01-07-2017, 08:36 AM
The circuit is in the 1967/68 edition of 'Radio & Television Servicing' on Pages 217/218, Trevor, and may also be available from UKVRRRDF either as a download or on Paul Stenning's DVD (Not sure how to post links on here!). It's a quite conventional 2-stage amp., built around an ECL86, on a metal chassis. I could sketch out the relevant part and post in on here. Apart from any copyright issues, I can't scan the circuit from the R&TV Servicing book without taking the page out, and I don't want to do that!
Regarding the fault, points taken, but I fitted a new 2 x 32uf can, and have also replaced the pentode cathode's bypass capacitor and (bias) resistor, plus other resistors which were mounted on the valveholder, and the HT filter/screen grid feed resistor, which was out of tolerance, 'that' capacitor, and the one across the o/p Tx primary. Possibly, as Boater Sam suggested over on UKVRRRDF, the valve develops heater/cathode leakage as it warms up.
Regarding the fault, points taken, but I fitted a new 2 x 32uf can, and have also replaced the pentode cathode's bypass capacitor and (bias) resistor, plus other resistors which were mounted on the valveholder, and the HT filter/screen grid feed resistor, which was out of tolerance, 'that' capacitor, and the one across the o/p Tx primary. Possibly, as Boater Sam suggested over on UKVRRRDF, the valve develops heater/cathode leakage as it warms up.
