Re: Marconiphone 855 Silent on 49m
Well, I tried another X63 and a 6A8G with same fault. I then tried a (probably new) X63GT and it worked on 49m for a few minutes then went silent again. The only valve that works reliably on 49m is the 6K8G. Comparing the voltages and currents between the X63 and 6K8G gave the following results (no aerial - Trader Sheet predicted values in brackets):
X63 Mixer Anode 262v (243v); Mixer Screen 78v (75v)
X63 Osc Anode 124v (178v) (non-oscillating; at 41m with valve oscillating Va=166v)
X63 Osc Anode current 4.8ma (4mA) (non-oscillating; at 41m with valve oscillating Ia=3.9mA)
6K8G Mixer Anode 265v (243v); Mixer Screen 82v (75v)
6K8G Osc Anode 118v (178v)
6K8G Osc Anode current 5ma (4mA)
Strangely the oscillator anode voltage has dropped dramatically from when I first measured it (see first post). Next I'll keep the X63GT in place and reinstate the osc anode feed resistor back from 27k to 15k.
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