You have previously reported there is no voltage on the anode of the ECH81,
This may be a silly question, please excuse, but have you got the radio switched to an AM wave band when you did this test.
The black circles with a number identify the switch contacts. See inset diagram of switch at top of circuit.
Contact number 5 being the centre common contact, with contact 6 the supply to the ECH81 triode (AM mode), and 4 being the contact for the supply to the ECC85 (FM mode).
If there is a fault in the switch between contacts 5 and 6 it should be easy to determine.
Have you confirmed the resistance of R12 yet by measuring it with an ohm meter. Sometimes resistors have an invisible crack causing them to go very high value. It would be good if you could confirm if the resistor is close to its specification.
"So, oddly I get 0.013/135 = 10384 R. That's a fair way from 33 K. Or 34 K if you wish. My only explanation is the drop across the windings??"
Who is to say the triode would normally work at 13mA, that figure from the specification of the ECH81 triode is only the maximum it should work at. Have you taken into account R35. I think you may be mixing theoretical max figures and coming up with a theoretical wrong answer.
Keep at it, the answer cant be far away.
Mike
This may be a silly question, please excuse, but have you got the radio switched to an AM wave band when you did this test.
The black circles with a number identify the switch contacts. See inset diagram of switch at top of circuit.
Contact number 5 being the centre common contact, with contact 6 the supply to the ECH81 triode (AM mode), and 4 being the contact for the supply to the ECC85 (FM mode).
If there is a fault in the switch between contacts 5 and 6 it should be easy to determine.
Have you confirmed the resistance of R12 yet by measuring it with an ohm meter. Sometimes resistors have an invisible crack causing them to go very high value. It would be good if you could confirm if the resistor is close to its specification.
"So, oddly I get 0.013/135 = 10384 R. That's a fair way from 33 K. Or 34 K if you wish. My only explanation is the drop across the windings??"
Who is to say the triode would normally work at 13mA, that figure from the specification of the ECH81 triode is only the maximum it should work at. Have you taken into account R35. I think you may be mixing theoretical max figures and coming up with a theoretical wrong answer.
Keep at it, the answer cant be far away.
Mike
