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Working on a DSL50 head with no output. I have searched and read the other posts on common problems - this head has already had the V1/V2 DC heater voltage bridge rectifier upgrade and the 16-ohm ground jumper at the output jacks. There is good signal out the effects send to another amp and there is no change if you jumper the effects jacks. All preamp and power amp voltages are fine. I checked the plate voltage resistors on the preamp tubes, all ok. Output tubes are biased at ~35 mA per tube. I injected a 2KHz sine wave and traced through the preamp clean (Classic) channel - I end up with about a 1.8V P-P signal coming out of the cathode follower (V3) to the PI (V4) at clip (channel gain and volume both almost full up). The PI then puts out about a 15-18V P-P AC signal to each of the output tube grids - is this a reasonable maximum drive level? At this value I get mV at the output jack/speaker, I need to go back and measure the AC volts at the input to the OT. Appreciate any insight.
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Generally speaking, I look for a Vac grid signal (max) that is around double the grid bias voltage. -
Thanks - I was suspecting the output tube grid drive needed to be stronger. Round numbers, I should expect 90-100V P-P then. I need to go back and have a closer look at the stages just before and including the PI.Comment
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The output would then be 20 Vac into an 8 ohm load.
20 x 20 / 8= 50 watts.Comment
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