Twin Reverb - weak reverb, tremolo works sometimes

Discussion in 'Amp Central Station' started by Bartholomew3, Aug 25, 2016.

  1. Bartholomew3

    Bartholomew3 Friend of Leo's

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    Tech did a re-cap plus JJ tubes, took out the hum control and blackfaced it for balance. Reverb has been weak for some time but works. He said the circuit etc is OK so it seems the tank has gone south.

    It works but not like it did 20 years ago. Not the original reverb tank - was a Hammond tank from Canada but had to replace it with an Accutronics way back. Was never the same after that but was OK for many years.

    Also tremolo stopped working after he did the bias. He replaced the opto-whatever, no change so put back the original. I read somewhere that hot bias will stop the tremolo. I don't use it anyways but would like to find the answer. New tech ?

    Comments ?
     
    Last edited: Aug 25, 2016
  2. BobbyZ

    BobbyZ Doctor of Teleocity

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    Did the electrolytics on the board get replaced? A bunch of 25v 25uf caps.
    I've had that fix trem and reverb it certainly can be other things too.
     
  3. Jushden

    Jushden Tele-Meister

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    Try replacing the RCA jack to turn the trem on. On my amp the trem wasn't reliable and upon inspection I found the connections were covered with a yellow buildup/corrosion. I replaced the connector and now it works all the time.
     
  4. strat a various

    strat a various Friend of Leo's

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    I don't think power tube bias affects Twin Reverbs that way. It does on Princeton Reverbs, a few other Fender amps, and I believe perhaps a couple of Gibson and Ampeg models, maybe. But not Twin Reverbs.

    If the tech replaced the optocoupler, then something else is wrong in that circuit.

    I had a well-known and respected tech work on my Princeton once, and he honestly didn't understand the "vary-bias" type of vibrato that Princeton Reverbs use, so it's conceivable that your tech isn't up to speed on vibrato circuits, either. Find a different repairman. I'll bet Wally out in Lubbock could figure it out in no time, he knows Fender circuits inside and out. Hopefully he'll be along any time now.
     
  5. Jushden

    Jushden Tele-Meister

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    You could also try swapping v5 out to see if it was the tube that drives the trem. You can test the RCA Jack by attaching an alligator clip to the wire going to the RCA Jack and touching the other end to the outside of the RCA connector to turn it on.
     
  6. keithb7

    keithb7 Friend of Leo's

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    You could keep throwing parts at it hoping for a solution. This often a lesson in futility. Best to get the schematic and troubleshoot the problem properly. Saying that, here is what I found, when trouble shooting a weak reverb. I measured all resistors in the reverb circuit and found one way out of spec. Replaced it and it was back, stronger than ever. Non working tremolo might often be tracked to a bad ground. The tremolo circuit must be grounded to work. It is grounded through the vibtrato RCA jack in rear chassis. Many a tech have shotgun'd all the parts in a trem circuit to repair it. Yet to remain stumped. A conductive fibreboard will have you throwing every part at a repair until you give up and throw it all out the window. ;)
     
    Last edited: Aug 27, 2016
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  7. Bartholomew3

    Bartholomew3 Friend of Leo's

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    Thanx guys - the tech mentioned that the pedal with RCA jacks had to be replaced but when I got home with the amp it worked OK for a while so I forgot about that.

    Appears that may be the problem I overlooked as it's intermittent - a new direction. Have to take it apart and determine why he couldn't re-wire it.
     
  8. BobbyZ

    BobbyZ Doctor of Teleocity

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    Can't imagine why the jacks would be bad. I mean there really isn't much to go wrong with the male RCA jacks on the amp besides get dirty.
    The female ones on the cables get spread out sometimes and don't ground right but can be bent back. Unless they're cheap newer ones made out of poor quality metal.
     
  9. keithb7

    keithb7 Friend of Leo's

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    Real simple fix here. Eliminate the floor switch and test the trem without it. Get an old RCA cord from your basement. We all have 100's from the early 90's VCR era.
    Leave about 2" of wire and snip the plug off. Strip the two wires and twist them together so they are touching. No solder or iron? No problem. Back electrical tape and cover
    up the twisted wires. Insert the new fangled RCA plug into your vibrato RCA jack on your amp. Done. Switch is eliminated. Your Trem should work now if indeed the floor switch was the problem.
     
