Admiral Telebar help

[Kevin Kuehn]

Originally Posted by dieseljeep

Riders shows that model number to use a 21B1 or a 21L1 chassis.
The schematic shown is not the right one.
The OP should only use the chassis number. Model numbers mean very little.
Riders volume # 13, page 13-1. There was a multitude of changes made throughout the production run.

I suppose the .0039 cap was the clue to reading between the lines, but then again one never knows for sure what changes have been made to the set before someone comes on here asking for help.

[Radiotronman]

I've checked every resistor and cap around the horizontal oscillator and horizontal output tubes. Any out of tolerance resistors were replaced. I also tested the flyback and it tested good on my tester. I still get no hv. These Admirals are usually easy to restore. What am I missing and what's going on here?

[EdKozk2]

Tom asked you to check the damper. You should be getting at least 250 vdc on pin 5 of the 6W4. Pin 3 of the 6W4 should be about 415 volts, this is your B+ boost voltage. Make sure there is continuity through all the terminals of your linearity coil. These voltages are the same as your boost voltage and they pass through pin 1 of the flyback to the plate of the 6BQ6.

[Radiotronman]

Ok, thanks. I will take those readings and report back tonight. I used my BK Analyst and injected horizontal drive voltage to the cap of the 6BQ6. I now get an arc off the cap of the hv rectifier, but no arc at the second anode button on the crt. I still don't get a raster, but can hear the hv running with the analyst for the first time. I also checked and replaced any out of tolerance resistors in the base of the hv rectifier while I was at it.

[bandersen]

OK, so if you've got an arc at the HV rectifier cap, either the rectifier isn't working or it's being loaded down by a short or there's a break in the HV lead. Easiest to try first is swap out the HV rectifier. Also check for continuity in the HV lead going to the CRT.

[Kevin Kuehn]

Also check the resistor in series with HV lead. It's probably hiding under the HV Rectifier socket.

[Radiotronman]

Kevin, I replaced the 470k resistor in the hv socket that runs to the hv lead to the crt second anode. I also tested the 2.7ohm resistor on the hv filament and it was right on.

[EdKozk2]

When you say " injected a drive signal to the cap of the 6BQ6" ,did you mean plate cap ? I would think in order to properly test the circuit you would inject the signal to the junction of R85 and R83 which is connected to the grid pin 5 of the 6BQ6. Also if your 1B3 is OK, and all your voltage tests , along with continuity checks, the you may may have a bad 500mmf doorknob. I had to replace them in the two Admirals I fixed this spring.

[Electronic M]

Originally Posted by EdKozk2

When you say " injected a drive signal to the cap of the 6BQ6" ,did you mean plate cap ? I would think in order to properly test the circuit you would inject the signal to the junction of R85 and R83 which is connected to the grid pin 5 of the 6BQ6. Also if your 1B3 is OK, and all your voltage tests , along with continuity checks, the you may may have a bad 500mmf doorknob. I had to replace them in the two Admirals I fixed this spring.

ED, the B&K analyst family can drive a set's flyback directly at the output tube plate lead...I've got a B&K 1077 analyst and have used it that way several times.

[EdKozk2]

Originally Posted by Electronic M

ED, the B&K analyst family can drive a set's flyback directly at the output tube plate lead...I've got a B&K 1077 analyst and have used it that way several times.

HiTom, I figured since he threw in a new flyback that it would be better to check the operation of the horizontal output tubes associated circuits.

[old_coot88]

The Analyst will drive the grid too, right?

[Radiotronman]

Ed,

How did you know those doorknob caps were bad? What symptoms did they cause and were they killing hv? Where did you get replacements?

[EdKozk2]

Originally Posted by Radiotronman

Ed,

How did you know those doorknob caps were bad? What symptoms did they cause and were they killing hv? Where did you get replacements?

The second anode voltage was too low and causing the HV rectifier arc internally. Had close to no HV on the other set also, so I just changed it any way. I replaced the doorknobs with 15kv ceramic disk caps, .001mfd. I had to modify the mount and connections to use the cap on the underside of the chassis. Special attention to lead placement and spacing is required when modifying. You don't want intermittent arcing. Only make this change if your sure about the doorknob. Don't forget that troubles with vertical output transformer can load down the B+ boost voltage too.

[Radiotronman]

I did a continuity check on the hv cable last night and could not get continuity from pin 7 on the hv rectifier socket to the hv button. I did get continuity from pin 4. The cable ties in with a 470k resistor off pin 7. They might have used pin 4, since it's an unused pin as a junction point for the cable and resistor, but shouldn't I have gotten continuity from pin 7, where the other leg of the 470k resistor should attach? I'll take apart again tonight and check this. There was some sloppy repair work on this set before I got it, maybe they hooked something up wrong while repairing. Instead of a 470k resistor in the hv socket, there was two 1meg resistors in parallel (making 500k). I can't imagine that was original from Admiral, but maybe.

[Kevin Kuehn]

I think you're right about pin 4 being a tie point, because there's no pin 4 or 6 on a 1B3.