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Old 21st June 2012, 09:04 PM   #21
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hi, i'm getting the feeling you may be lacking some basic electronic skills.
please be careful around the power supply, the primary is 110V in the u.s. and the secondary is up to 250V.
you need to examine amplifiers with an oscilloscope - not a test meter.
You should be looking at waveforms on the D.C. rails, not the transformer.
The rail voltages are in the region of +/- 36V, +/- 50V and +/- 124V.
If you accidentally short these rails with your probes, you'll melt the probe, risk damage to the amp and your eyes.
This really isn't an amp for beginners - its just too complicated and dangerous.
take care,
jonathan
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Old 23rd June 2012, 12:26 AM   #22
srinath is offline srinath  United States
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I sound more scatterbrained than I am. I have yet to give myself anything worse than a headache working on these amps and I have fixed near about 50 vintage and HT amps. I may not be formally electronically educated and up on terminology ... but I know what a switching transistor does vs a power transistor etc etc.

Cool.
Srinath.
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Old 23rd June 2012, 01:30 AM   #23
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Hi,
I was wondering if it is possible to try a "GE-MOV" metal oxide varistor across the triac. This will filter any noise coming from the triac. You most get one depending of the working voltage.
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Old 23rd June 2012, 03:05 AM   #24
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This is way above my head. However, I've owned about 5 different M400(a|t) over the years. I killed one that had a slight hum, back in the 1990s. I am inept! When I first hit upon this thread, I wondered if it could be (but turns out to not be) one of the other types of hum this model can do: the unit itself will hum or buzz like a transformer (silent at speakers, but the cube would hum).
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Old 23rd June 2012, 03:20 AM   #25
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I would try a GE MOV Mouser part no. 576-V220ZA05P $0.36 cents acorss the triac.
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Old 23rd June 2012, 03:27 AM   #26
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Default MOVs

The "knee" of the conductance of MOVs is typically around twice the peak AC line voltage. They usually only target large spikes on the line, so I doubt you'd get much effect, if any, on low voltage hash and spikes.
There are other voltages available but nowhere as common as 130 or 275V types but as they don't have a sharp threshold of conduction, any attenuation will still depend on the size of the spikes.

The killer is that a nominal 130V rating MOV doesn't clamp until >320V!
http://www.eeel.nist.gov/817/pubs/sp...Superalpha.pdf
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Old 23rd June 2012, 07:32 AM   #27
djk is offline djk
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A triac for a Carver must be of a type selected for good 4th quadrant firing. If the gate threshold voltage has any asymmetry the transformer core will buzz and saturate.
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