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Re: one output tranny hotter than the other-need advise

If you have a 2VDC scale on your analog VOM you should be okay. I am a little leary of using current meters to measure current in audio power amps. I know that sounds odd, but when you measure as many resistors as I have you'll realise that just a little bit of dirt on your test probes can have a big impact on the measured results. Also, when you measure current you have to put the test probes and the meter in series with the circuit. It's, pretty much, just a problem that I have. I should not, however, dissuade you from investing in a digital voltage meter. I know alot of folks were talking recently about the value of Fluke 'real time,RMS' meters and I have a few of them, but I only have them because I was able to purchase them ridiculously cheaply, and because after 20 years my $20 Archer/Radio Shack digital volt meter finally wore out. Radio Shack meters are pretty good, even the cheap ones. And it is comforting to measure, for instance, the voltage across a 10 ohm/2 watt resistor and measure 0.44VDC but nothing so dangerous as 0.45VDC. Oh, by the way, if you do the math on the stock 44 milliamp bias setting the way I suggested in my previous post, each output tube should be dissipating 9.24 watts. If you multiply that times the square root of 2, you will get around 13 watts which right at the design max of those 6BQ5 type tubes. That last calculation doesn't really mean anything, but isn't it a comforting margin of safety. Nothing like the square root of 2 to make you feel like you're moving in the right direction.
With regard to the heat in Scott amps...Yeah, there's not really much that you can do about that. That aluminum chassis sure is beautiful, and it sure spreads the heat. I have seen the insulation on the wires melt and short under the chassis, simply because that nice aluminum chassis spreads the heat out so well. The fans you were using before is probably a good idea. However, if you can get the bias down to .44VDC across those 10 ohm resistors, at least you will know the heat is not an electrical problem which you could have fixed.


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  • Re: one output tranny hotter than the other-need advise - corerosin 12:14:50 08/18/05 (0)


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