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1980/81 Pro Reverb Ultralinear

Discussion in 'Amp Tech Center' started by scorchy, Oct 17, 2016.

  1. scorchy

    scorchy TDPRI Member

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    Sort of a funny story. I found a 1981 Super Reverb on Craigslist for around 350. Ad said that it had a slight hum and would need to be checked out - sold as is. I totally understood what I was getting into. I have some experience with electronics and feel pretty confident with recapping, replacing, and full-on revamping. I played through the amp - all seemed well. I take it home and within a few days, the vibrato channel goes out - super low volume. So, I open up the amp and discover that it's not a Super Reverb at all. It's a Pro Reverb (stamp on the side) Ultralinear.

    I'm now researching for a layout that will allow me to find out which caps I'll need, as well as other items that may or may not need to be replaced. If anyone happens to know of where to obtain the layout for this amp, it would be greatly appreciated. I thought it was the AA165 version, although this amp has a mid knob on both channels along with a push/pull master volume.
     
  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Take a look at this schematic and try to verify it fits your amp. The little box at bottom center says Pro Reverb and it has an ultralinear output transformer that's been modded to non-ultalinear:

    [​IMG]
     
  3. Ringo

    Ringo Poster Extraordinaire

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    So it was a Pro Reverb chassis in a Super Cabinet? I know when Fender went to the UL series of amps they used the same size chassis for everything, Twin, Super, and I guess Pro Reverb too, different trannys and the Super and I guess Pro have a pair of 6L6s, ss rectifier, Twin has a quad w SS rectifier.
    Still should be a good sounding amp when you get it sorted out, I had a UL Super Reverb, 70s watts, and it sounded good, great clean tones and reverb / tremolo.
     
    Wally likes this.
  4. scorchy

    scorchy TDPRI Member

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    Thanks @robrob. I'll check it out and see if it matches up. @Ringo, from the layout of the board and filter caps, it definitely looks like a pro. I'll get some pics up soon.
     
  5. Ten Over

    Ten Over Tele-Holic

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    I think that the Bandmaster Reverb, Pro Reverb, and Super Reverb all have the same circuit in the same chassis. The only difference is the faceplate and nameplate and a two or four speaker cabinet. So you really do have a Super Reverb if you have four speakers and the proper plates.
     
  6. Ten Over

    Ten Over Tele-Holic

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    Why would you give him a schematic with a mod? This schematic without any mod's is what he probably has.

    Bizarre mod, by the way. The 470/5W will burn up on the first power cord if you can hit it before the 2K/10W WW burns up just sitting there with 500V on it. Why would anybody want these resistors, anyways?
     
  7. Lynxtrap

    Lynxtrap Tele-Holic

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  8. scorchy

    scorchy TDPRI Member

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    Thanks, everyone. I'm going to go through the amp and do a full recapping. There's also a broken lead on one of the power tube sockets - I'll just do a full replace. Should be a fun project. The quad of caps and diodes in the schematic (coming off the red leads) seems to be the filter caps, which I'll replace as well.
     
  9. Wally

    Wally Telefied Ad Free Member

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    Scorcher, since you mention that you'll "replace those as well" in reference to those caps around the rectifier, one wonders what you mean by a "full recapping"? Those 220mfds in series constitute the first stage of filtering and would be a natural part of a recap. The two 70 mids are the bias cap electrolytics. The 20mfds/500V electrolytics are the remaining filters. There are some electrolytics in the circuits functioning as bypass caps.
    What else constitutes this full recap? Just curious...
     
  10. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

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    BTW...I gigged one of those for years...back in the 80s when we played LOUD, I got some pretty good sounds from it.
    When things got quieter, I daisy-chained it (or ABY'd) it with a tweed Deluxe 5E3 and got some really lovely tones.
     
  11. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Because it's the only Ultralinear Pro Reverb schematic or layout I could find.
     
  12. Wally

    Wally Telefied Ad Free Member

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    Ten Over if you would be so kind as to explain 1) why this modded schematic will not work and 2) how you would propose to change such a circuit from ultralinear to non-UL operation?..for the benefit of those of us who don't fully understand why you say the mod will not work? Also, I am supposing that you intended to type "power chord" instead of "power cord", correct?
    I am not trying to hijack this thread. Since the OP is getting into amp work, any education concerning the circuit is of interest, IMHO.
     
  13. scorchy

    scorchy TDPRI Member

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    The Vibrato channel has a 90% volume loss. Also, the reverb and vibrato (tremolo) aren't functioning anymore. I've checked the tubes and did a chopstick tap. The only other thing I can think of is to just recap it or replace the boards altogether.
     
  14. xafinity

    xafinity Friend of Leo's

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    "Bizarre mod, by the way. The 470/5W will burn up on the first power cord if you can hit it before the 2K/10W WW burns up just sitting there with 500V on it."
    Would it still burn up if the first power cord is a 3 conductor? :D
     
  15. scorchy

    scorchy TDPRI Member

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    It's the bias supply board that may prove problematic. This isn't mine, although it's pretty exact.

    [​IMG]
     
  16. Ten Over

    Ten Over Tele-Holic

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    1) It probably will work up until one or the other of those resistors burn up or you hit the power cord with a chainsaw. That 2K/10W WW will drop 250mA to ground at 500V. That is about the entire rated output of the PT. I remember those things when they first came out and I noticed that the PT's ran much hotter than previous models. Putting an additional 250mA load on them just might cause catastrophic failure.

    The 470/5W resistor would probably have 72mA or so across it at idle for about 2.4W, so the 5W rating at double the actual watts is right in there. But, after repairing the power cord, driving the power tubes very much beyond idle will overload that resistor.

    2) I never really said that the mod will not work. I just said that it will burn up. I've used UL OT's as non-UL OT's before and I just cut the UL taps, inserted a choke into the HV rail, and wired it as usual. I'll bet money that this amp will work if wired like that.


    At 23,000+ posts, I am pretty sure that you know what I meant by "power cord". One of the striking things about this forum is the widespread use of erroneous words. However, you just about never see anybody comment on it, so I thought that it would be a violation of forum ettiquette to do so.
     
  17. Ten Over

    Ten Over Tele-Holic

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    Heh, heh, heh. I'm pretty sure auto-correct did that to me.
     
  18. Lynxtrap

    Lynxtrap Tele-Holic

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    I don't think you need to change those particular caps, and they wouldn't be causing the problems you describe.
    You should maybe start by checking voltages at all relevant points throughout the whole amp.
     
  19. Lynxtrap

    Lynxtrap Tele-Holic

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    3 conductor doesn't matter. The amp won't work after you hit the cord with a chainsaw. :D

    On the serious side, I don't see why those resistors would be added either.
     
  20. overlock

    overlock Tele-Afflicted

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    That board has your HT supply as well as bias, if it corresponds to the schematic. Four diodes arranged as a bridge rectifier, with little snubbing capacitors to reduce switching noise. Shouldn't think you'll need to replace those, but I'll defer to wiser heads.
     
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