Last month we discussed buying vintage amps on eBay. Here’s
a request list you can take to the repair shop, along with your
“new” vintage find:
Replace the tubes
Only replace preamp tubes if they are completely
worn out or microphonic. Sometimes old tubes contribute
heavily to that great vintage tone. Return all tubes removed
separate bag. There may be some jewels in there.
Replace the power supply caps
Including the electrolytics, also
found in the bias supply. It’s an essential upgrade in an amp that is
older than 25 years. I will only play through a recently purchased old
amp just long enough to hear it before doing a cap job.
Retighten tube sockets, spray out pots, switches and jacks
with contact cleaner. Try to replace defective parts with exact values
and construction to preserve vintage value.
Don’t replace film caps!
Film capacitors are at the heart of the
vintage amp’s tone. This is an area where some techs can get carried
away. Film caps in the tone and driver stage drift from their
numeric value with age, contributing to the amp’s character. Unless
a cap is completely defective, live with your amp for a while before
making any further circuit changes.
Replace defective or noisy resistors
Check resistors in the
power supply stage, and screen and grid resistors on the power
tubes. Plate resistors on the preamp tubes can cause loud hiss and
crackle noises, but should only be replaced if absolutely necessary
as they can also contribute to the tone.
Finally, retouch any suspect cold solder joints and make sure all
replaced parts are returned to you in a separate bag.
With these areas addressed, you’ll have a vintage amp that’s as
reliable as the latest boutique amp offerings. Remember that
these repairs add up, so figure that into the price the next time
you place a bid!