Found an RCA CTC5

[Penthode]

Originally Posted by ohohyodafarted

Try to find an early Admiral scrapped chassis from a model 30A14CC1 or similar with the separate power supply chassis. The cable that connects the power supply chassis to the main chassis on that set uses the same plug and the socket. The one on the chassis can be removed to use as the female end. This is a very common B&W set and there are probably a number of parts chassis around. Else you will need to find a CTC5 parts chassis and a CTC5 convergence yoke to obtain both the socket and the plug to make up the needed cable.

Thanks Bob.

In the meantime until I find the appropriate connectore I shall extend the CRT and yoke leads and just leave the convergence coils attached to the chassis and off the CRT until I have confirmed a sensible picture.

[Penthode]

I had a chance to work on the CTC5 today. I am methodically going through the chassis. I traced the 25Hz power supply and this is what I found.

The main chassis transformer was exchanged for a filament transformer only. The box on the chassis is indeed a transformer with 3 secondary windings: two for the 6.3v strings and 5v for the rectifiers. Note the Montreal factory substituted the unique Canadian Robertson head screws to hold the main chassis transformer.

The auxillary chassis has a whopping 20 pound transformer for the B supply only. The auxillary chassis also has a big filter choke and a pair of 80mfd 450v electrolytics which parallel with the 80mfd filters on the main chassis.

The 25Hz transformer will run cool at 60Hz and the extra filtering should make the B supply really clean.

There is evidence of the history of the set's manufacture. The date codes on the main chassis run from the 20th week of 1956 through to the 39th (the latest I could find on a component). The auxillary chassis electrolytics are dated December 1956 so the set's delivery was probably early 1957.

I was amused by the somewhat sloppy modification in one regard: some of the added connections were not soldered! The wire that attached to the rear socket for the primary of the B supply transformer was not soldered as was the B transformer lead that attached to the 5U4 rectifier plates. The connection to the 5U4 actually is burnt from arcing. I suspect the previous owner must have found the set unreliable hence it appears it was not used much. All of the receiving tubes, including the 6CB5 Horizontal Output and the 5U4 rectifiers appear original.

[mstaton]

That chassis cleaned up nice. Looks like a nice project.

[Penthode]

Some progress has been made with this set. I was lucky because this color TV receiver was not stressed or hammered during its life. Apart from a capacitor change on the vertical sweep board in 1965 (assumed from the 1964 capacitor date code and the 1965 repair tag on the HV cage) it looks as if it hasn't been touched. Oh yes, it had the contrast control mod. and from the look of it with same type paper capacitor, it was done at the same time.

I am currently reforming the electrolytics. It appears as if this set had not been powered for many years because the electrolytics were almost a dead short. By slowly reforming the dielectric, it is important to limit the current to about 5ma. Each capacitor took about 15 minutes to come up and at full rated voltage the current is about 0.1 mA. Because this is a Toronto set for 25Hz, two additional 80mfd capacitors were added to reduce the ripple. These are Canadian made Mallory electrolytics and they are taking much longer to reform. If the current does not drop below 1mA, I will be inclined to replace these.

Paper dielectric capacitor leak current and I will replace all paper capacitors which are in high impedance circuits and/or have above 20VDC across them. The larger 0.47ufd in the convergence circuit I will likely leave unless I have problems with convergence.

There was an interesting RCA modification made to the later CTC5N chassis: this involved changing the source of the plate voltage to the bandpass amp. and the plate supply to the color difference amplifiers. This was to prevent grey scale changes between color and B&W programs (color burst on vs off from the broadcaster). My set has the 10kohm dropper resistor which replaced a 6.8kohm unit. The 10kohm 10watt resistor dissipates about 8.5 watts! In the closed container chroma circuit, the heat melt the wax on the paper capacitors and burnt the insulation of wires running about half and inch away from the resistor. I plan to mount a 10k 20watt resistor outside the chroma can near the rectifiers.

I have attached the drawing of the chroma chassis highlighting the modifications RCA made on the later chassis. I have also attached the Radio College of Canada note of the Toronto 25Hz power conversion modification.

Lastly, I was curious to find that the static convergence is governed by the the DC obtained from the 6CB5 Horizontal Output cathode current. It would seem that investigating using a separate outboard DC supply would be more suitable. Would this element of the design possibly account for the frequent reports I have read about the drifting CTC5 convergence?

[Penthode]

The Canadian Mallory electrolytics (80 ufd @ 450V) eventually reformed okay. Leakage current for each eventually dropped to 0.1mA at 450v after an hour for each. These capacitors were initially reluctant to come back: at first, when only 20VDC was applied, the leakage current was already 5mA and the current initially didn't appear to drop significantly. However, as these capacitors woke up the currently dropped right down.

