I did my first Cap Job (Drip Edge Bassman)

Discussion in 'Glowing Bottle Tube Amp Forum' started by DannyStereo, Dec 24, 2018.

  1. DannyStereo

    DannyStereo Poster Extraordinaire

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    *WARNING - I am in NO way, shape, or form an expert on Electrical anything, and this is not meant to be advisory. Do NOT work on your tube amp if you have ANY doubts about your skill level*

    Hello all,

    A few weeks back I worked out a trade for one of my amps for this 1968 Bassman plus cash. I’d been jonesing for a Bassman, and it just worked out.

    It was a bit noisy, so I knew I had to dig in. Took the cab cap off, and sure enough - IMG_0991.JPG IMG_0992.JPG

    Filter caps had gone.

    Now, I’ve biased and done general service on a BUNCH of amps, but never replaced any components. So off to internet land I go to do my research. Also, I considered taking it to a tech and in fact was going to, but I figured at SOME point this is something I NEED to learn. Plus, my next door neighbor is a close friend of mine and an electrician. I figured, worst case I buy him a six pack and have him help.

    So I ordered the parts online, Rigged up an alligator clip to the chassis to the a 100k resistor and tested with my multimeter every step of the way to make sure the voltage had drained. I tested a LOT, and I mean a LOT. More so than necessary, mainly because I don’t want to die.

    I went slow and took my time, and an hour or so later, all the filter caps were replaced. Nothing else appeared to need replacement upon visual and ‘tap with a pencil’ inspection, and she is now singing like a bird.

    Much like the first time I replaced an alternator on a Chevy, the sense of accomplishment was intoxicating. I’m running it into a 4ohm Weber Silver Bell in a 1x12 cab.

    IMG_1004.JPG
     
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  2. Piggy Stu

    Piggy Stu Friend of Leo's

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    I never did this, but I do a lot of other things like this and know how satisfying it is
     
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  3. DannyStereo

    DannyStereo Poster Extraordinaire

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    It was really a LOT of fun. Plus now I know I can do some of my own repairs on my other amps. The goal is to be able to help other local church musicians as well. I already do setups and repair on instruments, I just want to be able to help my fellow worship musicians with amps as needed - especially the younger guys (I’m 31) who play for their youth groups and such.
     
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  4. blues bondsman

    blues bondsman Tele-Afflicted

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    Here are my writings about These amazing amps and a few I upgraded (blackfaced, caps etc...)
    It has had 93664 views , Sadly I lost hundreds of pictures thanks to Photo Bucket.

    https://forums.fender.com/viewtopic.php?f=12&t=82488

    I had that same feeling with every one, they amps come alive with a little love eh !
     
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  5. Piggy Stu

    Piggy Stu Friend of Leo's

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    Not sure about helping others with electricity. Reminds me that no good deed goes unpunished
     
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  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    What about the electrolytics on the board? Specifically the cathode bypass caps and bias cap? Those should also be replaced as part of a standard service. Death cap/grounded cable should also be done.
     
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  7. DannyStereo

    DannyStereo Poster Extraordinaire

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    Someone had already replaced the cable and removed the death cap before. Why they didn’t also replace the filter caps I’m not sure? The bypass and bias caps appear in good shape so I left them original. I may convert the AB165 ‘hum bias’ circuit to a true bias circuit when I get some free time, but for now it sounds great as is! I’ve also tinkered with the idea of making the Bass channel into a Marshall-esque channel.

    I also will need to replace the power tube sockets. They have some chips and small cracks.
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Most of the techs on this forum will agree there is no way to tell by looking at caps that they are good, and original caps in an amp of that age need to go. Just throwing that out there.
     
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  9. DannyStereo

    DannyStereo Poster Extraordinaire

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    Man I am going to have to give this thread a good read!! It’s funny to me how little is know about the Black Line Drip Edge fenders. Essentially the same as their black face counterparts at least until mid 1969, but fetching much lower prices.

    Now, I sorely resent ever letting go of my Blonde Bassman with the Presence knob. What a dumb thing for me to do.
     
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  10. DannyStereo

    DannyStereo Poster Extraordinaire

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    Gotcha. Like I said, I’m limited in my experience, so I will get around to it eventually ( i have the parts already, just need the time).

    For those of you who don’t know me, I am a Social Worker for Child Protective Services, foster parent, and father of 3. So ‘free’ time is kind of non-existent.
     
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  11. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    As mentioned above, appearance is irrelevant. Filter and bias caps should be replaced roughly every 15 years, as they have a service life of 15-20 - which manufacturers don't talk about. Bypass caps on fixed bias amp handle very little voltage and only a few types re regularly off spec after 15 years - the cardboard and "whale" dual-lead caps. White Mallorys rarely fail. And regardless - failure does not damage the amp like it can with a filter or bias cap. There's just no reason to do a wholesale replacement of low-voltage bypass caps.

    The bias cap absolutely should be replaced! And usually with a 100uf/100v. Doesn't affect the bias but is safer for the amp.

    As cathode bypass caps are rarely bad I recommend testing them. Most modern meters have a test function for caps.

    You DID re-bias the amp after the cap job, right? IT will have definitely changed.
     
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  12. DannyStereo

    DannyStereo Poster Extraordinaire

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    Yes definitely biased! I put a fresh set of 6L6s so I addressed it while I had the chassis out. Thanks for the info! I think the bias cap in there is 50v. Not sure why they built them that way? It would seem that the higher value would be, as you said, a little safer.
     
  13. Wally

    Wally Telefied Ad Free Member

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    I’ll jump on the dogpile!!! Lol.....IMHO, the bias cap/s should be replaced along with the filter caps. Most of us would have added a pot to adjust the bias voltage, too. It can simply be added to the circuit while keeping the balancing circuit...best of both worlds.
    Re: blackline Fenders. Danny, the Bassman had the same circuit in it from January, 1965 until May, 1968.
     
    Last edited: Dec 25, 2018
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  14. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

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    [/QUOTE]

    Actually...appearance is EVERYTHING.
    If your electrolytics appear to be more than 15 years old, they need to be replaced ;)
     
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  15. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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  16. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

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  17. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    :lol:
     
  18. DannyStereo

    DannyStereo Poster Extraordinaire

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    Anyone else rocking a Drip Edge bassy?
     
  19. 68silverw/black

    68silverw/black TDPRI Member

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    I have a '68 that I play through a closed Avatar cab (4 Ohm) loaded with two Celestion G12H Heritage speakers. It is a rock and roll machine.
     
    Last edited: Jan 3, 2019
  20. keithb7

    keithb7 Friend of Leo's

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    I serviced a 66 BF Bassy this summer past. Caps, tune up, you know all the regular stuff. I cranked it up and tried a couple of my guitars thru it. I was impressed. It defines the word crunch. I suspect your black line SF Bassman is the same. Very good, solid rock 'n roll amps.

    I wonder sometimes why Leo & Co. used different width heads for the Bassman and the Bandmaster? The matching cabs then had to have different spacing for the head mounts. The two amps are very close in size, however are not. The cabs and heads are not interchangeable. Seems like things could have been more efficient and easier if they shared the same head cab, and speaker cab.

    [​IMG]
     
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