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Old 3rd April 2013, 03:54 AM   #1
scrimpu is offline scrimpu  United States
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Default Bias vary tremelo help needed

I have a Traynor YSR-1 that is need of new EL34 tubes. How do I go about checking the bias after I get the new tubes?. Its a fixed bias, no adjustment pots, and it has a bias vary tremolo which is something new to me.
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Old 3rd April 2013, 03:57 AM   #2
Enzo is offline Enzo  United States
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Turn the trem off, and measure tube current as you would for anything else. The tube currents at the plate voltage yields dissipation, which is within limits or not. Or do you just not know about measuring bias current in general?

If the trem works, unless the thing sounds real weird, I'd assume it was OK.
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Old 3rd April 2013, 06:50 AM   #3
Tesla88 is offline Tesla88  Italy
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Schematic
http://www.lynx.bc.ca/~jc/moddedYSR1.gif

Set tremolo to 0 or remove V7 and measure plate current and plate voltage , so you get actual plate dissipation...
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Old 4th April 2013, 09:42 PM   #4
scrimpu is offline scrimpu  United States
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I understand how to take the measurements, I am unclear as to how to make the actual adjustment. Fixed bias is new to me. I would think changing R49 would do it but I haven't the experience to be sure.
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Old 4th April 2013, 11:12 PM   #5
Enzo is offline Enzo  United States
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SInce the amp has no adjustment, we would take the readings to determine that the tube bias fell within safe limits, and that is it. The way to alter it would be to make R48 variable. But the amp itself won't care if the bias is set to some super precise readings. All the amp wants is tubes that don;t red plate or be running so cold the crossover distortion is huge.
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Old 26th April 2013, 10:55 PM   #6
scrimpu is offline scrimpu  United States
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What value pot and resistor do you recommend to make it adjustable? I have a 25k pot and a 25k resistor, would that be ok to put in place of R48? If so would this arrangement allow enough variance to run EL34 or 6L6GC tubes?
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