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grid voltages
DCASAZZA
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Posts: 46
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Joined: May 2008
City: Lake Worth Florida
#1

06-11-2008, 11:16 PM
Any one with an idea as to what g1 volts shoud be for a 650. I have distorted audio (clipped) and suspect the 78 tube is bad but G1 voltages would be a help for the whole set as well.
Dave Casazza
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#2

06-12-2008, 06:57 AM
The reason G1 voltages aren't typically shown is that they will measure differently with different types of meters because of the loading effects.

One approach is to simply use the specs from a tube manual (or online tube data source) http://tdsl.duncanamps.com/ and you MUST use a meter with a high input resistance. Modern Digital meters or VTVMs generally fit the bill and they didn't have them back in those days.

Where there is a cathode resistor involved the cathode voltage will often tell the story but that requires that the tube be in good shape.

Could you describe your distortion a bit more? Normally neither of the 78s would account for that. Have you recapped the set ?
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