Admiral Telebar help

[Radiotronman]

I'm restoring an Admiral Telebar set for a fellow collector. The set has a high pitched ringing noise from what seems to be the flyback area. The original flyback had a cracked phelonic board, so I replaced it with an nos flyback. The noise is still there with no hv. Is this a horizontal oscillator issue causing this? I have recapped this chassis too.

[Eric H]

The H Oscillator's probably running way off frequency causing the noise, it'll also kill the HV if it's too far out.

Does adjusting the H Hold control change the pitch of the noise?

[Radiotronman]

Yes, adjusting horizontal changes the pitch of the noise, but it does not go away. I guess I'll start checking resistors around this tube?

[M3-SRT8]

Yup. Check the resistors in the Horizontal Oscillator. They're frequently way out of spec. Caps, too.

[Electronic M]

If the usual caps, resistors, tubes bit don't get it working then the horizontal section may need adjusting. IIRC admiral subscribed to the same synchroguide H osc system RCA did, so it should require the same kind of setup....Get the waveform peak just a bit higher than the hump and make sure peaks are as far apart as the H sync pulses.

[Radiotronman]

I tested all resistors around the horizontal oscillator and didn't find any resistors way out of tolerance. There are three mica caps on this 6SN7 tube, could one of these being leaky kill the circuit? What else could cause this noise and kill hv?

[M3-SRT8]

Originally Posted by Radiotronman

I tested all resistors around the horizontal oscillator and didn't find any resistors way out of tolerance. There are three mica caps on this 6SN7 tube, could one of these being leaky kill the circuit? What else could cause this noise and kill hv?

Ooooh, yeah. Micas in the Horizontal circuits are prime suspects now. They take a beating there.

[Radiotronman]

I replaced a few micas around the horizontal output tube and a couple resistors, but no improvement. Pin two on the horz output tube is supposed to be 305v, and I measure 250v. The mica cap on the horizontal lock coil is a 3900pf mica, which I don't have. Any more ideas?

[M3-SRT8]

It could be an IF stage. When the noise starts try tapping each if tube.

I had a 721 TCS that had these symptoms and it wasn't a horizontal sweep or synch problem. Swapped out a video if tube and it was fine.

I'm reaching here, but, there it is.

[Electronic M]

Originally Posted by Radiotronman

The mica cap on the horizontal lock coil is a 3900pf mica, which I don't have. Any more ideas?

3900pF = .0039uF...Get a film cap...If you don't have one that is close tack 4 .001 caps in parallel for temp.

[Kevin Kuehn]

Originally Posted by Radiotronman

I replaced a few micas around the horizontal output tube and a couple resistors, but no improvement. Pin two on the horz output tube is supposed to be 305v, and I measure 250v. The mica cap on the horizontal lock coil is a 3900pf mica, which I don't have. Any more ideas?

Which Sams are you using?

[dieseljeep]

Originally Posted by Electronic M

If the usual caps, resistors, tubes bit don't get it working then the horizontal section may need adjusting. IIRC admiral subscribed to the same synchroguide H osc system RCA did, so it should require the same kind of setup....Get the waveform peak just a bit higher than the hump and make sure peaks are as far apart as the H sync pulses.

That chassis doesn't use syncroguide! Many models did, but not that one.
I don't remember what they called that circuit. I always seemed to have grief with that circuit. Synchroguide seemed to be a little easier to troubleshoot.

[Kevin Kuehn]

Sams lists Admiral model 321k47 in both 117-2 and 135-2. The circuit in 117-2 really does look like RCA's Syncroguide, no?

[Radiotronman]

So, any ideas on why there is no hv?

[David Roper]

Have you gotten the scope out yet?