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  10. keithb7

    keithb7 Friend of Leo's

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    Seen here. I keep a couple in my gig bag. Red for use on Canada Day. Green for St Paddy's day. These will work on any old Fender amp with vibrato. If you are missing a vibrato foot pedal you can use one of these simple devices to engage your vibrato. Easy-peasy.

    [​IMG]
     
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  11. Bartholomew3

    Bartholomew3 Friend of Leo's

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    This is a great idea that I never saw anywhere, am doing it. Have thought about something similar by soldering a new RCA plug but this is way easier. Have about 6 or 7 spare stereo wires for different systems over the years - but not a green one...


    A few months back I substituted the original RCA plug reverb wiring with wire from a stereo system
     
  12. stratwilly

    stratwilly Tele-Meister

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    Hi,
    I am quite new here and I signed in because I have trouble with the trem of my '68 vibrolux and I stumbled upon this thread.
    The trem in my amp works in principle, but if the amp is switched off over a longer period of time (a few hours) then the tremolo is not starting immediately and it needs some time. The first time much longer e.g a minute, then a few seconds, then it is working as expected.
    I already changed the roach, the tube, the 20nF Ceramic cap, and also the 25uF cathode caps around the trem. The resistors values are fine... This circuit drives me crazy.
    Indeed, the fibreboard is wavy because of air moisture over the years...
    Do you have an idea or suggestion what to do in such a case ?
    Cheers Willy
     
  13. Andy B

    Andy B Friend of Leo's Silver Supporter

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    Change the (2) .01 & (1) .02 caps in the tremolo circuit. Looking at the amp from the rear they are the 3 caps in a row to the right of the bug.
     
  14. keithb7

    keithb7 Friend of Leo's

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    I have a 71 Super Rev with same symptoms. After swapping everything out, I lived the shot-gun lesson. It still has a delayed start upon initial startup from cold. I suspect a conductive fiber board.
     
    Last edited: Sep 1, 2016
  15. stratwilly

    stratwilly Tele-Meister

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    Wow, these are fast replays - thanx guys, - this is a great forum !

    @Andy B
    jup, changing the last two o.01 caps is not a big deal - finally I will try this, but after reading keithb7's comment ...:(

    But "hope dies last" ...
     
  16. keithb7

    keithb7 Friend of Leo's

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    New bright orange caps, new roach, cathode cap and resistors, new RCA jacks and tube in vibrato circuit as seen here. Delayed vibrato engagement persists.

    [​IMG]
     
  17. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    "black facing" has nothing to do with balancing anything. It's a process to recreate an older circuit - not a "result". I've sen "correct" blackface jobs by techs that didn't know HOW to balance the phase inverter or to check plate voltage before setting the bias.

    The simple answer - if your tech actually gave the amp back to you with poorly working them and reverb (BTW, those orange drops are ridiculously large and unnecessary for tremolo caps) and didn't know what to do with the "bug" demand a FULL refund and take the amp to a QUALIFIED tech.

    Whoever you took it to didn't have a clue, and now you are chasing you tail over work that should have ben performed. That's horrible, and makes me feel terrible for techs everywhere. I just don't know what gives some people the idea they are qualified to do tech work.
     
  18. keithb7

    keithb7 Friend of Leo's

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    I'm open to suggestions from a qualified tech, as to why my trem has a delayed start up under certain conditions. All parts in trem circuit replaced. Known good tubes swapped in. Pots, caps, resistors, roach and jacks new. Voltages and resistance tested. Solder connections inspected re-flowed. Aside from replacing the entire fibre circuit board I'd love to fix it. Thanks.
     
  19. boredguy6060

    boredguy6060 Poster Extraordinaire

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    He may not like me throwing his name in the mix but,
    If you can get a message to Tubeswell, he is an authority on Fender trem circuits.
    He's on the other side of the world, from here anyway.
    He is well known on many forums as the go to guy on these kind of issues.
     
  20. stratwilly

    stratwilly Tele-Meister

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    Just a short update:
    As discussed in another thread - today I took a decision:
    I don't care about this collectors and "vintage don't touch" voodoo. I want my amp smooth sounding and in perfect working order.
    Therefore I changed also the last 4 bypass caps in the pre amp section and I thought this is a good opportunity to change the two 0.01 ceramics in the trem unit.
    Now the tremolo is working and I am happy.
     
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