I am now confident all the electrolytics have reformed okay and are fine. I am grateful the previous owner did not power up the set.

I today removed the components from the neck of the 21AXP22A for cleaning and examination. After reading the previous posts about disintegrating yoke covers, I was expecting the worst. Somehow the yoke on my set survived. I simply removed the yoke, cleaned off the dust and wiped it over with a damp cloth and found no problem with it. Curious why this one has survived and others I have seen are totally shot.

[Sandy G]

The cold in the Great White North preserved it, ehh ?!? (grin)

[miniman82]

I suspect moisture has a lot to do with it. Better make a cast of that thing and get it reproduced before it falls apart!

[zenithfan1]

Interesting, the one on my Wingate is ok too. It was produced in 1956, while my CTC4 was made in '55. The 4's cover has turned to dust. Both sets were from their original homes in a similar climate. I wonder if there was a change in material somewhere in production?

[Penthode]

I have nearly replaced all the paper capacitors. I have gathered from an earlier thread that there are paper capacitors masquerading as mica look-alikes which should be changed.

I examined some of the paper capacitors for leakage and they are all bad! What is worse is when they are heated: I tried applying a little heat at the leakage increased at an alarming rate. Maybe I could use them as a temperature sensor in a thermometer. Boy, RCA must have really skimped on quality to keep the cost down!!!

I checked the electrolytics again and they have remained good apart from the additional Canadian Mallory 80mfd units for the 25Hz modification. These capacitors have become very leaky again and have lost the dielectric reforming I did a few weeks back. They will have to go... time to repack.

Going through the chassis (it is a CTC5 Deluxe) I have found an RCA factory modification which I feel was poorly executed. Mine is a "P" chassis and the later factory runs had the modification to improve grey scale between color (burst on) and black and white (burst off) programming. The plate supply for the first chroma bandpass amplifier was originally attached to the +300 vdc line through a 6.8kohm resistor dropping resistor. The modification moved the supply to the +385vdc line dropped through a 10kohm resistor. The modification meant that the power dissapation for the dropping resistor increased substantially (to 8.5 watts). This left charred insulation and components near the resistor. Because the chroma unit is enclosed, the ventilation is poor which made a bad situation worse. All the wax capacitors showed evidence of melting!

I decided to split the resistance: I installed a terminal strip near the rectifier ventilation and installed a 6.8k 10 watt resistor there. This was in series with a 3.3kohm 5 watt resistor mounted in the chroma chassis exactly where the 10kohm resistor was. The 3.3kohm resistor will dissipate now just over two watts.

Note the photo of the charred remains of the old terminal strip. I had already replaced the charred wiring. The original terminal strip was a miniature unit and I went to the trouble of modifying a larger terminal strip to fit. (I would not expect to make money on a CTC-5 anyhow).

My set otherwise looks lightly used. I would be curious to hear from others who have the earlier versus the later deluxe chassis and this issue. There must be others with this problem...

[DaveWM]

which look alike paper mica are there, I did not change any thing but the tube paper caps on mine?

[bgadow]

I had to replace a charred terminal strip/resistor, etc, in mine. I was thinking it was beneath the video board, under the removeable shield, but I might be wrong. I haven't noticed a problem with my yoke cover, either, but have plenty of other sets with that disease.

[Penthode]

Yep. I think that is the same resistor and terminal strip. The video amplifier hasn't the shield underneath but the chroma demodulator chassis does.

This is plain bad design.

[Phil Nelson]

Originally Posted by Penthode

there are paper capacitors masquerading as mica look-alikes which should be changed.

There were flat molded paper capacitors that resemble mica caps with colored dots. You can generally tell by the capacitance value whether it's paper or mica (micas usually have considerably smaller values). This article should help you tell them apart:

http://www.antiqueradio.org/recap.htm

My CTC-7 had a number of tubular paper caps, but none of the flat molded paper kind.

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

[miniman82]

I can't remember if mine had that burnt up resistor in it or not, but the chroma section was very waxy from all the caps melting.

[Penthode]

Originally Posted by miniman82

I can't remember if mine had that burnt up resistor in it or not, but the chroma section was very waxy from all the caps melting.

I believe you'd be referring to your Wingate? It would depend whether it was the early or later chassis.

The melted capacitors certainly sounds like it.

I also checked the 2watt resistors nearby. The 22k (10%) measured 33k and the 82k (10%) measured 96k. They were right next to the resistor dissipating 8.5 watts. These are well out of tolerance and I am beginning to suspect a lot of the other resistors have drifted as well...