Quote:
Originally Posted by turretslug
What is the value of R25 Ben?- I can't see it on the Trader sheet! (I may of course have overlooked it). That'll give you the cathode current in the output valve, which should be around 42mA- at the moment, it looks as though main HT current is somewhat excessive judging by the 139V across what is quoted as the 1400 ohm field coil. There's a bit of detective work needed to suss out whether it's because the output valve is taking too much current, or whether it's because of something else amiss. So far, the DC cathode voltages for the other valves earlier in the chain don't look too far out of kilter, except that I'm puzzled by the large AC voltage on V4 cathode (in particular)- even if there was oscillation resulting from instability somewhere, the cathode bypass capacitor should prevent too much AC component being apparent here.
Colin.
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R25 is 410 ohms on the sheet, actual measurent out of circuit was 459 so it has gone a bit high.
The speaker is a replacement magnavox item that measuures 3k ohms so quite a bit different than the standard