Admiral 14R12 Restoration

[Crist Rigott]

I've done some troubleshooting.

I did a voltage check on the 3 tubes V15 a 6SN7GT Horizontal AFC and Osc., the 6BQ6GT Horizontal Output, and the 6W4GT Damper tube. Here are my findings. 2nd values are my readings:

6SN7GT
1 -2.8v -25v I thinks SAMS made a mistake here. Riders shows -40v.
2 100v 105v
3 -22v -16v
4 -60v -59v
5 235v 190v

6BQ6GT
4 140v 128v
5 -8.6v -8.6v
6 220v 190v
8 5.6v 6.3v

6W4GT
3 320v 250v
4 320v 250v
5 220v 190v
6 310v 255v

The voltages don't look too bad. Most are a little low.

I did hook up my scope to the grid (pin 5) on the 6BQ6GT tube and here is what I got:



I then checked point "C" on L19 per Sams on adjusting the Horizontal Sweep Circuits. This is what I got after I adjusted "B3" on L19.



I don't know what the frequency was but the time dial was set 10us.



Here is a picture of the schematic showing the area:



I also ohmed out the fly-back and it checked out pretty reasonable.

EDIT! I remembered that I can hook up my frequency counter to my O'scope and I then adjusted the Horizontal Frequency "B2" to get 15,734 cps.
Another EDIT! I added the voltage on the 6BQ6GT Pin 8.

[Crist Rigott]

Is there any way to test what's going on with the flyback? Like seeing the voltage from the 6BQ6GT plate cap? Like measuring the voltage there? Everything I've checked so far checked good. I'm getting about 3Kv right now and have a faint raster. So I am getting some HV, just not enough. I don't have a flyback checker. How can I check the door knob cap? I'm trying to find out why my HV is so low.

Thanks for your help.

[Kevin Kuehn]

Your horizontal drive signal basically looks good, but your boost voltage is 70 volts low originating at pin 3 of the damper, which is why some of your other voltages are low. What is your scopes volts per division setting when you measured the signal at the grid of the horizontal output? Have you by chance tried another damper and HV rectifier?

[Kevin Kuehn]

How does your 210 volt supply read at the fuse(M2)?

[edit] Don't forget to make sure your dag coating is grounded good, as I don't see any other HV filter cap going to ground.

[old_coot88]

Have you subbed the 6BQ6 yet? You van sub it with a 6DQ6 in a pinch. The 6W4 can be subbed with 6AX4 or 6AU4.

You failed to list voltage on pin 8 (cathode) of the 6BQ6. But on the schematic you indicate 5.6V. Are you still getting 5.6V there? If not, the tube is not conducting (or if it's too high, the tube is conducting too much).

Also try this - with the plate connector disconnected from the HV rectifier, use an insulated screwdriver and see if you can draw an 'air arc' from the connector. If the fly is putting out, you'll get an arc of a quarter inch or more. But don't short it to ground.

[Crist Rigott]

Originally Posted by old_coot88

Have you subbed the 6BQ6 yet? You van sub it with a 6DQ6 in a pinch. The 6W4 can be subbed with 6AX4 or 6AU4.

You failed to list voltage on pin 8 (cathode) of the 6BQ6. But on the schematic you indicate 5.6V. Are you still getting 5.6V there? If not, the tube is not conducting (or if it's too high, the tube is conducting too much).

Also try this - with the plate connector disconnected from the HV rectifier, use an insulated screwdriver and see if you can draw an 'air arc' from the connector. If the fly is putting out, you'll get an arc of a quarter inch or more. But don't short it to ground.

We'll start with this one first.
I added the voltage on pin 8. Listed voltage is 5.6v and I measured 6.3v.

Will do that arcing test next.

I have subbed the 6BQ6GT and the 1B3GT. Not much change in the HV. Actually what is installed is a 6DQ6GT. When I had good HV, I subbed a NIB 6QB6GT and the HV was lower, so I put the 6DQ6 back in.

I also subbed the 6W4 with no help.

[Crist Rigott]

Originally Posted by Kevin Kuehn

How does your 210 volt supply read at the fuse(M2)?

[edit] Don't forget to make sure your dag coating is grounded good, as I don't see any other HV filter cap going to ground.

I got 190v at the fuse. Earlier I cleaned the dag grounding wire mount and just ohmed it out and it shows zero ohms from the wire and from the dag.

[Crist Rigott]

I just tried the HV rectifier cap connector and I got a very healthy purplish 1/4 to 3/8 long arc.

So it looks like my problem might be with the 1B3GT or its connector. There are 2 resistors under the connector.

Could the door knob cap be bad?

[Eric H]

Originally Posted by Crist Rigott

Could the door knob cap be bad?

There's a slight possibility it could be bad and dragging the HV down, just disconnect it to test, the CRT has a Dag coating and performs the same function so it shouldn't be essential.

[Crist Rigott]

Originally Posted by Eric H

There's a slight possibility it could be bad and dragging the HV down, just disconnect it to test, the CRT has a Dag coating and performs the same function so it shouldn't be essential.

Eric,
I just tried what you suggested and disconnected the lug from the bottom where the white/red wires are connected. When I powered up the set, all I got was some arcing sound from the base of the HV rectifier. I moved things around but each time I got the arcing sound so I put it back together. Still only about 3Kv.

BTW, I used my multimeter to measure the door knob cap. It measured out to 630pf but is listed as a 500pf cap.

[Crist Rigott]

Originally Posted by Kevin Kuehn

Your horizontal drive signal basically looks good, but your boost voltage is 70 volts low originating at pin 3 of the damper, which is why some of your other voltages are low. What is your scopes volts per division setting when you measured the signal at the grid of the horizontal output? Have you by chance tried another damper and HV rectifier?

I think the volts per division were 5v.

I tried another damper and HV rect.

Where does the boost voltage come from? It looks like it might come from the flyback. What would cause it to be low.

Just trying to understand and get the voltages where they should be.