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Restoring an old Twin reverb

Discussion in 'Amp Tech Center' started by Blue Bill, Oct 25, 2020.

  1. Jason Hutchinson

    Jason Hutchinson TDPRI Member

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    I've been looking at your pics and the amp looks pretty original, with a couple of exceptions you already know of. If you're planning to sell, you will have no trouble finding a buyer if you keep it as is. My recommendations are below.

    1 Replace electrolytics in power supply - make sure to note polarity. There are 2 sets of caps there, each with different ratings and polarity. Putting those in wrong will cause damage to the amp
    2 Replace carbon comp resistors under the doghouse with metal oxide (the carbon comps most likely have drifted)
    3 Replace diodes and electrolytic cap on bias board. They are known to fail, and modern replacements are significantly better
    4 Replace electrolytic bypass caps on main board. You can replace the double 25uf caps with 2 single ones. Back in the day they used to be more economical, but are now more expensive.
    5 Install grounded power cord - notes below
    6 Bias the tubes
    7 Clean the controls
    8 Thoroughly test, and replace components as necessary
    9 The output plug does not appear original. They originally had a black cap on the back with a "F" on it.
    10 Replace speakers with originals (optional)*

    The hole in the chassis for the power cord is small, and you would need to find a power cord that fits the hole without drilling it out more. I would keep the cord black, as it was originally so it doesn't stand out. The courtesy outlet should not be changed out for a 3 prong. They started putting the 3 prong ones in during the CBS/silverface era. Since the chassis will be grounded, it is not a shock risk. The ground switch can stay disconnected, and the "death cap" can probably remain in place as long as its bypassed. Most techs remove it though. Other things to consider is that some techs use the j-hook method when replacing components. That is seen a sloppy workmanship and should be avoided. The reverb driver should have the proper fasteners installed so it looks original from the top. I wouldn't worry about the knobs being perfect. You definitely would not want to switch them out since the new ones are different. The originals have a set screw at 10. They are pretty hard to come by.

    *Original speakers are really hard to come by
     
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  2. Jason Hutchinson

    Jason Hutchinson TDPRI Member

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    His videos are very informative. Lately, I think he's been getting picky about taking on new projects.
     
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  3. Mark1406

    Mark1406 TDPRI Member

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    I have briefly looked at some of the posts. Some are alarming to say the least. Pulling all the caps out is a bad suggestion, definitely replace the filter caps and think about modding the first stage of filtration to two 220uF in series. You are going to replace these caps anyway so why not get added performance from the amp?

    Fender did this very mod to their 65 reissue Twin Reverb amp.

    I wouldn’t replace the blue Molded caps, these are a desirable cap to have in an amp. SoZo has tried to clone these caps, Jupiter does the yellow Astrons which cost a fortune.

    I would turn the amp on and see what happens, if you are concerned remove the valves and turn the amp on. Then put the valves back in and give it a try.

    Also try asking this question at The Amp Garage Forum. It’s a good place to ask these sort of questions, and perhaps more relevant than a Telecaster forum.

    Regards

    Mark
     
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  4. fatz treeboy

    fatz treeboy TDPRI Member

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    twins, i own two..... my advice is to replace the Jensens.... which is the dead oposit of what other posters posted :) ...... to me one of the most fun mods to do w/ a twin is trying new speakers..... i ended up w/ two Tone Tubby Alinco Reds..... to me they seem to mellow out the tone nicely....
     
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  5. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    :lol::lol::lol::lol:

    Hi Crunchy, I think you may be referring to the bare wires sticking out from under the doghouse . Looks like those are grounding wires:

    123_0509.JPG
     
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  6. Wally

    Wally Telefied Ad Free Member

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    it would be good to know exactly what wires are causing you to suggest this. IF you are referring to the leads coming from under the board in this picture, those are leads that are going to ground on the brass ground8ng plate.
    4EEC9218-0062-47EF-AC20-116A5E11BF18.jpeg

    Also, FYI, most would not refer to these as ‘orange caps’ but rather as board electrolytics or cathode bypass caps. Orange caps is a term that is applied to certain Sprague film capacitors that are..well...bright orange and are used in tone and coupling cap positions.
     
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  7. Yuro

    Yuro Tele-Meister

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    Agree with 10-over. I've got one of these old Twins. They're ridiculously heavy. If you're going to keep it in a studio or you have Egyptians to haul it for you...or you have a fork-lift and a loading dock, then OK, keep it. Otherwise, a Pro Reverb or Super Reverb are nicer to live with. At low volume, Twin and Pro sound exactly the same. Pro is 40 watts and about 20 lbs lighter.

    Twins make great keyboard amps and they are the standard for clean power, but how much of that do you need? Twins can get so frikking loud without actually sounding any different.

    Anyway, my take. They're nice amps. They're not terribly valuable because not many people want to deal with the weight of them. But if you have specific plans, fix it up the way YOU want and play it for another lifetime.

    BTW, "mismatched" speakers can sound great in these things. I have a Jensen Neo on one side and a green frame Jensen like yours on the other side of mine...on purpose.
     
