A little advise needed, Fender BF Twin RI

Discussion in 'Glowing Bottle Tube Amp Forum' started by 24 track, May 22, 2019.

  1. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    I've been asked to take a look at a 65' BF Twin RI ,
    the amp has been retubed, and has a crackling sound, that happens when the standby switch is activated, I plan to clean the pots , and the tube contacts, tension the tube holders etc and check for bad caps resistors etc , now I know these have a PC board and not an Eyelet board , is there any thing else I should look at before I get too deep into these repairs ?
    I dont have the amp yet (to work on ) and havent seen or heard it yet , I'm just looking for the usual suspects to bear in mind , it could be an easy fix or it could be stupid because of the PC board having to be removed entirely and full component replacement ,

    given that the amp gurus all live on this site any sugestions will be appreciated!

    I said I would look at it , every thing works well appearently, so the problem seems intermittent but constant which is why I think its a physical or dirty contact issue , and if its too much work, I wont touch it,

    I have one of these amps my self and 85 watts is a lot of juice
     
    Last edited: May 22, 2019
  2. Milspec

    Milspec Friend of Leo's

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    Crackling sounds when at idle often indicates a bad preamp tube. Even new tubes can have a failure. Give them the old tap test and see if one sounds different or you hear noise through the speaker.
     
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  3. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    thanks, great,
    I'll try that tomorrow when i get the Amp, the symptoms souhd physical not electronic component ( so far) , so maybe a general maintenance is all thats needed.
     
  4. Dacious

    Dacious Poster Extraordinaire

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    Pull the number 1 preamp tube on the right looking at the rear - it's only the Normal channel tube, so that won't work. Sub it into every other position.

    Retry switching from standby. That should isolate a bad tube, but not a bad board connection.

    Keep an eye on the power tubes - any internal flashing or sparking in time with the crackling isn't a good sign. that's chassis-out time.
     
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  5. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    good stuff , I will use that as well, thanks!
     
  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    An amp is an amp. They are all the exact same. I don't do different troubleshooting on a modern PCB amp than I do with a vintage hand wired amp. Isolate the issue by either pulling tubes or signal tracing and go from there.
     
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  7. Andy B

    Andy B Tele-Afflicted Gold Supporter

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    Check the standby switch itself. In older amps they do get flaky. With the power off, jump it with a clip lead and power the amp up.
     
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  8. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    I'll be going out to get the amp soon , I'll post more once I know what I am looking for
    thanks every one for the insight!
     
  9. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    I went and got the amp todayI ran 10 tests with the tubes

    with a known complete replacement of good tubes ( I have the same amp with no issues )

    what the story is when the stand by is on , dead quiet , with the levels down on both channels and the stand by is off the amp has a monster hum and it loudly pops when the stand by is put on, same issue with a full set of working tubes,
    however the cheap chinese 6l6's are really microphonic the 2 mesa 6l6s are quiet no issues , I tried 2 brand new groove tube 12AX7 no difference

    Tubes are not the issue next step open her up and look for bad caps, but i would recommend a full set of tubes at the end of this, thats so far I do more tomorrow
     
  10. Snfoilhat

    Snfoilhat Tele-Holic

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    Not a guru and I'd rather have to build a twin than repair someone else's, but FWIW...

    The language may be an impediment to everyone contributing their best help. Darned standby switches...

    So when the amp is ON and the standby is OFF then the amp is in play mode -- is that how everyone uses the words or do I have it mixed up?

    If it were my job to do, I would leave the standby switch in play mode for the entirety of the repair -- get everything in working order from power off to power on, warmup, idle noise, idle voltages & other measurements, sounding good with a guitar. And only after all that was done tackle the popping sounds or other peculiar behaviors associated with mechanically switching the standby switch. Because it is such a brief action it can't me measured in a sort of steady-state like many other amp functions can. And even 100% working amps sometimes pop. Starting with the pop might lead down a blind alley or get conflated with troubleshooting the rest of the amp.

    Let the standby switch just be an extra length of wire until you're almost done or have followed the trail right back to it.

    Not a guru.

    Good luck!
     
    Last edited: May 23, 2019
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  11. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Fender has said for years in their own service documents that some pop from standby is normal. If it's super insanity loud, them maybe something is up, but fix the amp first like @Snfoilhat says.
     
  12. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    thank you,

    just so were all talking oranges,
    when I power on and the amp is in warm up status the standby switch is activated or ON , when the amp HAS warmed up and I defeat the standby switch there is a monster hum and a severe speaker killing POP when I go back into stand by mode ,

    I ran 10 complete tests dealing with bad or microphonic tubes (No joy )
    I even replaced the full set of tubes with a known good set of Groove tube #2's out of my own twin ( no Joy)
    I opened up the amp and on the circuit boards I found an oily substance in the highlighted areas , indications of an electrolytic cap or caps that has dumped its contents and need to be replaced there is an almost spray pattern to this oily residue or CFC's that have leaked you can see the substance in the highlighted areas

    there is a line of oil going straight across the word Fender and the wrinkle looking laquer in the top right ballon is oil drops same over by the diodes next to the connector on the left, now i also looked at the contained filter caps no issues there , but this now a job for the next few days

    what i did find that the reverb send and returns were reversed , you are correct about the amp first but now I have a direction to go in , the first tests were to familiarize my self with the amp issues as i just got it home today.

