rebuild vintage amp or repair?

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.

 

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...

 

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.

 

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.

 

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.

 

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.

 

If it ain't broke don't fix it!

 

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.

 

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.

 

what amp is it? Also if the track is still good you can bring any pot back to life, no need to replace them

 

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.

 

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.

 

I totally agree here, unless you want a museum piece down the road.

 

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.

 

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.

 

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.

 

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.