Penthode, your work is impressive. Please keep us up to date with all your accomplishments.

I do have a question. Why do mice like old TVs? Is there some food source such as cotton covering on old wires that attracts them? It's surely not warmth as these old TVs are not being turned on everyday. Could it be as simple as a place to bed down for the night?

just a place to hide?

To hide yes because under the CT-100 it was pretty secluded. The previous owner obligingly left the cover off and the mice stuffed the underneath with tons of cotton which made it pretty cosy. I think the set was in a non temperature controlled environment from the look of it.

The problem is the mice appear untidy creatures as the unine soaked cotton against the steel chassis leads to pretty extensive corrosion. I would normally pass on a set in this condition but as this set is special and the CRT appers to have miraculously survived, the thorough overhaul of the affected region is justified. The aim will be to put it back together closely as possible the way it left the factory. With new capacitors, of course.

The rivets are scheduled to arrive on Monday which means I can begin rewiring the chassis once the tube sockets are back in place. I removed most of the IF strip as a loom only removing what was necessary to pull the assembly away. After a thorough wash, iit will be put back in place and connected,

Many of the components are salvagable after a wash. Many resistor leads and disc bypass capacitor leads were badly corroded. The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs. I found a bag of old style ceramic disc 820pf on ebay and will use those as necessary. And the badly corroded carbon composition resistors will be replaced with identical looking carbon composition units.

"The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs."

I looked ... both Mouser and Digikey have totally suitable, totally ordinary disk ceramic
caps. Both have over 40,000 in stock! I used these in my CT-100 (various values) and
they work and look just fine, albeit some are blue.

Can you show me the link? I looked and the 820pf ceramics bore no resemblance to the original. I have previously used Newark, Digikey and Mouser for years.

The NOS I bought from eBay looks a very close match.

Mouser part numbers 594-S821K29X7RN63L6R or
75-562R10TST82 They have 19,047 of the top one in stock!

If you want NP0 there is 81-RDE5C3A821J2K1H3B but they are blue.

I tend not to trust most capacitors, resistors, found on eBay anymore, and especially transistors :(
just too many fake parts.

I agree wrt ebay and transistors. I have been burnt a few times. However if the seller is in the US with what appears to be NOS vintage resistors and ceramic capacitors I have had no problems. When wanting to keep the original appearance I have patently searched for just the right part.

It must be just me. I even baulk at newer metal film resistors which do not match the older carbon composition resistors in older vintage equipment. For 1930's sets, I have a store of older dog-bone style resistors.

I used to restuff paper capacitor but do not bother anymore and certainly the gleam of an epoxy dipped capacitor does not look too out of place. I will use modern film capacitors of a higher breakdown voltage in order to ensure the component is of a physical size roughly equivalent or only slightly smaller than the original.I will always restuff electrolytics though.

Which reminds me, I have a question on capacitors used in 50's set vertical sweep circuits minus the blocking oscillator transformer. I have found that it appears the capacitors are critical in that proper capacitor characteristic choice is essential for maintaining good sweep linearity during warmup over a half hour or so. Has anyone else had this problem?

Been cleaning the considerable gunge off the chassis this week. Removed the high voltage compartment and the selenium rectifier frame to give it a thorough clean. Started replacing paper capacitors in the HV cage and now that it is clean have given it a thorough inspection.

Whilst making checks around the selenium rectifier, found a fuse blown and a jumper wire which had been placed across it. Not good. Then the resistive ballast if that is what it is called I examined and found part of it open. Closer examination revealed it appears to be simply a voltage dropped with an 800 ohm and a 300 ohm resistances to each drop the 400v DC supply to 285v. 115v across the 300 ohms dissipates 41 watts and 800 ohms 16 watts. The 300 ohm section is the one open.

It looks to me a bit of a bad design wasting 56 watts like this. That is a good chunk of the total 475 watts the setg consumes. I guess power was cheap in those days!

Anyhow think what can I do to salvage this? I found a 50 watt 330 ohm and 25 watt 820 wire wound chassis mount resistors back to back will just fit the 30cm diameter ballast container. But that is a lot of power to dissipate.

Has anyone else dealt with this or have any ideas?

