From the very basics of AC-powered heaters/filaments directly to DC switching supplies for heating the is one hell of a leap; No mention was made of filament-winding centertaps nor using resistor pairs (or a trimpot) to balance heater supplies and lower hum, nor the technique of biasing up the filament supply with a DC voltage borrowed from elsewhere in the amp (such as the output tube cathode-resistor voltage). Installing a switching supply, especially one chosen to be over-rated for 10 amps, strikes me as a complicated solution to amplifier hum, a problem that anyone who has studied tube amp circuitry and design going back nearly 100 years would know how to prevent in much simpler fashion: with good layout and grounding.
@robertjamesrobson2907
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Thanks for raising some good points. It's always hard to know how deep to go with these things, but a filaments video delving into some of the legacy techniques you've mentioned as well as some other tips and tricks is warranted. I sometimes forget that there are still a lot of people building legacy designs incorporating technologies that have been supplanted by more practical developments. But for people who are understandably tired of carrying around enough iron to power several amperes worth of filaments at 50 or 60Hz, the leap to a reliable, lightweight and compact SMPS is a one worth considering. Good layout and grounding are always essential as you say, but circumventing some of the problems that layout techniques can only reduce to tolerable levels is often a better way to go.
@goodun2974
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@@robertjamesrobson2907 , the Achilles heel of SMPS design is capacitor failure from high-frequency ripple. Whenever a manufacturer contracts out to have SMPS power supplies built in China or Asia, invariably the caps used are junky electrolytics that bulge and leak and fail prematurely. Not to mention that most SMPS supplies weren't designed to deal with the excess heat that develops inside a tube amp chassis. Which doesn't mean that it can't be done to a higher standard, but if you look at the myriad of modern tube-based guitar amp designs on the market these days, hardly anyone builds them to the highest possible modern state (which is why we see Fender and Marshall lamps with cheap circuit boards that become conductive, leading to noise, unstable bias, and thermal runaway). Mostly you get overly-complex amplifiers that are the musical equivalent of a Swiss army knife, doing a lot of different things half- ass tonally but not necessarily doing any of them very well, and with the downside that they become far more complex, complicated, failure-prone, and expensive to repair (take a look inside a Mesa amp, for example). I don't see any upside to increasing the complexity and unreliability of a power-supply circuit by adding additional parts, in order to shave off 5 pounds of carry-weight from a guitar amp. The inexperienced and uninformed are easily awed by complexity, but a genius is impressed by simplicity. Anyway there is no reason why somebody can't take the tail end of the heater supply and rectify and regulate it just for the first couple of preamp tubes, which is typically where most of the hum and noise gets into the signal path. Beyond that point, much of the hum is going to be canceled out if it's a push pull amplifier. Class A amps, or high-gain amps, might require more work to keep noise levels down. Most of the techniques for good tube amp layout and design that date back 60 or more years are still applicable to "modern" designs, and if a company's designers/engineers aren't sufficiently versed in how things were done in the past to be able to not repeat those mistakes in the present, then they have no business being In the amplifier business. They're just as likely to end up inadvertently building an oscillator ! It's also worth mentioning that from the Fifties onward the 12AX7A was purportedly manufactured with filaments that are spiral wound in opposite directions for each side of the tube, which is supposed to make them essentially humbucking in operation. Hopefully modern Russian and Chinese tubes do this as well, although the design specs for classic American and European tubes are sometimes seen as little more than a suggestion to overseas manufacturers nowadays.
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