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68 Fender Showman innards..all look normal?

Discussion in 'Amp Central Station' started by Denton, Mar 3, 2021.

  1. Denton

    Denton Tele-Meister

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    Considering this for a bass and guitar double duty head. For those with the knowledge, does anything look out of the ordinary? I have pics of a 67 I used to have and I see a couple differences between the two:

    335DA227-BAE9-444D-9ACB-D276AEF18BB2.jpeg EB9333E8-9B70-4FBC-9875-554B9AB99F79.jpeg D8CE7835-B3E6-4D5D-B919-2500D5773510.jpeg
    B81B074E-74D6-4502-9EE8-38252A876CA8.jpeg

    I know the blue signal caps are what I want and the caps in the doghouse have been changed. On that last pic...what is the big long block by the transformer and big mustard colored cap? Where’s the bias pot?

    Obviously I’m not a tech...but I want to be one someday! Hoping for some experts to chime in.
     
  2. SoK66

    SoK66 Tele-Afflicted

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    There's some weirdness going on with that big brown cap by the power tubes, and that ballast resistor between the two PT grounds. Looks like the PT gor pretty hot at one time. Not sure why a tech would replace the filters and the vibrato bypass capacitor, which look fine, but not change the bias cap. Thos black dual bypass caps on the repamp were pretty good componenets but doubtful they'd still be in spec. If it were mine (I campaigned one of thos for a few years back in the '60s, which is why I have hearing aids now) I'd have a good tech check all that out. The ballast resistor has me stumped, but were I to guess I bet someone was trying to reduce the B+ / plate voltage. Best wa to do that is reduce the line voltage with a "Brown Box", Tone Perserver, etc. buck transformer outside the amp.
     
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  3. Denton

    Denton Tele-Meister

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    Should I walk away and look for another one in your opinion? I haven’t purchased it yet. I want to avoid an amp tech visit of at all possible.
     
  4. Engine Swap

    Engine Swap Tele-Afflicted

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    Looks mostly original, aside from the resistor and cap that were mentioned. Filter caps have been replaced. The black gunk on the bottom of the PT is not uncommon - my 1966 Showman has it.

    Good bones, but keep in mind that it's 53 yo at this point. You will need to replace the remaining electrolytics in the bias circuit and cathode bypass. Any decent tech can reverse the resistor and cap mod that's in there - easy job.

    Boils down to price - if you can get an untouched one or one that has been updated for the same price, then consider going that direction.
     
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  5. Denton

    Denton Tele-Meister

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    Thanks for the replies. I have a verbal offer but haven’t sent the funds, which I hate to go back on unless there’s some serious red flags. The gunk on the T was something I forgot to ask about as well...thanks for catching that.

    As long as the mods are a minor fix, then I will proceed. I just don’t want to end up with a hobbled together basket case. I went through that recently with a Bassman via a CL trade that I had to drop some $$$ in.

    I have heard a video of it and it sounded good. Price is 15-20% below Reverb prices.
     
  6. Wally

    Wally Telefied Ad Free Member

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    ...duplicate post...
     
  7. Wally

    Wally Telefied Ad Free Member

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    That large sandcast resistor and the 150vdc capacitor are odd. It appears from here that they are attached to the pin 8 cathodes. This amp should be an AB763 circuit since it is so early in 1968. However, unless I am mistaken, that capacitor has a date code of the 4th week of 1968. Could it and the resistor are original making this some early experiment that led to the Mixed biased circuits that were introduced with the first true CBS circuits in May, 1968? All of those cathodes should go to ground in the AB763 circuits....but they are all attached in a circuit with that whitish wiring. ???? It would be interesting to see that circuit in person.
     
  8. Denton

    Denton Tele-Meister

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    Wally, what do you think? Pass or purchase based on what you see?
     
  9. schmee

    schmee Doctor of Teleocity

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    Well, how much $ do they want for it?
    Are you capable of returning the bias pot etc to original layout?
    Does the faceplate say Showman or Dual Showman?
    Other than the weird resistor and lack of bias pot, it appears very clean and original inside.
     
    Last edited: Mar 3, 2021
  10. Denton

    Denton Tele-Meister

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    $700. It’s a showman with the 8ohm OT. I’m going to use it with a JBL k140 loaded 60’s Guild 1x15 cab. I made sure it was the 8 ohm as I know some came with the 4 ohm DS OT’s.

    I might be able to do the work myself if I had to, but I just don’t have the experience I feel is necessary to start soldering in there. I’d take it to a tech.
     
