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In Reply to: Re: Have you measured the voltages and do they match that marked on the schematic? nt posted by Vinnie on March 5, 2007 at 03:36:38:
Per the schematic you displayed in the OP, there is NO input voltage shown. There are anode & cathode voltages shown for both stages.
Follow Ups:
I finally figured out why I thought there were no voltages shown. I wasn't looking at the one posted here, I was looking at the one I used to build the phono pre. It must be an older version because it doesn't have the voltages on it. I just got through checking them and the 260 vdc going into the phono pre is right on, but the voltages at the plates are a little low. I got 138 instead of 145 on the first stage and 144 instead of 160 on the second stage. Still, that seems to be "in the ball park" as Joseph said, and I would think it should at least work. Same with the cathodes, they read 1.16 & 1.18, a little low but should still work. I also went back through the entire schematic and I can not find anything wrong. I also checked all the component values and they are correct. Danged if I know what is wrong!!
Disconnect the 1st stage from the 2nd and put a signal into the grid of the 2nd stage. Does it work then?
Found out last night that the right channel is ok after I switched a couple of wires that were reversed. I will try to isolate the trouble in the left channel tonight. I figure I can jumper from the right to the left to have a working signal to use for a tracer. Thanks for the tip.
Vince
OR, use the CD player as a signal source to check the 2nd stage. OR a smallish-value capacitor with one lead held between thumb & fore-finger, other lead touched to control grid of EITHER stage as a signal tracing tool. If stage is OK, a loud Hum wil be heard thru the speaker. BTW, this held-capacitor signal tracer may be used to check any stage of any audio gear (with ss, touch to transistor Base) & when inserted into the input jack will check entire circut. A cap value of say 0.01uF to 0.05uF is suitable. Body capacitance provides the Hum signal.
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