630 chassis low HV?

[N2IXK]

Restoring a Crosley 9-408 (RCA 630 chassis clone), and have the set working pretty well except for a somewhat dim image with excessive blooming.

HV checks at 8.2 kV with no load (Should be 9 kV per service data), but gets pulled down to around 6 kV when brightness is set to normal viewing level. Have tried swapping 1B3 and 6BG6 tubes to no avail. Drive signal and cathode current waveform on 6BG6 looks good. Am testing with a 5AXP4 test CRT, but adding additional HV filter capacitance to simulate the 10BP4 doesn't increase HV as I thought it might.

Any suggestions where to go from here? Width and horiz linearity look good, so sweep circuitry seems to be working pretty well.

[Kevin Kuehn]

Have you checking your HV directly on pin 2 of the 1B3? Possibly the 1M resistor in series with the HV lead?

[dieseljeep]

Is the large resistor, R209 in the HV cage good?
They refer it as horizontal linearity control, but it has a bearing on the boost.
The one in my 621TS is open. The sweep circuit is similar.

[N2IXK]

Yes, measuring HV right at the top of the doorknob cap, which is tied to the 1b3 filament.

R209 good, and set on the center tap (default).

[nasadowsk]

Check the flyback carefully. Had the same issue on a magnetbox TV of the same era, was the flyback had a bad HV winding

[Penthode]

Originally Posted by Kevin Kuehn

Have you checking your HV directly on pin 2 of the 1B3? Possibly the 1M resistor in series with the HV lead?

Kevin has a made a good point. The 1Mohm resistor is subject to overloading if in the past the 2nd anode lead was accidentally shorted to ground.

If unloaded you are getting 8.5kV and it drops when the brightness is turned up, it would appear the 1 Mohm has drifted upward in value..

it is easy to check: pull the 1B3 and mesure from the socket to the 2nd anode lead.

[N2IXK]

Originally Posted by Penthode

Kevin has a made a good point. The 1Mohm resistor is subject to overloading if in the past the 2nd anode lead was accidentally shorted to ground.

If unloaded you are getting 8.5kV and it drops when the brightness is turned up, it would appear the 1 Mohm has drifted upward in value..

it is easy to check: pull the 1B3 and mesure from the socket to the 2nd anode lead.

I am measuring the HV upstream of the 1M resistor, directly at the 1B3 filament.

The 1M and 3.3 ohm resistors both check OK with a DMM. I may replace them anyway as it looks like I will be digging into the 1B3 socket wiring anyway looking for leakage and possibly swapping a flyback to test.

[dieseljeep]

Originally Posted by N2IXK

I am measuring the HV upstream of the 1M resistor, directly at the 1B3 filament.

The 1M and 3.3 ohm resistors both check OK with a DMM. I may replace them anyway as it looks like I will be digging into the 1B3 socket wiring anyway looking for leakage and possibly swapping a flyback to test.

The 3.3 ohm, I would leave, but the 1 meg I would change or eliminate it completely.