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  11. schmee

    schmee Doctor of Teleocity

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    Well, I dont think $700 is bad at all . Is the cab/faceplate clean? I'd pay that if I wanted one. I don't think they go real high on the market. I assume it's a short lived AC568 layout. But maybe it;'s the AA768. The work needed appears simple really, and the filters are already done.

    It's strange, I can't see where the wire that normally goes to the bias pot goes on your layout. It's the wire soldered between the two 220k resistors that make a V shape on the transformer end of the board between the two .1 caps. where does it go?
     
    Last edited: Mar 3, 2021
  12. Wally

    Wally Telefied Ad Free Member

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    I believe this was built before the 1968 circuits were drawn up. I think this because of that chassis stamp date code....8th week of 1968, and there is a true bias voltage adjustment circuit there that looks original rather than the balancing circuit. Both the bias balancing circuit and the fixed/cathode bias circuit were 8ntroduced in May, 1968 schematic.
    I think there is a very good chance that that large resistor and that electrolytic cap are original. I think this because of the date code on that cap....4th week of 1968. As I noted, this amp may have been a factory experiment. Or...could it have been someone’s very quick aftermarket adaptation to the newest Fender circuit???? That mixed Biasing circuit was short lived.....the 1969 schematics went back to a straight fixed Biasing circuit. Fro: here, the wire looks to be period no factory correct. Again, it would be 8nterestingnto see it in person. Oddities from the factory do exist.
    What is it worth?? Well, it has been recapped. The screen grid stopper resistors have been replaced. If you like the sonics, it may be worth that to you. Where else are you going to get a quality 100 watt, handwired amp for $700? I like to make these two channel Fenders have more versatility. There is one sitting in a Dallas studio now that I made the Normal channel into a very different channel...hot and middy. The Deep switch is now a midrange boost. Very nice amp, imho....and the buyer’s opinion as well. I would not advise a JBL in any amp, but that is a subjective opinion. Ommv.
     
  13. Denton

    Denton Tele-Meister

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    Thanks Wally. I should mention this is primarily for bass use. P bass and flats, JBL. I have a 1983 g12-65 loaded Marshall 2x12 cab that I can use for guitar use.

    So this has the original bias set up as opposed to the balanced setup. Cool. I don’t see a pot for that...am I missing something? Excuse my ignorance..

    Ok. I think I’m going to pull the trigger!
     
    Last edited: Mar 3, 2021
  14. Wally

    Wally Telefied Ad Free Member

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    Hey, I missed something as well, Denton! The bias adjustment pot is missing. In two pics we can see a hole where that pot would have been. I had focussed on the 2 x 220K resistors that are in place on the board....but the pot is gone. Check the first picture...upper mid-right near the T I; that chassis stamp? That is where the bias adjustment should be. So....this amp needs a tech assessment and probably a rebuilding of the original bias circuit. Don’t give that $700 for it....
     
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  15. Denton

    Denton Tele-Meister

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    Well glad you caught that for me. I was waiting for the seller to confirm the second channel/vibrato worked before sending the money. Whew!

    Guess I will keep searching for a Showman.
     
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  16. Wally

    Wally Telefied Ad Free Member

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    I am glad I woke up in time, Denton!
     
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  17. Wally

    Wally Telefied Ad Free Member

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    Fwiw, I got some bit more than that for a 1964 Dual Showman that was a perfect fit for the Pro Sonic cab I put it in with 2 x EVI Force 10s. Big time amp.
     
  18. schmee

    schmee Doctor of Teleocity

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    Price guide actual sales.
    Date Condition Sold Price
    2/2/2021 Very Good $800
    1/7/2021 Very Good $750
    12/5/2020 Good $900
    12/2/2020 Very Good $700
    6/6/2020 Very Good $750
    6/2/2020 Very Good $550
    2/17/2020 Good $535
    1/14/2020 Excellent $750
    11/8/2019 Good $620
    10/9/2019 Very Good $675
     
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  19. Denton

    Denton Tele-Meister

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    Thanks for the price guide. I haven’t checked Reverb for that and I should have. Oddly enough, I sold a nice 67 silverface Showman for $635 3 years ago on Reverb. Exactly what I want to get back now. I’ll keep up the search with a focus on originality. I don’t have a tube bass amp for the first time in like 15 years right now as I’ve been selling more stuff and focusing on guitar. But now with things starting to get somewhat back to normal and opening up, I need to get ready for some bass playing
     
  20. sllsll

    sllsll TDPRI Member

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    If you get it definitely replace the bias electrolytic capacitor. Then blackface the output stage and that should eliminate all of the weirdness. The blue molded capacitors indicate that the amp can most likely be made to sound very good.
     
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