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rebuild vintage amp or repair?

Discussion in 'Amps and Cabs [BG]' started by webmonster, Jul 10, 2013.

  1. webmonster


    May 19, 2013
    New Zealand
    I have a valve amp I really like from the late 1960's. It is currently working well and it is quiet.

    Over the years it has had some repairs as expected but its circuitry (all point to point wiring) is largely original, which means that many components are c.45 years old.

    Is this a problem? Am I tempting fate in terms of reliability to keep so many original components in it?

    I like the way it sounds now, and I wonder if rebuilding it and thus replacing lots of components will change the tone/sound.

    Is there a trade-off between originality vs rebuilt; tone-I-like vs reliability?
  2. kdogg


    Nov 13, 2005
    If it ain't broke... . It might be a good idea to let a qualified tech run through the amp on occasion, but I don't see any need to begin replacing parts that are still functioning as they should.
  3. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    I agree and disagree. If it's working fine then why worry? Power supply parts that take a lot of heat/voltage/abuse but don't really impact tone are always a good idea to replace so you know the amp will be robust for a long time are always a good idea. Electrolytics obviously. Tubes if necessary. Other than that, yeah I agree, if it ain't broke...
  4. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Test valves, replace electrolytics, clean everything. Good to go if it sounds right. Some types of resistor degrade, but that's audible if its happening. Done this to dozens of amps, totally my area.
  5. beans-on-toast


    Aug 7, 2008
    To some extent, it depends on the amp. Some are designed conservatively and suffer less stress. Components will last longer.

    If it's a gigging amp and your concerns are reliability, have a tech look at it. At the same time, it is possible that the amp isn't living up to its full potential. It could sound even better. With a vintage amp, I prefer to test the components and only replace those that are far enough out of spec that they need attention. Those out of spec parts could be contributing to that great tone. In terms of the power supply, I like to replace all the electrolytic capacitors. Of all the components in the amp, they have the most limited service life. If it isn't a gigging amp, then even if they aren't up to spec, they might be good enough to leave in the amp. This keeps the amp as original as possible.

    If any parts are changed, label where they came from and keep them. They are a handy reference if the amp is ever going to be restored.
  6. salcott

    salcott Supporting Member

    Aug 22, 2007
    NYC, Inwood.
    I recently got an Ampeg SB12. I took it to my amp guy, who went through it top to bottom. The tubes, all original, tested fine. He replaced the electrolytics, several of which bore the words, "Guaranteed for one year". It was probably about time. The amp sounds the same as before the checkup.
  7. Crater


    Oct 12, 2011
    Dallas, TX area
    The only components that "wear out" are the tubes (valves) and the electrolytic filter capacitors in the power supply. If the filter caps are going bad, you'll have ample warning as the amp will hum whenever it's turned on and warmed up, even without a bass plugged in. If your amp is quiet, then your filter caps are good for now. Eventually pots (tone and volume controls) will fail from mechanical wear, and again, there's plenty of warning because they will get "scratchy" and cut out as they wear out.

    There's absolutely no need to replace any other components - transformers, film capacitors or resistors - unless they fail. I would not even take it to a tech as long as it's working fine and sounds good.
  8. BassmanPaul

    BassmanPaul Inactive

    If it ain't broke don't fix it!
  9. nysbob


    Sep 14, 2003
    Cincinnati OH
    I bought an old ('60s) SB12 in the early '90s and it has never been on a bench since I've owned it. It performs flawlessly, is dead quiet (no hiss or hum), and never ceases to amaze me.

    They surely don't build 'em like they used to.
  10. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Carbon composite resistors degrade with exposure to moisture, fibre circuit boards absorb atmospheric moisture from the air an become conductive. Valve bases become brittle to the point of crumbling. and the contacts corrode and lose their grip. Lots of things in an amp can fail with time other than valves an capacitors. Capacitors in an amp unused for a long time are the only thing that will near certainly need attention.
  11. webmonster


    May 19, 2013
    New Zealand
    Many thanks all the replies.

    The amp is not currently being gigged, but I used to and I'd like the option of being able to gig with it again for smaller venues. I think it sounds great :)

    There is a small amount of hum when it is on.
    The volume and tone pots are stuffed :)
    They crackle and pop when you move them.
    Two of the tone pots are tapped and my tech says that he can't get them anymore.
    I don't have the value(s) close to hand, but does anyone know where they might be available from?

