My Frankenstein Deluxe reverb is acting up.

Discussion in 'Amp Central Station' started by The Grim Peeper, Jan 22, 2020.

  1. The Grim Peeper

    The Grim Peeper Tele-Holic

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    My Deluxe Hybrid is acting up. It is a 1965 deluxe with a bandmaster power tranny in it and a bassman OT. It is running 6L6S and a 5u4. Kinda like a blonde bassman with reverb. Not your typical deluxe. Just a couple questions lately the volume pots have been really sensitive. Little tapering it’s zero or ten lol and cracking a lot. Insanely loud but it’s just the volume pots. All the other pots are dead quiet. The faceplate is getting more hot then I’d like.
     
  2. Wally

    Wally Telefied Ad Free Member

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    Did you buy the amp that way or did you do/have the mods made? It sounds like it is a 1x12 AB763 2x6L6 reverb amp....just exactly what Fender never built and what many people think would be the most valuable BF Fender IF it had been built. It is not a blonde Bassman imho.

    It is odd that both channels’ volume pots would have gone wild at the same time. Tech time. If you do tech work, open it up...make a voltage chart....check solder joints on those pots. What pots are there in the volume spots?
     
  3. The Grim Peeper

    The Grim Peeper Tele-Holic

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    Would a AB763 be tube rectified? No the mods were done by another tech and my tech retired recently Bob k in landenburg so I’m looking for a new tech. I can take plate volt and bias and I’m good at soldering and simpler stuff but my troubleshooting knowledge is more limited. I was thinking it maybe a grounding issue because when I tap the tip of a plug against the amp input jacks I get that knocking glass sound.
     
    Last edited: Jan 22, 2020
  4. The Grim Peeper

    The Grim Peeper Tele-Holic

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    80798626-2897-4C76-89D2-3B96F6DAC4EE.jpeg 7CA00BAA-4377-4C9B-A14D-05054F68DC5B.jpeg CA3A0837-F89C-445E-883F-DF6DFC7E8A5D.jpeg C5F54C30-A25E-4C77-AC2F-517053C25F83.jpeg
     
  5. Wally

    Wally Telefied Ad Free Member

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    the AB763 Super was tube rectified....a GZ34 in the BF circuits and 5U4 in the Sf circuits introduced in the summer of 1968. What has been built there in effect is a Super Reverb with a 4 ohm OT, which is operating at a mismatch with a single 8 ohm speaker....unless you have a 4 ohm speaker in it. I do not like mismatches to the high side because I like to push an amp. Ommv
    If you can take voltages, you can do some chopstick tests. I would start with voltage measurements. Make up a voltage chart...and do some chop sticking. You may find a bad coupling cap on down the line? Like I said, both channels acting that way is odd IF the amp did not act this way until recently.
     
  6. The Grim Peeper

    The Grim Peeper Tele-Holic

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    It’s running a 8 ohm v30 as a speaker. Im pretty sure it’s a 4 ohm amp. With a bandmaster reverb pt and a bassman OT I’m not sure what a voltage chart means but I guess I could get a reading on the plates and bias reading. I always bias a 60 percent dissipation. I’m not that great at tracing the circuit I just haven’t done it enough. What exactly do you mean by chop sticking I have a couple good books but I need a mentor lol.
     
    Last edited: Jan 22, 2020
  7. The Grim Peeper

    The Grim Peeper Tele-Holic

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    I just read about chopsticking. Trying that always made me nervous. As a suspect a loose ground that probably a good first step. I assume a fully rubber made stick would do the trick?
     
  8. The Grim Peeper

    The Grim Peeper Tele-Holic

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    8D2DD5FA-8B58-4E04-98F6-6F5E28CD2C8B.png
     
  9. The Grim Peeper

    The Grim Peeper Tele-Holic

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    So this is the correct layout?
     
  10. milocj

    milocj Friend of Leo's Ad Free Member

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    A Fender layout would be better because that one shows a more modern grounding variation. Your amp still has the BF style grounding.
     
