Its probably layout or error. I never ceased to be amazed how often i miss something simple. Check every component and node. Draw it on paper as you follow it over the board. You might be surprised. I doubt a beoskie psu is noisy. Could be wrong. Fwiw, i found i was using a really noisy transformer for my filament voltage. I think it was having trouble with the current draw. Cheapo Radio Shack.
Does that mean that heaters are lifted to about 70 v above ground? 6V6 should cope with that. Is it DC or AC on heaters?
I think I see that what looks like your cathode bypass caps is very close to the tubes. They get hot wich can affect their condition and reflect back on the tubes if they become unstable. I would keep caps futher away from hot tubes.
Staffan
I think I see that what looks like your cathode bypass caps is very close to the tubes. They get hot wich can affect their condition and reflect back on the tubes if they become unstable. I would keep caps futher away from hot tubes.
Staffan
Hopefully they read 120 Hz ripple tho. All of mine do. Another way of ruling out PS is of course to make a simple c-r-c. Shouldnt be anywhere near described hum. Make sure to make ground connections exactly as on the regulated supply if so.
Staffan
120Hz ripple they will happily read but if its a say 2MHz complex oscillation, no luck to read it. As I wrote before its possibly a typical routing mistake or a bad interaction between PSU and load. Oscillation does sound like aggressive hum when strong. You see a large spray of harmonic noise if you FFT the signal in audio bandwidth also. Other clues are, elevated temperature in active components, intermittent behavior if the oscillation is on verge, i.e. signal comes and goes in various tests. Without a scope, a little AM radio can catch strong noise when about the oscillating area.
Without having oscilloscope, i would guess it is layout or schematic error based. It seems unlikely that a PSU that worked normally before is suddenly causing problems. I have had a semi broken output ground wicause severe hum. You gotta go through it one step a time checking both proper layout as well as proper voltages and operation. Start with PSU and confirm it is functioning as it should,then move through the circuit. Wouldnt be surprised if it turns out to be something "obvious".
When lifting heaters in B+ it's practice to bypass the lower resistor with something from 4,7uF to 10uF.
If possible test without regs in place: 350V to the anode and AC to the heaters. If you still experience the rattle look for a ground loop.
NB The heaters can't be left floating
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Buzzforb had a similar problem. His tubes were "playing music" not his speakers. And he was also into the phase shift worries, grounding signal pin on RCA etc.
It starts at page 50 somewhere. Im not clear about what the problem really was and how he solved it, but Im sure he can tell you.
Staffan
. And he was also into the phase shift worries, grounding signal pin on RCA etc.It starts at page 50 somewhere. Im not clear about what the problem really was and how he solved it, but Im sure he can tell you.
Staffan
