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?

[David Roper]

Have you gotten the scope out yet?

[Eric H]

Check the value of the cap across the Oscillator coil, make sure you used the correct value.

I have mistakenly put in a .00* instead of a .0* on several occasions, that will throw the frequency so far off you can;t adjust it out.

Another possibility is someone in the past adjusted the Horiz coil to compensate for a bad cap and when you replaced it it's now way off.

I don't know this chassis or have a schematic so I'm guessing that in addition to the regular Horiz Hold control on the front , it has an adjustable Horiz coil somewhere in the Oscillator circuit, a coil with a slug most often, find that and give it a tweak and see what happens.

[Eric H]

And yes, a bad Mica could be throwing it off, there have been more and more reports of failed Micas recently, even they don't last forever I guess.

[Radiotronman]

When you say horizontal coil, do you mean the horizontal frequency, drive or linearity controls?

[Electronic M]

Frequency of course.

[Eric H]

What's the model number of the set?

[Radiotronman]

321k47

[Eric H]

Here's an example, it's an Admiral but probably older than yours and a different model, same idea though.

Coil L20, B1 would be the adjustment I would look for, and make sure the capacitor C61 across the coil is the correct value for your set.

[old_coot88]

The squealing noise is sometimes of mechanical origin. If it's still there, try tightening the flyback clamp nuts and mounting hardware.