12-02-2017, 08:24 PM
As I said, the metalising was complete, and connected. However, I have sorted it out now, although what I have done will probably not be accepted as a solution! 
On studying the circuit, it appears that the supressor grid of the EF39 (IF amp) is used as a diode anode to produce the AGC. I decided (probably incorrectly), that a malfunction of the AGC was increasing the gain to the state of instability. So - I shorted the AGC capacitor out, thereby disabling the AGC. The shrieking and howling stopped immediately. On 200 Volts HT, the tone was a bit rough, but on turning it down gradually, things began to improve. Finally, the optimum performace was obtained with an HT voltage of only 50 Volts. This gave more than adequate volume, excellent tone and selectivity. This suits me fine, because I can build an isolated PSU providing the required 50 Volts, that I consider a lot safer than the specified 220 Volts HT on a 73-year-old receiver!
I can now concentrate on replacing the wiring. I have already restored the screen dropper circuit on V2 to the original configuration of sharing the screen dropper and decoupler of V1 with V2.
Maybe the condition was caused by the fact that the Westector was faulty, and I replaced it with a gremanium didoe that was probably superior to the Westector when it was working!
Bob
On studying the circuit, it appears that the supressor grid of the EF39 (IF amp) is used as a diode anode to produce the AGC. I decided (probably incorrectly), that a malfunction of the AGC was increasing the gain to the state of instability. So - I shorted the AGC capacitor out, thereby disabling the AGC. The shrieking and howling stopped immediately. On 200 Volts HT, the tone was a bit rough, but on turning it down gradually, things began to improve. Finally, the optimum performace was obtained with an HT voltage of only 50 Volts. This gave more than adequate volume, excellent tone and selectivity. This suits me fine, because I can build an isolated PSU providing the required 50 Volts, that I consider a lot safer than the specified 220 Volts HT on a 73-year-old receiver!I can now concentrate on replacing the wiring. I have already restored the screen dropper circuit on V2 to the original configuration of sharing the screen dropper and decoupler of V1 with V2.
Maybe the condition was caused by the fact that the Westector was faulty, and I replaced it with a gremanium didoe that was probably superior to the Westector when it was working!
Bob
