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.

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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.

These are probably the most important things you can do before you get
into modifying the circuit design.... But what if you wanted more protection?

Electrically transformers are made up of a pure inductance component and a
resistive component, It's the resistive component that ends up getting hot.
It's the inefficient part of the wire we can't do anything about inside the
flyback....

I'm wondering, If you wanted to shave an extra 20ma. off the current running
through the flyback, could ya do it be adding possibly 2 - 10 Ohm, @ 10 to 20
watt wire wound resistor to the horizontal output cathode circuit, and
possibly shift some of that heat to the resistor and away from the transformer....?

Anyone with one of these sets on the bench willing to test it ? Naturally,
you would have to be sure it didn't cause any width problems... Etc....

Not sure if it should be in the cathode circuit, or on the business winding
on the flyback supply, probably not too smart to put in in there on the plate
cap end.... Maybe on the other side of that..... I don't have a schematic
for that set, so can't come up with the exact point.....

Anyway, my thinking is, if the resistive component in the flyback "primary"
is say 20 Ohms, and you add a 5 Ohm resistor, will you shift enough heat
off the transformer to have it not melt the wax....? And still not effect
the rest of the set materially.....?

.

I was also thinking of putting a small computer fan on the top of the HV cage in my 1954 CTC2B, 21CT55 21 inch color. I don't see where it would cause any harm. Yes, I have always thought that around 210 ma was about the max that the cathode current should be at. The HV cage on that old set is completely enclosed except for a hole in the top with a "chimney cap", in which I could install a fan. Possibly the reason that HV cages as so tightly enclosed it to reduce x-radiation.

No effect at all. Think about it, when you put a milliammeter in the circuit to check the current, you are adding the DC resistance of the meter, which is several hundred ohms, and you still have 200 mA in the circuit.

I don't think this is true at all.... Resistance of 1 - 4 Ohms max,
Several Hundred Ohms and you strongly change what the meter is actually
reading. Most good meter movements are Micro-Ampers full scale, so reading
200Ma, the current handling resistor should be pretty small.

For a current reading meter to be highest in accuracy, it would have to present
as close to zero resistance to the circuit as possible..... Just as in measuring
voltage, the meter should present as close as possible to infinite resistance
as possible to the circuit.... That is why VTVM's and digital's are choice for
a lot of really accurate DC voltage use especially, because of high resistance
on input...

.

Odd, because RCA, Jack Darr, and Carl Babcoke all call for a .22uF (RCA) or .47uF (Darr and Babcoke) capacitor in parallel to the meter.

http://www.americanradiohistory.com/...-Page-0084.pdf

What is your rationale? I know theirs - to prevent the inductive load of the meter from becoming resonant - hence, they shunt it with a bypass cap to ground, effectively eliminating the possibility. My Save the Flyback tester has a .47uf/600V across the meter

Your #39 lamp tester was in a May, 1970 Radio Electronics article - they show how to build an efficiency tester, using the #39 bulb. My EBY tester used a #44, and was able to forgo the odd lamp.

If it's a good meter - the movement is far removed from the circuit, but the cap
is most likely insurance so no sharp spike makes it to the movement....
A spike that may occur if one lead is accidentally lifted while the tv is on....
It's unlikely the movement's inductance comes into play as it is bypassed by a
resistor of small value, 1 -2 Ohms, and then further hidden in a series resistor network....

But I can see that the possibility of the high frequency and unknown internal
components to the meter could cause resonance and effect the accuracy of the
reading.... So Yes I can agree on the resonance possibility....

.

Rationale for needing no cap would be- the actual DC resistance of the instrument (e.g. Simpson 260) is very low when measuring current. The higher the current range, the lower the resistance as lower and lower shunt values are switched in. The instrument is functionally a dead short when measuring current.
So having a cap across it is fine as a 'feel good' measure, but no actual need for it.

The movement is gonna 'see' raw, unfiltered spikey waveforms anyway when the instrument is measuring voltage, and is none the worse off for it.

A little cooling can't hurt, if you don't mind the noise. I tried a little fan inside the back of my Predicta barberpole set, but quickly took it out because the noise bugged me.

Also, air carries dust, so the more air you force through an interior, the more dirt that may accumulate. I remember cleaning out old desktop computers that were plugged almost solid with dust bunnies. Those computers probably ran for more hours per day than the typical color roundie, however.

Phil Nelson

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OK I am confused. What else is new. Are there two threads on this ctc 16? Did Tom replace the power supply electrolytic caps? If not I would start there. A quick check would be to hook up a dvd to the set. Put it on pause and see if there is a slight wave in the picture. If you want to use the set as every day watcher, They should be replaced any way. The fly will get hot with the 3a3 sitting on top of it but you should not see wax dripping out of it. Your test pattern is really cool. Must make it a lot easier to do convergence

I did add a small fan to the HV cage on my CT55 and it made a huge difference in keeping the fan cool to the touch. I was also concerned about the noise, but I found a small low noise 2.25" fan at Mouser. Look for a fan with low noise and low air volume. I made a round hole in the side of the HV cage and connected it to the switched side of the incomming AC. You can hear it a bit at start up when the sound is not on but when the audio is at normal room volume it can not be heard at all.

The original flyback got wiped out shortly after the set was restored, and I did not want to chance that the UBER RARE replacement would get fried. So I added the fan and the flyback runs cool to the touch now.

It is running slightly less than 200mA, on the 6LQ6. I have not checked parts in the horizontal osc/drive system (aside from the 6CG7 which is quite strong) or the waveform. Don't know if my boost rect is silicon or what, I'd have to check that.....If it ain't then the only way I can put a 'fast' diode in is if I happen to have one in the parts I've scrapped off BPC sets. I don't stock any other new diodes that can take the voltage and current, and I don't buy parts online. I don't have any SS 3A3 or 2AV2 substitutes either.

AC at the outlet the set plugs into here with it on is 117VAC. I will look for a high line voltage primary tap on the transformer.

My thoughts on adding a fan are that one should add a Heppa filter in the air intake to limit dust intake.

The flyback was getting really really hot even before he changed out the diodes. Even before the set was working even half way correct, the fly kept getting really hot on me.

I use thermal joint compound or grease to aid in heat transfer from transformer frame to TV chassis.