    P1012217.JPG
     
  13. Mike Eskimo

    Mike Eskimo Doctor of Teleocity Ad Free Member

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    This is a serious question - not a snarky one : with almost all eras of vintage Twins (Including those that have been serviced/black-faced, are in perfect working order) plummeting toward rock-bottom in value/price , why would someone buy a PCB RI ?
     
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  14. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Mike, you and I will never understand that thinking. But I see lots of threads here where folks are scared of old components. Some may also think new and shiny is better looking (poor misled souls — dust, smoke, and torn tolex are storage units for tone).

    Then too, some may not have a good reliable tech to bring the amp up to spec; or may begrudge the $100-200 that can cost.
     
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  15. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    re thinking about your comments , the reason why the price drop in vintage amps these days probably has something to do with the fact that most of these amps have been serviced by techs ( some not as competant as others) and once the parts fail and have been replaced the amps may function well but are no longer totally vintage any more .

    For me presonally I found mine it was 1 month old the previous owner got it after an insurance claim of some kind , then unfortunately passed away right after the purchase , so I got it for 1/2 price new in canuckian pesos the cheap and i mean really cheap chinese 6L6's were immediately rteplaced with a full set of Groove tube #2's and burned in , it's still 85 watts loud clean fender sound and I got all the box candy that came with a new unit.


    I cant speak for any one else , I did see some design improvements with these over vintage units but not enough to say they are better in any way. personally i prefer to work on the turret boards than the PC boards,
    on the RI All of the pots are mounted on a separate PC board and 3 multi pin connectors so its easy to remove and clean but the quality of the pots are in question and cheaper jacks not switchcraft.
    also the securing metal straps that secure the amp head in place have the nut attached to the chasis saving a great deal of frustration trying to hold the nut on your finger tip to get it started in a tight spot only to have it fall off and drop to the botton of the cab whilst attempting to get those screws started with the other hand.
     
    Last edited: May 24, 2019
  16. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    I found 2 bad caps a (C6) 22uf 25volt that appears to be in some need of replacement

    and a closer look at the filter caps cap ( C31) 300 volt 220 uf is bowed out
    so a major cap job may be in order I will replace them all in th filter cap section.
     
    Last edited: May 24, 2019
  17. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    heres what i found, you gotta love mass produced sloppy construction!

    notice the bowing of cap C31 just ready to dump it's cookies 300 volt 220Uf , I will probably replace both of the resisters R65-66 at the top and bottom of the board as well ( 1/2 watt 220k)

    -4.jpg

    as with any failure there is usually a reason for the failure this one was a cold soldered connection that broke on C 31

    -2.jpg

    the shrink tube lable on C6 has almost pulled off of the top of the cap usually indicative of cap swelling and failure as well

    -5.jpg


    then I found this (sloppy manufacture .....HMM ) multi pin cinnector # 3 was not soldered in to place very well and needs to redone
    I will also check for cold solder on the bottomof the main board when I have it up


    OI000316.JPG


    these are just the obvious issues Ive seen, my recommendation is a full recap including the 500volt 22Uf on the main board, which is tied to the caps in the dog house.

    the oily substance I found was some sort of contact cleaner sprayed into the back jacks of the unit
     

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    Last edited: May 26, 2019
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  18. Dacious

    Dacious Poster Extraordinaire

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    One thing to bear in mind with even Reissue amps - they're approaching 20 years old. And Fender wasn't using the very best quality andin some cases marginal caps.
     
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  19. Milspec

    Milspec Friend of Leo's

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    I agree with you, but the one gain you get with buying new is a warranty. Amps are not cheap and for some, having a warranty covering an expensive tool is worth buying new. The fact that you can buy a SF Twin for the same amount of money (or less) makes buying new seem silly, but after you add in the servicing on that vintage amp, it may not be a bargain. Just different needs and goals I guess. I did buy a Fralin VVT amp instead of a vintage Fender Pro for the 10 year warranty....seemed like a good move to me.
     
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  20. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    I originally had a 65 fender super BF ( 450.00 with a 60's tele ) it by was my favorite amp I also had a BF bassman 50,w/ 2X15's and 2X12 cabs nice amp , but these machines would most likely have to be rebuilt to the Nth degree now and had the crap played out of them by now

    heres my brother playing them

    K.jpg
     
    Last edited: May 26, 2019
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