Vintage ADMIRAL 19A1 Chassis

[SteveK]

Hello Everyone,
I'm in the process of restoring an Admiral 19A11 electrostatic deflection TV Receiver. It's in SAMS 59-2. Does anyone know at what frequency the High Voltage RF Oscillator (6V6) runs. I want to check this circuit, but not sure of the frequency. Any help, would be GREATLY appreciated! Thanks

Steve

 

[kellys_eye]

Can't find any reference to the actual frequency - perhaps you could measure the L/C values and get an approximation from that mathematically?

 

[SteveK]

Hi Kellys_Eye,
It's funny, they make no mention of it. To me, sounds rather odd. But things back then WERE a bit different. Errors on schematics, parts lists etc. I worked on it this afternoon. Had a condition when first powered up, high voltage very low. Power down, then power back up, high voltage then present. checked the resistor in the feedback circuit which goes to RF Osc (6V6) control grid from ring on 1B3. Should be, 180K. Had gone up to over 2 Meg's! Now incredible brightness from that 7JP4. High Voltage way up now. I'll try some calculations for that osc freq. Won't kill myself though. It's obvious circuit working quite well! Next, change resistors in Vertical output and Osc circuits. Controls are too close to end of rotation. I'll post my progress, as I move along. Thanks much for your reply.

Steve

 

[kellys_eye]

No problem - it's nice to hear from someone that has an interest in vintage items like your TV set. No mean task restoring them as I am well aware.

FYI, I'm a member of a vintage radio web forum (includes all forms of vintage electronic equipment) at http://www.vintage-radio.net/forum/index.php where the membership is extensive and extremely well informed. You could do worse than document your project there as I have no doubt there will be someone with the appropriate knowledge if you require any assistance.

 

[SteveK]

Thanks for the info! I'll check that out.
Looks like possibly, this weekend, chassis will be in it's cabinet. That, will be a TRUE test as with 18 tubes, they'll be some heat buildup in there. The only thing left that I plan to replace is two 39K resistors, and a 10K resistor in the Horizontal Oscillator Ckt. I believe they may be thermal.

 

[JWHassler]

The horizontal frequency isn't 15.7 KHz?

 

[SteveK]

No, I doubt that! There's an RF OSC. in the circuit. I use a neon lamp (while watching raster brightness as well) to adjust the 6V6 Grid ring around the 1B3 HV RECTIFIER. 15,750 KHZ is in the audio range. You can hear the Horizontal Oscillator at that frequency. Highly unlikely that that could ionize a neon lamp.

 

[SteveK]

Oh, to answer your question directly, YES, horizontal Osc frequency IS 15,750 KHZ

 

[kellys_eye]

The HORIZONTAL (scan) frequency is 15kHz but the oscillator frequency used in the high voltage generation circuit isn't - they are separate parts of the circuit.

But I don't think the frequency of the h.t is actually important - as long as you have 'any' oscillation you'll get the required step-up voltage.

The LC circuit in V14 sets the oscillator frequency and the only way to determine it is either loose coupling a DFM to it or measuring the value of 'L' and calculating it as the actual value of L isn't given (other than its DC resistance).

 

[SteveK]

Good morning,
Yes, I agree. The freq there is in the RF range. I'm not concerned about it. I was just curious. Circuit is running fine. High Voltage is fine! VERY bright raster. From what I can see from testing, all I should have to do now is replace 3 resistors in the Horizontal Oscillator circuit. I see a slight frequency drift as chassis warms up. Nothing major. Then hopefully, chassis back in the cabinet!

 

[SteveK]

MUCH THANKS kellys_eye!!

 

[JWHassler]

No, I doubt that! There's an RF OSC. in the circuit. I use a neon lamp (while watching raster brightness as well) to adjust the 6V6 Grid ring around the 1B3 HV RECTIFIER. 15,750 KHZ is in the audio range. You can hear the Horizontal Oscillator at that frequency. Highly unlikely that that could ionize a neon lamp.

"You" can hear it.... not I

 

[SteveK]

Hi JWHASSLER
HEAR the Horizontal Oscillator? Yes, Its not as loud as it was 40 years ago, but i can still hear it. Its way up there, but at 66, I can STILL hear it. 15,750 khz is within the range of human hearing.

 

[kellys_eye]

Yes, I can still hear the 15.625kHz of sets used in the UK (well, old sets...) and I'm pushing 60!

It was only a few years ago (about 10 years) that I could hear bats! Mind you, I've never heard of anyone else that could do this. I'm weird.

 

[SteveK]

That's interesting, I'm not sure if my hearing is THAT good. On this coming Halloween, I'll pay particular attention to that. Then I MAY be able to do a upper level hearing test with an AVAILABLE "test" bat. Right now, none available!

 

[SteveK]

Getting back to my Admiral 19A1 Chassis, I am getting some Horizontal Tearing at top of screen. I've replaced all capacitors and resistors in the,
Sync Separator, Sync Amplifier, And Horizontal Oscillator circuits.
Using the Horizontal Hold, I can correct it, but as the set heats up tearing returns. I believe this is a thermal resistance problem. When set is cold i must return the hold to its original position and as the set heats up again same routine again. I found resistors that WERE way out of tolorance and replaced them in the above mentioned circuits. I'm thinking about Video Amp circuit (6AU6). Although video is pretty good all things considered. I'm using Rabbit Ears, and D/A converter. SIGNAL HERE SUCKS! What I don't understand is I changed all components in the HOLD ckt etc. And this still APPEARS to be Thermal Drift. Any ideas guys??