![]() ![]() ![]() A polypropylene cap in the second position would be a worthwhile upgrade. The electrolytic caps should be 105☌ rated the 100uF values are not excessive. For added reliability, I later changed the single rectifiers to a series pair, each with a 470k voltage equalizing resistor across it. In later builds, I started using UF4007, which could not hurt in the noise department. I used fairly prosaic parts here, but high speed diodes don’t cost very much these days and can certainly be used here to good effect. The output stage B+ supply is an utterly conventional full wave rectified, CLC filtered supply. The device I used was approximately 100 ohms cold, and something under 5 ohms when warm. ![]() An inrush current limiter will be a net positive for reliability. Corcom is a standard brand, but there are many others. These contain an IEC power connector, a crude line filter a switch, and a fuse in a nice convenient package that only requires a rectangular hole for mounting. On the primary side, I’ve become lazy and started using complete Power Entry Modules in my projects. Note the series connection of the two heater windings- you need to verify the phasing of the two windings. This transformer is still available as a new item under the trade-name “Dynaclone.” And of course it’s not critical- any transformer or transformers with similar ratings will work fine. This is my version of the raw supply:ī+ and heaters were addressed with the power transformer taken from the same SCA35 that was the output transformer donor. The critical item is the output stage screens, and our regulator tightens that point up nicely, making raw supply design much less critical. You can do better, but this is at least a good starting point and will do the job. They are quite ad hoc and oriented toward oddball parts I just happened to have in my various coffee cans. To be fair, the raw supplies I’ll outline are OK, but just OK. This should be relatively simple, other than the complication discussed earlier, the need for separate B+ supplies for the output stage and driver. We need to design the rest of the power supply circuitry. We’d better not risk another frontal assault, that rabbit’s dynamite! ![]()
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