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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 in a 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!