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  8. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    Thanks SoK66. So many decisions to make. I like the idea of having a accessory outlet, but then again, I never seem to use them. Does anyone have a source for 3-hole replacements?

    Hi Franblanc, I stayed up way too late last night watching a bunch of YT vids, got some good tips. Back in the 80s, I worked as an amp tech, part time for a few years, while working full time as CE at a radio station, so I've cleaned out and fixed up a few dozen old amps. I've forgotten a lot, but I'm fairly confident that I at least know what not to do. My plan is to replace all the electrolyte caps, then see how it sounds, before doing all the disc caps.
     
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  9. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    Thanks Jason, these are some sensible and useful suggestions. 1, check. 2, good idea. 3, another good idea. Does anyone know where to find the specs on these diodes, or the rectifier diodes? 4, check. 5, I'm thinking I might drop by Home depot and get a power tool cord, thinking they may have a nice durable jacket and plug. 6, check. 7, check. 8, check. 9, Yep, I may look for a replacement. Or not, we'll see. 10, again, I'm thinking I should wait and see how everything sounds once it's fired back up. I'm not that picky about speakers, as long as they aren't crap.
     
  10. OneOcean

    OneOcean TDPRI Member

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    Since this a player amp (not a collector's piece) and some have already been replaced, it is fine to replace the electrolytic power supply caps. Keep the originals in a baggie and keep with the amp. I would definitely avoid replacing the blue tone caps. Only replace those individually if it is showing physical signs that it is bad. Those original blue caps are a significant part of the amp's value. If you do decide to replace the blue caps, please send them to me!
     
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  11. J. Bonkosky

    J. Bonkosky Tele-Meister Silver Supporter

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    Replace all of the electrolytic capacitors (use sprauge, F&T, or Nichicon), Add the grounded power cable, change the bias supply diode, and instal new metal film B+supply resistors. You will have an amp that works and is safe enough to sell. Best of luck to you.
     
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  12. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    Thanks Mark. I'll look into the series cap mod, interesting idea. I'm planning to keep the blue molded caps in place, unless one tests bad. I'll also look at the AG forum, thanks.



    Egyptians, :lol::lol: I'm seriously considering replacing the ground switch with a 1/2 power switch, cause, you are correct, where will I ever need such high decibel loudness?
     
  13. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    You're top on the list!

    Thanks J! I think I'll use F&Ts.
     
  14. lavrgs

    lavrgs TDPRI Member

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    If you check an inflation calculator $200 in 1985 is equivalent to about $480 today. I don't think you could buy a similar twin for that today, so anyway you look at it you're money ahead. Good luck.
     
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  15. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Re power cable... measure the hole and the existing cable. Do you have strain relief pliers? Cheap versions from eBay will do the job. The strain relief should be sized to the hole. For cable, and home use rather than stage, 18 or 16ga SVT is just as good as fatter SJT, and yeah, not too long.
     
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  16. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    I ordered 2 NOS Jan-Phillips 12AT7s from thetubestore.com, $40 with shipping. I'm thinking maybe instead of shopping for an ESR meter, I'll pop for a new quartet of 6L6s. That raises more questions, like which ones? Where to get good ones? There's a hit-or-miss aspect to tubes, isn't there? There's a guy here in Maine that advertises advanced tube testing services, maybe I'll call him. If anyone has suggestions on which tubes to consider, I'm open to suggestion. The current tubes, which I've never changed, are 2 GEs,
    a Phillips, and a Sylvania. The amp, as I recall, sounded perfect with these tubes, just like a TR should. Maybe I'll leave them, people say, "Don't fix it, if it ain't broke.", right?

    I got in a couple hours of cleaning this morning, toothbrush, q-tips and rags. Thanks again y'all.
    123_0512.JPG
     
    Last edited: Oct 27, 2020
  17. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    Thanks KF, I'm a sucker for the notion that fatter gauge power cables are better, it may be folly, but, I'm older than this amp and a little set in my ways. I'm looking for a suitable 14ga cord, then I'll order an appropriate strain relief grommet from amprepairparts.com, along with a bunch of stuff. They even have the little trim washers for the back panel screws, which always seem to go missing.
     
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  18. Powdog

    Powdog TDPRI Member

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    I agree with those who have said don’t do anything. If you’re looking to flip the amp it’s at its most valuable right now. If I were in the market for a ‘65 Twin THIS is what I’d be looking for. And as far as F&T lytics go I wouldn’t use them in this amp. I’ve replaced them in Twins (and Bassmans) with broken leads. Sprague Atoms have thicker wire and better electrosoldered ends than the F&Ts. Worth the extra investment.
     
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  19. tubegeek

    tubegeek Friend of Leo's

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    For example:
    What if the thing that happens is, a shorted ancient electrolytic cap takes out the power transformer?
     
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  20. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Seriously, I noted the MM cable already. :) And actually, I like your attitude. You’ve been super patient and positive with all the diverse advice you’re getting. Do it your way, make it yours, and enjoy the journey!
     
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