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Old 25th June 2012, 04:06 PM   #931
Salas is offline Salas  Greece
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Quote:
Originally Posted by stajo View Post
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
Good advice, but most DMMs will catch very low band problems only.
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Old 25th June 2012, 04:27 PM   #932
stajo is offline stajo  Sweden
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Good advice, but most DMMs will catch very low band problems only.
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.

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Old 25th June 2012, 05:02 PM   #933
Salas is offline Salas  Greece
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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.
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Old 25th June 2012, 05:48 PM   #934
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Originally Posted by cjkpkg View Post
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.
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".
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Old 25th June 2012, 08:40 PM   #935
disco is offline disco  Netherlands
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Originally Posted by cjkpkg View Post
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?
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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Last edited by disco; 25th June 2012 at 08:43 PM.
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Old 26th June 2012, 01:50 AM   #936
cjkpkg is offline cjkpkg  United States
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I got up close to it tonight and the tubes are resonating "audibly"...The lower resistor is bypassed with a film cap...I would have to check the value.
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Old 26th June 2012, 06:17 AM   #937
stajo is offline stajo  Sweden
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And gridstopper, what type and value and is it tight to the pin (short distance between resistor body and grid pin) ?
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Old 26th June 2012, 08:20 AM   #938
stajo is offline stajo  Sweden
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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.

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Old 26th June 2012, 09:58 AM   #939
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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
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Old 26th June 2012, 10:11 AM   #940
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I'm not daring to remember Buzz's mess up with tube PSU

that reminds me of my youth

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