    One thing I am concerned about is could components fail and take out a transformer?

    Is there anything in particular I should look at that could fail at a gig (that I would kick myself for not checking in advance)?
  12. what amp is it? Also if the track is still good you can bring any pot back to life, no need to replace them
  13. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    If you have the right fuses in, transformer is generally gonna be ok unless they are really poor transformers. But the classic is a cap failing, which blows the fuse randomly, and gets 'fixed' with a bigger fuse or foil, and that toasts the transformer.
  14. beans-on-toast


    Aug 7, 2008
    Some hum is normal for most amps. Unless the pots are sealed, crackly and pop can be fixed with a product called Deoxit. It can rejuvenate and lubricate the pots. Try this before replacing the original ones. Some tapped pots are very difficult to locate.

    There is always the possibility of a catastrophic failure that takes out the power transformer. On some amps, plate and cathode resistors are designed to blow if a problem arrises. This is why when replacing parts you should use the right type and wattage rating for these resistors. Trust that your tech does it right.

    An old transformer is at risk because the coating (varnish) on the wires that are used to wind the coils inside the transformer can get brittle and crack. This can lead to arcing and problems. All you can do is use it and make sure that it doesn't get too hot. If necessary, a small desk fan blowing into the back of the amp can help. If a problem does develop, replacements are available.

    In general, I believe that it is better to have a vintage amp in playable condition rather than keeping it simply to look at. If parts need to be changed to keep it playable, don't worry about affecting the value of the amp.
  15. Jeff Scott

    Jeff Scott Rickenbacker guru..........

    Apr 11, 2006
    Out there!
    I totally agree here, unless you want a museum piece down the road.
  16. Steve Dallman

    Steve Dallman Supporting Member

    Electrolytic caps have a working life of 15-25 years. As they age they drift in value, usually up, and in a very sloppy way. As they drift up in value, they drift down in power handling and eventually fail. When they fail they will either open up (hum) or short, and often take other components with them when they short. Replacing them is standard tube amp maintenance akin to changing fluids, filters, hoses and belts in your car.

    Carbon comp resistors often drift and get noisy.

    If I get an amp in with noisy pots that are hard to find replacements for, I will try cleaner/lube first. Often the spray only moves the debris around. Next, I remove the pot, take the back off, physically clean the trace and inspect for cracks or damage. The lube and put the pot back together. Unless damaged, this always works.

    There are few tube amps, no matter how old, that can't be restored and made to sound as good as they ever did.
  17. webmonster


    May 19, 2013
    New Zealand
    A NZ made 'blackface' Jansen Bassman.

    I've sprayed a fair bit of CRC 2.26 into the pots over the years. Quietens them down for a few months.
    Very good to know they (probably) can be rebuilt if necessary!

    I trust him and he has a very good reputation. If anything he is perhaps too conservative; he tells me he could rebuild the amp but an original transformer could go 'pop' the next day.

    Transformers for Jansens are not available off the shelf, but I have found out about a semi-retired gentleman who can re-wind them in NZ.
    The only other re-winder I knew of retired a few years ago when his eyesight deteriorated :(
    It is entirely possible that a very close match could be found with research - I do this with my old cars quite a bit :)

    That is what I want to hear (and it is what I believe too). I was almost dumbfounded to hear that collectors prefer amps in original condition, even if they don't go :confused:
  18. beans-on-toast


    Aug 7, 2008
    I've used CRC (I used to get it for free) and it isn't bad but I believe that Deoxit is a superior product. If you have an opportunity, give it a try. This is the one that I use, 100% concentrate with a needle applicator.

    The nice thing about a transformer is that it can be stripped down to the plates and rebuilt.

    I had a similar amp in the late 60's built by a company that produced modified versions of Fender amps. The transformers were bigger than the Fender ones. THe heavier iron made the tone was rich and beefy.
  19. two fingers

    two fingers Opinionated blowhard. But not mad about it. Inactive

    Feb 7, 2005
    Eastern NC USA
    Beans beat me to the Deoxit recommendation. I use the same stuff with the same applicator. And like most here have said, a good cleaning and a cap job every now and then and you will be fine. Only replace what starts acting up after that.
  20. If the transformer was made decently well, and if other components in the amp behave properly, there's no reason to believe the transformer will suddenly go "pop" at any moment. However, as noted, transformers can be rebuilt.