Personally I'd rather stay true to the original design despite the 56 watts of heat given the rarety of replacement parts in the chain. An open resistor is far cheaper than a smoked transformer or buckled plate when a redesign goes haywire. Just my two sense

In my CT-100 I stared at the low voltage cage for days before deciding what to do.
I love the look of those huge orange selenium rectifiers.

But I also noted that the chassis mount can electrolytics were soldered down.
I decided that unsoldering all of them would be dangerous. Cutting them
all off near the base to restuff would be difficult and risky too.

So I decided to rebuild the whole B+ power supply with modern caps, 5 watt
silicon diodes, several fuses in various places, and large old-style Ohmite series 210
tapped (adjustable) resistors to drop voltages. In my
case the original ballast was OK and was left in series with the new Ohmites.

It put all those on an epoxy circuit board and mounted it in the cage.
I used the usual chassis clips to space the resistors at various distances from the board.

I set the line voltage with a Sola regulator transformer and a Variac ( permanently
mounted ... I inherited about 50 Variacs from a scrapped chem teaching lab)
so the filaments were exactly 6.3 and then adjusted the resistors so that the various
B+ voltages were exactly as Sams specified.

The fuses saved the 15GP22 from its first two arcs, as it got gassier and
gassier. But the third one, while it did blow the fuse, was fatal.

Have you ohmed out the vertical convergence transformer for shorts and opens yet? IIRC the original transformers were painted black while the modern reproductions were silver in color. You might have gotten lucky and have a reproduction.

I forget what the case was on my CT-100 (I think the previous owner addressed the power supply when they did a janky amateurish recap), but my 21CT55 (CT-100 factory modified to drive a 21AXP22) both ballast sections were open so I bought a couple of chassis mount high power resistors off mouser and found places on the rear upright where the resistor screw holes lined up with the cage screw holes. I gutted the original ballast and it now exists purely as decoration.

I also ended up replacing each selenium with 12 modern silicon diodes in series to emulate the original selenium voltage drop.

It was a very good thing you replaced the selenium rectifiers with modern silicons, as seleniums can short and give off a very unpleasant-smelling gas when they fail.

I did not realize, however, that you needed to replace the selenium rectifiers with 12 silicon diodes, for a total of 24 silicons. I am thinking your TV used two selenium rectifiers, as a lot of 1950s TVs did; my folks' second TV, a Crosley Super V from about 1955, had two seleniums in the LV power supply. (Their first television, a 1954 RCA Victor 21" console, had a 5U4 LV rectifier, IIRC.) These selenium rectifiers, IIRC, were still good when we finally put the Crosley Super V in the basement in 1965 (where it, and the cabinet of the 1954 RCA, remained until 1972; long story and OT), replacing it with a Sears Silvertone all-channel 17-inch b&w portable shortly thereafter (at my mother's insistence, as she wanted an all-channel TV by this time; the reasons for that are OT for this thread).

Now that your TV has silicon LV rectifier diodes to replace those seleniums, you won't have any more trouble with the rectifiers for a long time unless they short again, giving you one less thing to be concerned about. However, this shouldn't be an issue; if the rectifier diodes short again, the TV's line fuse(s) or circuit breaker, of course, will open immediately, so you will know beyond the shadow of even the most unreasonable doubt that there is something wrong in the power supply.

I never understood why selenium rectifiers caught on - they seemed to be a headache, even then. Was the filiment requirements for two 5U4s that much?

With the 5U4 filaments at 3 amps per tube, I'll bet saving 6 amps with the selenium rectifiers made for an easier life for the power transformer :thmbsp:

I have stared at this set's power supply and haven't decided anything yet. I would like to keep it original especially if the selenium rectifier are good. I have generally had no problem with the seleniums unless there was a B plus short. But the fuses are there for protection.

I was thinking of fitting a 50W wirewound resistor in the ballast tube. But 41watts? I wonder if the resistor would survive? Maybe remove the seleniums and use the space to mount some old style porcelain 100w Ohmites?

Yes that was one of the first thing I did. I lifted the secondary and did not see the VTVM needle quiver which suggests the leakage resistance is greater than 1000 Mohms.

Only received the rivets for the tube socket remounting yesterday. The rivets are 3/32" x 1/4" and the 1/4" length was needed for the phenolic wafer socket + tube shield bracket + chassis thickness. Had to drill each rivet core by an additional 1/32" and reduce the diameter of rivet head from 0.200" to 0.150 to match the original over heads.

