CTC16 Flyback Cooling
 

So it looks like Tom (Electronic M) has brought life back to my CTC16 that I regretted buying. I was so mad about it I didn't even want to touch it. Long story there.

The one thing I noticed, and Tom did as well, is the flyback get's very hot after awhile and starts to drip wax. This is about after an hour on for him, and an hour on for me when I noticed it was hot. It's set correctly and Tom will chime in on that, or you can check the last parts of the CTC16 thread and see.

Do RCA Fly's just run really hot? And if so, would it hurt anything if I cut open the flyback box and installed a small computer fan to it externally, to suck cool air though the box so the Fly isn't sitting in there melting it self to death?

They do run warm, but if you have melting/dripping wax, one of three problems come to mind:

1. Too much cathode current through the 6JE6/6LQ6 - should be less than 250mA, preferably the lowest the efficiency (linearity) coil will adjust to.

2. The horizontal drive signal is mis-shapen. Caps, out of tolerance resistors, or a weak 6CG7/6FQ7 can cause the "on" time to increase, which ups the current through the fly.

3. Too much load on the fly - bad/wrong boost rectifier (it requires a "fast" rectifier for Boosted B+, a typical silicon diode won't do), bad focus rectifier (my CTC16 has an R-2AV2 silicon replacement, eliminating the focus rectifier filament load from the fly), and even a shorted turn or two in the focus coil can increase the focus current, but still yield good focus range. You can also eliminate the filament load from the 3A3C by using a R-3A3/ECG508 silicon replacement.

Also, make sure the B+ is the correct level - today's higher line voltages increase all the voltages in vintage sets. A dropping resistor add (complicated) or running on a variac (easiest - set it for 110 VAC and you should be good) are suggested as fixes.

Cheers,

Ah okay. Hopefully Tom sees this before he gets my CTC16 too far back together. I'd like to be able to use it and not worry about the flyback catching it self on fire.

...250 ma?:eek: When we sold those sets new, 210 ma was the absolute limit for any hope of making it through warranty without killing the 6JE6.

200-205 ma was just about optimal.
The factory manual tells you to adjust to the dip, then raise the current off-dip a bit. But that's nuts. It doesn't state any rationale for raising it. So just set it to the dip, period.

I always followed the proceedure in the service manual regarding raising the current to slightly above dip.
Of coarse, if the fly failed, they had one on the shelf, at your distributor.
I went strickly with Thordarson later in the game.
BTW, did all you seasoned techs, check the efficiency coil with every 6JE6 replacement. I'm guilty for not! :nono:

In the shop, yes, with a Pomona adapter and Simpson 260. But in the field and on the clock, it wasn't always practical to do so. But we did carry a couple of 'magic light bulbs' consisting of a #44 bulb adapter to put in the plate cap lead, to visually dip the eff.coil. One was for small top caps (6JE6 etc.), the other for big top caps (6JS6 etc.).
With a little practice, it was easy to gauge the current from the 'orangeness' of the bulb's glow.

...

The CTC16 sets lack the line adjust switch - hence the variac. Nick (miniman82) runs all of his sets on a variac - I have a Sola conditioner that brings my high line voltage down, but only to my bench, so I use my VIZ Variable (metered) Isotap to bring it down for my CTC16 when I want to operate it.

As to the cathode current, 250mA is the absolute max, and no, I've never seen one run that high. At 110V, my CTC16 runs right at 200 - I remived the focus rectifier current from the flyback load, and will probably do the same for the 3A3, all in keeping the fly healthy.

Given the dearth of available flys for pre-CTC38 sets, there ought to be a "flyback health manual" we could create - lots of sets turning up that can be restored with the existing fly, and threads like this illustrate the need. Zeno, OldCoot, miniman82, andy - could all contribute greatly.

Ah, the old 44 bulb test - I saw another shop using one of those testers - had to have some dim lighting to use it, but it worked well. Eby made the one I have. As to the Pomona adapter, I have several, and one homemade one my dad used for years. I use a center-zero "save the flyback" meter - it doesn't care about polarity - just dip to the center...

If present, the two tap points are on a terminal strip under the chassis, just under the power xfmr. Sets with the tap came wired for 'low' line voltage, and needed to be set for 'high'. It was SOP after uncrating.

The raising above the dip is to bring the sweep into a linear region of the sweep - just watch the CRT with a cross-hatch and look for any non-linearity in the picture. If any, raise the dip. I've always gone for the dip, and never had a non-linear horizontal sweep after dipping. I have seen weak 6JE6's cause linearity problems.

We had a similar procedure in the world of Avionics - dipping current in driver and output tubes in VHF and UHF radios and one '50s TACAN unit. What fun - blade tracking and turn-loc coils, all one handed operation, as there was -900 volts on some coils.....

Same here.

The HOT lamp was an RCA accesory, but IIRC it was a #39 lamp. The lamp got smashed in the bottom of the tube caddy and I had to order a box of them. Not a real common type. A small cap for the 6KM6 and a large cap for the 6JE6 et al. :scratch2:

Ours were homemade. Used #44 bulb since it's rated 250ma., just the right current range. Not sure what the #39 is rated.
On a side note, when using a milliameter in the cathode leg (an analog meter that is), it's not necessary to put a cap across the meter, contrary to popular belief.
If trying to use a digital meter for K current, all bets are off. Digitals tend to go nuts on spikey or complex waveforms, and the reading ain't to be trusted, cap or no cap.

Digital meters have their place, but not for certain applications. They take too long to make up their mind, when instant readings have to be taken.