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1974 pro reverb..reverb issue and glassy ringing on some chords..

Discussion in 'Amp Tech Center' started by Randybobandy09, Apr 19, 2021.

  1. Randybobandy09

    Randybobandy09 TDPRI Member

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    Hi all, hope this post is in correct spot. Situation, I have a 1974 silverface pro reverb iv had for maybe a month or so. Got it in a trade. and have been having some reverb problems. Its weak. Basically no reverb until 5 on dial. At 5 its is okay. Things iv done, checked all rca connections, tried different rca cable. Same results, swapped out reverb tubes for known good ones. Same result. Put originals back in. Could a failing tank be the culprit? Or maybe a resistor type deal in the reverb circuit? Any help would be fantastic and much appreciated. Noted V3 reverb tube gets super hot. Super quick. Resistor?
    2nd issue, some chords have a glassy ringing overtone to them reverb just makes the issue more apparent. Swapped v1 and V2 with known good tubes. Basically same result. While tapping on tubes looking for microphonic, all were quiet except (looking at tubes from back) the right power tube, when tapped makes a static, crackle sound. No crackle or static from amp when playing. Other power tube quiet. Same for rectifer tube. Quiet. Most likely installing a SSRetifer. That's aside the point tho.

    Appreciate any help. Thanks to all. for reading.
     
  2. Mexitele Blues

    Mexitele Blues Tele-Afflicted

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    First thing I would inspect would be the cables to the tank. Wiggle them around and listen for a change in the reverb sound.
     
  3. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Have you inspected the tank? Inside there is a pair of springs, and they can break off their connections.
     
  4. Randybobandy09

    Randybobandy09 TDPRI Member

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    Yes, checked that in beginning. No change with cable wiggles. Tips are clean to.
     
  5. Randybobandy09

    Randybobandy09 TDPRI Member

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    No, I have not opened it up yet. Just removed from cover to inspect outside rca connections.
     
  6. schmee

    schmee Doctor of Teleocity

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    1) Yeah, check one of the springs in the tank aren't detached.
    2) Clean the RCA jacks on the amp and cables, especially the outside of the amp jacks where the ends "grip".
    3) My guess is the tank is bad though. You should have too much reverb at 5.

    4) The "far right" tube is the normal channel pre-tube. It could be the tube, socket or more likely a cold solder glob on the heater wires to that socket. If you don't use the normal channel, you can just pull that tube and leave it out.
     
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  7. noname_dragon

    noname_dragon Tele-Holic

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    Half of V4 is the reverb recovery, have U checked that one ?
     
  8. OldPup

    OldPup Tele-Meister Ad Free Member

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    Won't a SS rectifier push up voltages across the amp? I have no clue how this affects the amp. It's just something I have heard repeated.
     
  9. Randybobandy09

    Randybobandy09 TDPRI Member

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    Yes, put in known good tubes in v4 and v3. No change at all.
     
  10. Randybobandy09

    Randybobandy09 TDPRI Member

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    I think so, figured I will be getting it biased at same time due to the switch.
     
  11. Randybobandy09

    Randybobandy09 TDPRI Member

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  12. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    A 1974 anything needs a full service - has that been done?
     
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  13. Randybobandy09

    Randybobandy09 TDPRI Member

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    Yep, when I did the trade, i had the tech look over it. He had a actually been the one to change filter caps and the like. I had him rebias power tubes for more headroom. Also had him remove death cap. Pretty sure the power tubes are going out. Or at least one. Amp sounds pretty mushy at higher volumes. Also need to get those weber speakers out of there big time. Too British for my taste.
     
  14. Randybobandy09

    Randybobandy09 TDPRI Member

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    To that normal channel point.. I know normal amd vibrato channel have different tone stacks and such, tho I noted the normal channel is way way quiter in comparison to vibrato channel.
     
  15. schmee

    schmee Doctor of Teleocity

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    Yeah, thicker sounding too. I've sold some of my Fender Reverb amps and now have a non Rev Pro and a non Rev Deluxe!
    The Reverb circuit is a noise maker for sure, but many amps aren't bad.
     
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  16. Randybobandy09

    Randybobandy09 TDPRI Member

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    It's pretty quiet to be honest. Had way worse. So is this to say it is okay that the normal channel is quieter? I can turn normal channel up to ten on master and vol with no break up. I'm cool with that if its proper. So should I be thinking the glassy ringing is indicative of the power tube?
     
  17. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    I'd swap the power tubes and go from there.
     
  18. schmee

    schmee Doctor of Teleocity

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    Yes, normal channel should be quieter. You have a Master Volume?
    I'm not sure about the glassy ringing, but I think it is likely a tube, pre tube. Is it like feedback ringing? It can be any one of the small tubes. Or are you talking about when you tap the first tube? Pull it and see. It COULD be a power tube feeding back too, although less common than the pre tubes.
     
  19. TwoBear

    TwoBear Tele-Holic

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    Different tone stacks? I was under the impression they were the same or did you mean one has B&T and the other has BMT? Since you had a guy in there already did he check values through the reverb circuit? I don’t have a schematic in front of me but from a shaky memory, isn’t there a strange reverse value pot, Or something like that in the reverb circuit that maybe has been changed out for a ‘close but no cigar’ value?

    Is everyone on the same page in terms of “ when viewed from the back“ Far left is rectifier, then two power tubes, p.i., vib, rev, And finally two pre tubes all the way to the right? If it were me I would be happy with the tube rectifier and the ability to swap out (as long as the power transformer could handle it) and if need be would make SS switchable. I’ve gotten some of my greatest tone out of blackface pros. Are you trying to get it more “Twinlike”?
     
  20. Randybobandy09

    Randybobandy09 TDPRI Member

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    So, when I strum a open G chord. The last note in the chord rings back, does same effect if I pick open G string then 3rd fret G on high e. Swapped out both V1 and V2 no change in chord ringing back. All pre amp tubes are quiet
    When i tap on one of the power tubes I hear a crackle amd some static. Yes I have a master knob. Push pull has been disconnected at some point
     
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