• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 line preamp

Jump to Latest
#921
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.
 
#925
Rectified 60 Hz AC gives 120 Hz. Try measure AC with a DMM on your B+. If it shows above or anywhere near 1 volt you have a PSU problem. Should be a few millivolts. If its on the millivolt level, go search on the amplifier card.

Staffan
 
Last edited:
#927
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
 
#929
The PS-1 I am using is also the same board I am using on a phono preamp. VERY quiet.

heaters are regulated DC

I was actually thinking about swapping this PS-1 to my tetra sans and see if it is quiet over there and vice versa.
 
Last edited:
#933
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.
 
#934
cjkpkg said:
The PS-1 I am using is also the same board I am using on a phono preamp. VERY quiet.

heaters are regulated DC

I was actually thinking about swapping this PS-1 to my tetra sans and see if it is quiet over there and vice versa.
Click to expand...

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".
 
#935
cjkpkg said:
here is a question...both PSU's I was using reference the heaters to B+/4. I see the schematic does not show this.

Any thoughts on this as a possibility?
Click to expand...

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 🙂
 
Last edited:
#938
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
 
#939
The advice i have given is from personal expereience, as Stajo suggested. It was a connection error. I had to do jusr as i suggested and slowly move through the correct schematic checking every point. I had one "obvious" connection wrong. Wentfrom singing tube to singing amp🙂
 
You must log in or register to reply here.
Top Bottom