View Full Version : CTC-2B Ballast


miniman82
11-07-2016, 01:07 AM
I have a spare 2B chassis, but it was missing the ballast. I was able to locate one, but the resistive elements inside have gone open circuit so now I have to make a decision.

Do I:

A. Try to find some resistive wire and make original style elements for the inside and 'restuff' it so to speak?

Or

B. Tack some high wattage sand resistors inside the low voltage cage, and leave the empty ballast tube for visual purposes only?

If I go route A it could be tough trying to cram enough wire inside, the original elements were very fine wire wrapped around a (asbestos? Fiberglass? Silica?) core, sheathed in more fire retardant material. Probably be really hard to duplicate anyway. If I go route B that obviously works for this chassis here, but the ballast is electrically pointless then and can't be swapped into another chassis for troubleshooting.

It may even be possible to cram sand resistors inside the old ballast can, but I don't know what wattage to use since none of the schematics I have tell me how much current the ballast has to deal with.

What do you guys think?

kvflyer
11-07-2016, 09:59 AM
If the ballast is like the ones that I have seen, they are wrapped around a slice of mica; not hazardous. But... the wire is nichrome and you can't solder it, it has to be crimped. Maybe tne open is at the connection in the ballast?

Electronic M
11-07-2016, 10:42 AM
It may even be possible to cram sand resistors inside the old ballast can, but I don't know what wattage to use since none of the schematics I have tell me how much current the ballast has to deal with.


That is easy to deal with. Assuming the ballast uses a standard (presumably octal) tube base/socket just get another base socket pair of that type, and if your other chassis has a good ballast make a socket extender/breakout adapter with the extra base/socket pair to allow you to insert a current meter in series with each resistor such that you don't have to disturb the original wiring.

dieseljeep
11-07-2016, 11:28 AM
That is easy to deal with. Assuming the ballast uses a standard (presumably octal) tube base/socket just get another base socket pair of that type, and if your other chassis has a good ballast make a socket extender/breakout adapter with the extra base/socket pair to allow you to insert a current meter in series with each resistor such that you don't have to disturb the original wiring.
IIRC, it's not used as anything but a surge limiter. It depends on where in the circuit it is used.
Never have worked on one, I only seen one close up at Nick's place. :thmbsp:

dieseljeep
11-07-2016, 12:04 PM
IIRC, it's not used as anything but a surge limiter. It depends on where in the circuit it is used.
Never have worked on one, I only seen one close up at Nick's place. :thmbsp:

I just remembered I have the Riders vol 13 coverage on CD rom. Thanks Jim Menning!
I appears to me, that it's a voltage divider for the IF strip and the field neutralizing circuit. I don't have a schematic for the CTC2B. This info is for the 15" set.
Two twenty watt resisters should fit inside the can.

StellarTV
11-07-2016, 12:14 PM
Some of the elements in Motorola ballasts have been successfully replaced with non-polarized electrolytic capacitors. 10uF works to replace the resistive line cord in 30s era radios. You can probably find a similar solution and save a resistor or two.

jr_tech
11-07-2016, 12:44 PM
Calculating from the voltage drops involved (400 to 285 V) with some guesswork for amount of current drawn by the vertical centering circuit, it would appear that both the 500 ohm and 430 ohm resistors should be at least 26 watts rating.
The capacitor trick won't work here as this is strictly a DC circuit.

jr

TV'S&MORE
11-07-2016, 03:22 PM
Service literature shows 315 ohms between pins 1 and 3 800 ohms between pins 1 and 2 My ballast measure's 310 and 830

jr_tech
11-07-2016, 03:55 PM
Interesting... my RCA field service guide (1955-1966 color) shows that R-101 (between pin 1 &2) in the ballast is 800 ohms (I mis-read as 500 ohms) but R-102 (between pin 1 &3) is shown as 430 ohms. There is also a jumper shown between pin 5 &7.
Recalculating for 800 ohms I get about 17 Watts for R-101.

jr

miniman82
11-07-2016, 03:56 PM
If the ballast is like the ones that I have seen, they are wrapped around a slice of mica; not hazardous. But... the wire is nichrome and you can't solder it, it has to be crimped. Maybe tne open is at the connection in the ballast?


