10-08-2013, 07:28 PM
There are two things that seem to stand out regarding your measurements. First the B+ voltage is rather high and second the voltage across R6 is abnormal.
The high B+ could be caused by a lack of load on the supply or a shorted speaker field, which normally would be dropping the voltage to the tubes at least 60 or 70 V. Check the resistance of the field winding and see what it measures. When operating, what is the voltage on each side of the field, measured to ground?
R6 is the cathode resistor for the 6K7 1st IF tube and there is no way there should be 54 V across it. It should be 1K, and with that voltage drop there would have to be 54 Ma passing through it and therefore the 6K7 tube, which is not likely. More likely R6 is bad and increases in value when it warms up. Have you tried replacing R6 as it might be the problem.
Edit- I just looked back at your previous post and saw you measured 278 V on the grid cap of the 1st IF 6K7 ??? Is that right? If so there must be a short to B+ in the 1st IF transformer or associated grid circuit, or the 6K7 has an internal short. Remove the grid cap (with the set powered down!) and then measure the voltage on the grid lead and the 6K7 cap separately to see which is supplying the HV. This might also explain why you have 54 V on the cathode resistor!
The high B+ could be caused by a lack of load on the supply or a shorted speaker field, which normally would be dropping the voltage to the tubes at least 60 or 70 V. Check the resistance of the field winding and see what it measures. When operating, what is the voltage on each side of the field, measured to ground?
R6 is the cathode resistor for the 6K7 1st IF tube and there is no way there should be 54 V across it. It should be 1K, and with that voltage drop there would have to be 54 Ma passing through it and therefore the 6K7 tube, which is not likely. More likely R6 is bad and increases in value when it warms up. Have you tried replacing R6 as it might be the problem.
Edit- I just looked back at your previous post and saw you measured 278 V on the grid cap of the 1st IF 6K7 ??? Is that right? If so there must be a short to B+ in the 1st IF transformer or associated grid circuit, or the 6K7 has an internal short. Remove the grid cap (with the set powered down!) and then measure the voltage on the grid lead and the 6K7 cap separately to see which is supplying the HV. This might also explain why you have 54 V on the cathode resistor!
