UPDATE, November 24, 2024
Greetings Marshall. I started looking at the CTC5 again this evening and I will be attacking the H.V. regulation modifications next. The plan is to install a H.V. adjustment control in place of the Matrix Balance control which is located right next to the 6BK4 regulator tube socket. The Matrix Balance control never worked on any CTC5 that I have ever worked on. Every chassis that followed the CTC5 did away with it and replaced it with 470 ohm resistors at the cathodes of the demodulator tubes, and that is what I will do here. The pictures attached are as follows.
Pix 1 The parts that came out of the AGC, SYNC, Audio I.F. board from the last update. I missed sending it at that time.
Pix 2 is the 6BK4 Shunt Regulator socket. Notice the control on the right side with a yellow and blue wire. That is the Matrix Balance control that I will remove. In place of it will go a 10 megohm pot that will allow control of the H.V. regulator. I have already disconnected those wires on the other end where they connected to the demod tubes. Since this modification causes changes in the Chroma circuits, I will be doing the component replacements in that section next instead of moving to the Vertical sweep section. I did a random "in circuit" check of resistors in the Chroma section and there are a number of resistors that are out of tolerance by over 20%. So, that will be a slow task since it is all hand wired. One more note. The H.V. as measured at this point in time before mods is 17 KV. I hope to be able to adjust between 19KV and 22KV if all goes well.
More to come, Stay tuned!
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https://visions4netjournal.com/wp-co...SC03197-1.jpeg
Good evening. I have made some progress over the past few days. The H.V. Regulator circuit has been modified. A H.V. control now exists and the H.V. can be varied from 16 K.V. to 23 K.V. I have also decided to eliminate the 5U4 Rectifier tubes in the power supply and replace them with a plug in solid state replacement of silicon rectifiers that are rated at 1000 PRV at 2.5 amps. These plug in replacements can be purchased, but I make my own from old dead 5U4 tubes. I break away the glass and save the sockets and install the 1N2007 rectifiers into the socket which makes it plug in directly to the where the tubes were. These rectifiers take the place of both 5U4 tubes for power handling capabilities. The improvement is power B+ stability throughout the chassis and it saves 6 amps of current not being handled by the power transformer to power the filaments of the 5U4s. Since the solid state rectifiers are more efficient, the B+ increases by around 30 volts so I installed a 70 ohm 50 watt resistor (chassis mount type for heat control), to the top of the chassis where the 5U4's were. Now, on to the Chroma circuits. First thing I noticed is a very badly charred terminal strip where a 10 watt resistor mounts. I remembered this from my own set and it is weak spot that needs to be addressed. The charred terminal strip eventually turns in to conductive carbon and if it doesn't disintegrate first, it can actually cause a small fire. This is a very delicate piece of surgery and the 10 watt resistor that caused this damage will be re-mounted to the top of the chassis where it can dissipate its heat away from the chroma circuits. Very bad design on the part of RCA in my opinion. Basically it is a 10 watt resistor in a 15 watt circuit. I have also installed a 5 amp pigtail fuse in line with the power transformer primary. That should have been done by RCA in the beginning.
Pix. 1 H.V. reg 6BK4 socket before mod.
Pix. 2 H.V. reg 6BK4 socket after mod with H.V. adjustment added
Pix. 3 H.V. adjustment set for 16KV
Pix. 4 H.V. adjustment set for 23KV
Pix 5 5U4 tubes with solid state replacement at the bottom of the pix.
Pix. 6 Chroma circuit with charred terminal strip. Hard to see from the pix.
I will send pixs in 3 separate emails. I hope it goes well.
cheers, Mike
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The chroma terminal strip will be a very slow and delicate piece of surgery. Lots of wire and re-locating of parts to get the heat away from the chroma circuits.
Cheers, Mike