Quote:
Originally Posted by Humptydumpty
This set has the extra valve fitted for the stabilisation of the power, normal set has 8 valves this one has 9 ,.Phil said it was nothing to do with the power for the receiver.
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No I didn't, Trev. If you look back at the numerous and lengthy explanatory PMs I sent you, you'll see that what I actually said on 9th January was:
"Re the hum, does it vary with the volume control or is it constant? Go back to an earlier message of mine and check the HT voltage. Have you got a multimeter? It could be the main smoothing cap causing the hum but check other things first.
The 0A2 is only a neon stabilizer for the VFO and BFO stages and won’t cause hum."
It might also be helpful to reiterate the advice I gave you in a slightly later PM on 10th January:
"The AC mains goes into the primary winding on the left, and AC comes out of the HT secondary winding on the right. This winding is centre-tapped to chassis. At each end of the secondary winding it says "160" and that will be 160 volts
AC. The next thing is that diodes D6 and D7 chop off the negative half of the AC waveform and leave you with positive-going pulses of DC, which pass into C42 (40uF) which is the reservoir capacitor.
From this point onwards, everything on the HT side is DC.
HT current direct from C42 feeds the anode (pin 5) of the output valve V8 through the primary winding of the output transformer.
This is the 200V voltage you need to check at pin 5 of V8. HT current then passes through R37, a 2.2k 8 watt smoothing resistor, then C40 smooths the HT supply even more, and this HT supply feeds the screen grid of the output valve V8, and the anode of the audio stage valve V7b, and the IF stages. There is a second HT supply, smoothed by R38 and C41, which feeds most of the other stages of the radio. Your stabilizer valve drops the HT voltage and holds it steady at 150 volts to supply the local oscillator and prevent frequency drift.
For now, just concentrate on understanding how the HT supply works and measure the voltage on pin 5 of V8."