Admiral 14R12 Restoration

[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?

[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.

[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]

Everybody I do appreciate your help with this stubborn problem. I'm sure we'll get it fixed. I just wanted to say thanks for your help.

[old_coot88]

Originally Posted by Crist Rigott

...I moved things around but each time I got the arcing sound....

If you darken the room, it may be possible to see where the arc is.

[Kevin Kuehn]

Have you changed or tested the 1M resistor that's mounted under the 1B3 socket? Those often go very high in value/intermittent, or open. It's the 1M shown in series with the HV lead on the Sams schematic.

The boost voltage is derived by combining the 210 volt supply with the voltage of the lower flyback winding during horizontal retrace. It's a free source of energy during retrace, and so provides a boost to the 210 voltage supply that gets filtered and used for some circuits that work better with the higher voltage.

[Kevin Kuehn]

That was my oversimplified explanation of how boost voltage is generated. It's the best I can do while drinking Jack and Coke at 12:30am.

[Crist Rigott]

Originally Posted by Kevin Kuehn

Have you changed or tested the 1M resistor that's mounted under the 1B3 socket? Those often go very high in value/intermittent, or open. It's the 1M shown in series with the HV lead on the Sams schematic.

The boost voltage is derived by combining the 210 volt supply with the voltage of the lower flyback winding during horizontal retrace. It's a free source of energy during retrace, and so provides a boost to the 210 voltage supply that gets filtered and used for some circuits that work better with the higher voltage.

Kevin,
The the 1meg resistor was changed and still measures 1 meg.

Thanks for the explanation for boost voltage.

[Crist Rigott]

Originally Posted by old_coot88

If you darken the room, it may be possible to see where the arc is.

Just might do that if I have it apart again.

[Crist Rigott]

Well I changed out both resistors (R85 and R86) that were in the connector base of the 1B3GT and used heat shrink everywhere to assure no problems.

I then powered it up with the door knob cap (67) out of the circuit and I still have about 3Kv. I then reassembled the connector and cap and the same thing, 3KV.

I substituted the 1B3GT and still the same thing. I substituted the 6W4GT damper and still the same thing.

Right now I'm at a loss as to what could be the problem

I am thinking of removing the white/red wire that feeds to #1 on the yoke assembly to isolate the yoke assembly. Can I do that without causing other problems?

[Crist Rigott]

I removed the white/red wire to isolate the Horizontal wings on the yoke and then checked the voltage.

With the white/red connected 205v
With the white/red wire disconnected 245v

I disconnected the wire from one of the terminal on the flyback. #8 on the schematic.

Still have to do the Vertical windings.

[Kevin Kuehn]

Your HV rectifier socket looks charred on one side. Or is that dark black some liquid tape? Or possibly it's just the lighting. It might be normal for the voltages to come up without the load of the yoke on the horizontal fly winding.