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  11. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    If you don't know how to discharge the high voltages in the amp and inspect it safely. You are best off finding a tech to help you.

    Odd for both vol pots to act the same. Kinda sounds like DC is getting to them. I am guessing from the limited info given. I would think a tone stack caps failed but having tone stack caps on both channels fail at the same time is unlikely.

    Maybe preamp tube sockets or the fiber eyelet board. Could be some of the wiring running under the board.

    What is the weather like. Humidity can let the electrons flow thru the board. How often do you play the amp?

    Hot faceplate, scratchy pots. DC is my guess.

    Try different 12a_7s. Look at the socket solder points.

    The amp has had a lot of work. Look for solder balls between the fiber boards and where the wires are soldered to the eyelets. Big gobs of solder can collect under there. The OT and choke have non-stock mounting points under the board, maybe something is making contact under there.
     
  12. Wally

    Wally Telefied Ad Free Member

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    Since he said he was not unfamiliar with taking voltage readings on a live circuit, I suggested that making a voltage chart.
    I am hoping he understands the safety precautions since he has been in touch with a live circuit while making voltage measurements.
    grim, a chopstick is just that...an actual chopstick...or a small diameter dowel..or a plastic stick...anything that is non-conductive that will allow one not poke, prod, and ‘chop’ points in the circuit to find certain problems. This problem may be something simple, or its could be something odd enough to baffle a person.

    https://schematicheaven.net/fenderamps/super_reverb_ab763_schem.pdf
     
  13. trxx

    trxx Tele-Holic

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    Those transformers are really shoehorned in. Looks like a wicked amp though.

    Too much heat at the faceplate? There shouldn't be any significant heat there. I would want to check first that the chassis hasn't somehow become live. After that, is the heat localized to a specific area?

    On the volume jumping, have you inspected joints at the pots, input jacks, and elsewhere?
     
  14. trxx

    trxx Tele-Holic

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    I forgot to mention that my super reverb was demonstrating similar touchy volume knobs until I touched up some joints (understatement; those joints were hideous) at the front panel volume pots and jacks.
     
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  15. The Grim Peeper

    The Grim Peeper Tele-Holic

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    Ok I’m going to go over all the solder joints with a fine tooth comb. Maybe clean the pots and sockets. If that doesn’t help Then I will fire it up and chopstick around.
     
  16. schmee

    schmee Poster Extraordinaire Silver Supporter

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    I have found that other things CAN effect how a volume pot acts. Chopstik that board. But be aware, boards can be noisy without issues sometimes. But I do have to say, I had this same issue in my 65 Deluxe and in the end replacing the worn out volume pot fixed it.
     
  17. trxx

    trxx Tele-Holic

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    I think that is what someone attempted to do in my amp. Unfortunately, that person's soldering skills were poor, leaving the volume pots having something of an intermittent connection upon further inspection, and the end result being that the volume was very touchy, jumping from very low to very high. If Grim Peeper has an ohm meter (particularly a needle style) and some jumper wires, it would be easy enough to test the pots for smooth operation.

    But I would be first concerned with the mentioned heat at the faceplate before looking at anything else. That sounds to me like something very wrong and potentially dangerous.
     
  18. schmee

    schmee Poster Extraordinaire Silver Supporter

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    Yeah, to tell the truth I haven't felt any of my faceplates, but with all that iron packed in, I wouldn't be surprised if heat is built up after a while. My modded Princeton Reverb with his style/size of trannys would make the wood top of the amp pretty warm!

    On my Deluxe Reverb, my volume pot would jump fast and one tiny area had a dead spot finally so I replaced it. I guess 50 years is enough!
     
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  19. trxx

    trxx Tele-Holic

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    That's a good point on the transformers.

    On volume pots (note to Grim Peeper), when testing for dead spots with an ohm meter, you will see a sudden jump on the needle or the numbers (go very slow if using a digital meter so as to see the numbers more easily change).
     
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  20. trxx

    trxx Tele-Holic

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    I wonder if the heat issue has always been there with that amp, if it suddenly happening, or maybe Grim just took notice of it while looking at the other issue.
     
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