[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?