Hopefully the title means we can talk about dynamically changing PS voltages without attracting any nasties (eg lawyers )
From what I've seen here and elsewhere dropping power is fairly simply done by connecting up a mosfet/hexfet in series with the resistor dropping string prior to the OT center tap but after the first caps. This apparently works "out of the box" for cathode biased amps but needs some further circuitry for fixed bias amps.
One feature that's always made me uncomfortable is the output voltage is usually derived from the wiper of a pot - the pot being wired one side to the PS and the other to a tail resistor. Usually that's about 400V or greater sitting casually on the other side of a panel mounted knob waiting to talk to my sweaty beer soaked fingers.
What you are speaking of is power scaling. KOC / London Power has released new super flexible DC power scaling kits that allow the use of nearly any control pot desired. I believe this kit would resolve any concerns that you may have. Or, wait 'till TUT6 is released and incorporate it into your own design.
If you want a killer volume controller that involves no high voltage (and is very easy to try out), run a 3 Ohm pot in series with (just) your output tubes heaters. You can dial the amp down to way less than 1W and still get a natural sound and feeling. Some people have remarked that this will wear out the tubes faster, but I haven't found that to be the case.
ampdoc1 wrote:If you want a killer volume controller that involves no high voltage (and is very easy to try out), run a 3 Ohm pot in series with (just) your output tubes heaters. You can dial the amp down to way less than 1W and still get a natural sound and feeling. Some people have remarked that this will wear out the tubes faster, but I haven't found that to be the case.
Just my $.02!
ampdoc
Interesting thought - kinda in the "alternative" approach basket along with Mojave power damping (50k pot in series with PI cathode resistor).
Thanks for posting!! I hadn't heard of this one. Certainly easy to try.
I don't know how the Mohave sounds, but it is obviously limiting the preamp signal at the PI stage. My idea leaves the preamp and power amp signals unaltered. Turning down the heater voltage to the power tubes just results in less electrons being boiled off to the plates, no AC signal or DC supply
voltages are changed. To my ear the sound is the same until the output is so low that the speaker itself is not responding naturally.
I came up with this after thinking about what a variac does to the amp. Same principal, but this method only affects the output of the power tubes.
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