Quote:
Originally Posted by nasadowsk
Once had a blanker issue on a CTC-25 clone cause low h output current....
|
It was a temporary issue, 6LQ6 cathode current is now dipped at 175 ma., which is still low but after an hour of narrowing the noise inverter issue, the fly is fairly warm which is concerning as always. RCA figured to "box-in" the fly to keep dust and airborne slime off the HV rect, etc. The downside is well known and Im considering a reversible modification to address that.
The Tuner-IF-1st/2nd video are cleared of causing the current issue of poor V-H lock, video appears to change every 16 seconds and I verified it by scoping the input to the 6KA8 AGC/Noise inverter. A series of sync pulses float slowly to the left on the scope, with a bunch of odd spikes appearing for an interval. All tubes have been swapped, with no changes noted.
The only clue left is 28 volts of DC voltage on the plate (keyed AGC side) of the 6KA8 where schemo shows 0.2v of DC, which gets the keyer pulse from the fly, the other voltages are within 10% of RCA schematic I'm using. I went after a few electrolytics including the 2mf on 6LF8 screen bypass and 40 mf on the AGC control, still no improvement.
I highly suspect the 560K and 22M resistors around the 6KA8 and in particular, ANY capacitor coupling on the flyback pulse leg.
12-10-2020, 07:32 PM
Hybrid Mode
