CTC5 Drooping HV

[Penthode]

Hi All,

My Whitby suffers from a poor HV supply. I believe all CTC5's have this problem. The DC voltage measures at about 21kV at minimum brightness (no load and with the shunt HV regulator disconnected. Increasing brightness causes the supply to droop to 15kV.

I have gone through the flyback supply. I can find no problem. I can minimize the Horizontal output tube current to 190mA with the efficiency coil. (I ended up slightly misadjusting to see if I could raise the HV a bit.

Today, I tried substituting a solid state rectifier substitute for the 3A3: it is an ECG508 (depicted). The results are promising: I can now adjust the brightness to a level for a reasonable picture and good focus without blooming. There is a noticeable improvement. The photo below is of the set taken with the new rectifier. (Note the color bars are the last remnant of analog TV from our cable provider).

Any thoughts or comments?

[miniman82]

Always wanted to give this a try, as nothing else I've done has made any improvement in the 5's HV output. What's the HV read with bars on screen at normal brightness?

[tvdude1]

Where did buy it? I would also try one.

[Username1]

Makes me think it's in the heater voltage/current of the HV Rectifier....?
Anyone look into this....?

.

[DaveWM]

me too.

[Penthode]

There is no HV adjustment on the CTC5. My set would be at 20kV at minimum brightness with the shunt regular in place. and would droop to about 18kV at average brightness. With the solid state replacement it will stay at 20kV.

I found the replacement on Ebay for $5.99 Buy It Now.

[Phil Nelson]

Is the NTE508 equivalent? There was a recent discussion of those at ARF:

http://antiqueradios.com/forums/view...p?f=3&t=261334

I was going to try one out in curiosity, but my local surplus place couldn't locate one even though it showed up in their online inventory.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Steve D.]

That's a good fix. The color bars look fantastic in a semi bright room setting, and fill out the screen as they should. I would, imo, adjust the contrast just a bit. Is that a 21AX in the set?

-Steve D.

[Findm-Keepm]

International Rectifier also produced a solid state 3A3, the R-3A3. Many HV Tubes got "solidified" - the 1V2 (2aV2), the 1B3, the R-DW4, and the 1X2(2AX2). There's an R-3A3 on ebay, not mine, with one bid right now.

[Penthode]

Originally Posted by Steve D.

That's a good fix. The color bars look fantastic in a semi bright room setting, and fill out the screen as they should. I would, imo, adjust the contrast just a bit. Is that a 21AX in the set?

-Steve D.

Yes that is a 21AXP22A and I have not been able to get the brightness and contrast range before. I reduced the contrast intentionally to push the brightness. Also the Whitby has an unmodified contrast control (eg the original contrast control design changes the Video Output amplifier grid bias) which now will work better in conjunction with the brightness control without blooming.

[ChrisW6ATV]

Originally Posted by Phil Nelson

Is the NTE508 equivalent?

Yes, most if not all ECG and NTE part numbers are the same item. (Sylvania days versus New-Tone Electronics.)

[bgadow]

I have a few of those rectifiers and never thought of giving one a try in my Whitby....I'll be sure to give it a whirl as mine also droops.