I was hoping for that, would have made an easy repair. Both elements were open somewhere near the middle, meaning I have to start over from the beginning.

BTW, you're only an hour from me in Great Mills- stop by sometime. :smoke:


So looks like the only viable option here is probably mounting some big sand resistors in the LV cage then? I hate doing that, but this chassis is already a little hacked I suppose. Had a 6JE6 in it for H-sweep when I got it. lol

WISCOJIM
11-08-2016, 12:21 AM
I just remembered I have the Riders vol 13 coverage on CD rom. Thanks Jim Menning!
You're welcome. BTW, feel free to make and share copies of those to anyone who wants them.

.

Electronic M
11-08-2016, 09:13 AM
IIRC, it's not used as anything but a surge limiter. It depends on where in the circuit it is used.
Never have worked on one, I only seen one close up at Nick's place. :thmbsp:

I think the ETF has the CTC2B/21CT55 service lit in their color technical info page (along with every other RCA roundy).:thmbsp:

dieseljeep
11-08-2016, 10:29 AM
I think the ETF has the CTC2B/21CT55 service lit in their color technical info page (along with every other RCA roundy).:thmbsp:

I had a touch of the flu yesterday and things didn't register as well. I never thought of looking there.

Electronic M
11-08-2016, 11:43 AM
I had a touch of the flu yesterday and things didn't register as well. I never thought of looking there.
Yikes. Hope you get well soon.

dieseljeep
11-08-2016, 01:59 PM
Yikes. Hope you get well soon.
Thanks! A little better today.
BTW It was great meeting your Mother at the radio meet. :thmbsp:

wa2ise
11-08-2016, 04:01 PM
If the heater string adds up to around 84V, you can use a rectifier diode, without any filter cap, to effectively drop the 120VAC line. This saves the energy that would be wasted as heat. Remember, it's power = volts squared over resistance. The diode cuts the power in half, and the effective voltage is 120V times the square root of 2 (from the half) which then = 84V.

Electronic M
11-08-2016, 04:53 PM
If the heater string adds up to around 84V, you can use a rectifier diode, without any filter cap, to effectively drop the 120VAC line. This saves the energy that would be wasted as heat. Remember, it's power = volts squared over resistance. The diode cuts the power in half, and the effective voltage is 120V times the square root of 2 (from the half) which then = 84V.

You missed the part where it is mentioned that the Ballast in the CTC2B (a parallel heater transformer powered set) is used as a DC B+ divider....It has to remain a resistance based divider....Unless of course nick wants to go with LM317 DC to DC regulators. For the drop he'd need at least 4 in series (I've ran those chips in series as well as parallel before) to safely drop 115V (each device can only drop 40V max between input and output terminals). The biggest hurdle of using the LM317 is what to use as a ground reference...You might be able to keep the 430 ohm and reference the whole shebang to the centering terminal (thus replacing only the 800 ohm with LM317s), but if you want to eliminate all resistors you would need a ground reference.

wa2ise
11-09-2016, 03:34 PM
You missed the part where it is mentioned that the Ballast in the CTC2B (a parallel heater transformer powered set) is used as a DC B+ divider....It has to remain a resistance based divider....Unless of course nick wants to go with LM317 DC to DC regulators. For the drop he'd need at least 4 in series ...

The LM317 is a linear voltage regulator, in which case the voltage drop produces waste heat anyway. So you might as well use power resistors. If you have DC-DC converters (essentially a switching power supply) that might work, if there's no RFI from the switcher. But if you want to keep the set as close to the technology of its day, the resistors would be the way to go.

Some TV sets used the audio output tube as a voltage dropper for the set's IF strip.

walterbeers
11-11-2016, 08:14 PM
The Ballast in my 21CT55 was good, (other than being rusty), measuring very close to the 800 and 430 Ohms. Actually it's just 2 high wattage resistors inside of a plug in unit, with a jumper between a couple of pins. If you can I'd just see if you could find a couple of 20-25 watt resistors and put them inside of the ballast, although I suppose space could be a problem. I painted mine with high temp silver paint for appearance.