     
  16. epluribus

    epluribus Member

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    Wow, a U305...not your everyday snag. Glad to hear you found out what it is. I wouldn't mind a copy of the schematics either, just on the event I either acquire one or build one. Great amps for sure.
     
  17. HeeBGB

    HeeBGB Member

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    I have owned one of these for the past 10 years or so. Great little amp. Mine has been converted from 6973's to el84's. I could use that schem too! I'll post some pics when I get the chance.
     
  18. capnjuan

    capnjuan Member

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    Happy to share U305R / 6973 schematic; PM me including return email address. J
     
  19. slider313

    slider313 Silver Supporting Member

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    Those grey oil filled caps are know to leak. That's the first thing to replace after the electrolytics. Cool amps with a nice crunch.
     
  20. capnjuan

    capnjuan Member

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    If you go back to telefmt's first pic in this thread, slide full right and then count back 5 caps to the left ... that's exactly what happened in mine after I changed out the can cap ... phhttttt ... followed by a little plume of white smoke. There might be any number of reasons to tug the chassis out later but this isn't going to be one of them. PITA but ... J
     

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