Ace and Steve’s Big Vintage Summer Adventure: Update No. 3: The Long and Winding Road by Steve Graham Progress of a sort, on the Mactone front. Perfect and as new? Probably not. The conundrum one can face with obscure vintage gear, like the X-21, is finding reliable and reasonably complete information. I had a hard time wrapping my head around the X-21’s circuit. Not having a schematic, a fair bit of time was spent looking, head scratching and making voltage measurements. The power supply wouldn’t look out of place in a pair of stereo EL84 power amps. There are eighteen large capacitors filtering the B plus voltage! All of these capacitors retain the almost 400 volts B+ long after turn-off. The X-21 could have a fatal bite for the unwary. PLEASE READ THE FOLLOWING IF YOU HAVE A MACTONE X-21 Safety notice: If you are thinking of working on it, be very careful. If you are unsure of what you are doing, DON’T DO IT! The high voltage supply is almost 400 volts! All of the capacitors seen in the picture below store a lot of energy and do so for more than an hour after the [...]
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