Supported the front chassis section with books and a punch was clamped in a vice below the chassis for the head of the rivet to rest. Then used the hammer and rivet tool on the topside to spread the rivets. Two sharp taps and a couple of finishing tops to ensure the tube socket is firmly secured.

The tube sockets are back in place and along with the IF and Audio Ratio Detector transformers. Currently replacing the potentiometers and soon will commence rewiring.

So much cleaning to get rid of the mess left by the previous tenants. Looking much cleaner now. And in case you forgot how bad it actually was, go back to page two of this thread to have a look!

This week's update: I have completed the reinstallation of the video and sound IF and audio amplifier wiring to the previously mouse encrusted region. I am awaiting a couple of capacitors and that's it. I shall reattach the front section of the chassis next week and reintegrate the two. I reckon it has taken about 60 solid hours of effort to get this far.

All of the resistors in the mouse infested area are new as are the capacitors. I reused the pots after dismantling and cleaning. All of the resistors are NOS old style brown body resistors.

The high voltage box which was removed has been cleaned and all capacitors (apart from the doorknobs) have been replaced.

Have been meticulously following the dozens of photographs taken from different angles as well as refering to the schematic to confirm connections. I took copious notes when dismantling but have hardly needed to refer to them.

Still have to finish replacing the paper dielectric capacitors on the front section and a large bunch on the main chassis.

Beautiful!

What percentage of the work would you say has been done towards first light?

What percentage? I feel I am almost to the point where the real restoration may begin. Re instituting the removed chassis section will take another full day to do it properly. And then replacing all the paper capacitors and tidying up previous repairs. The power supply needs work: what to do with the ballast resistor And all the filter electrolytics. RCA used excellent quality electrolytics in the late 40's and early 50's so I will be curious how the CT-100 filters will be. And there is refinishing the cabinet while the weather is good.

I would like to think I have nearly reached the 50% point before the first power.

I have learned a lot about the curious nature of the CTC2 chassis design. It does not feel like a big run chassis from a number of little anomalies I have found such as component placement. Certainly with the high number of power resistors, at 475w it is not a power efficient design.

In the day when an uninsulated home was heated with electric resistance another 475 watts was not a big concern

Getting the subchassis's prepared for putting them back together. And scrupulously going over connections and components.

I make ote of the Peter Deksnis alert for the 6BK4 HV Regulator replacement for the 6BD4. As he discovered, pin 8 on the tube socket is used as a tie point for the original 6BD4 circuit. Substituting the later 6BK4, it has a pin 8 interconnection to the cathode.

https://www.earlytelevision.org/Deks..._6bd4-6bk4.htm

I added a tag strip wiring point to carry the connection away from pin 8 of the tube socket as,depicted below. After this last item, I recounted the HV cage back to the main chassis.

The CRT socket HV leads for the electrostatic focus and convergence electrodes had deteriorated and,were,about to fall off. I missed out on the one recently for sale on eBay. Taking the socket apart, revealed the HV electrodes encapsulated in a molded plastic piece. I had to break the plastic surround to remake the connection and in the process of making a small plastic surround replacement.

The vertical integrator leads were corroded from my mouse friends to the point one lead easily disintegrate and dropped off. For those familiar with these things, it is a Central "Couplate" number PC-101. I decided to remanufactured one as it has only a few passive components: a 002uF, two .005uF and 22k and 8.2k resistors. I ordered from Digikey some surface mount chip components I will put on a little board less than the size of the original couplate.

I assembled my replacement for the PC-101 couplate this evening. Parts cost about $1. Cheaper than the Centralab unit.

Surface mount resistors and capacitors on a scrap board. The 0.01uF cap is a small ceramic disc mounted on the rear.

Making more progress on the CT100. The reunited wiring is complete! Spent over a dozen hours reuniting the HV cage and the front section including the IF amplifiers to the main chassis. Laboriously checking photographs, my notes and the schematics (as there are variations) finding where the approximately 35 wire and components originally went. The photos help ascertain the original lead dress.

Some of the original wiring looked messy. I tried to clean up some of the worst congestion but ensured, especially around the IF sections I had to fully remove, that it was as close as possible to the original layout.

Next comes the replacement of the remaining paper capacitors. I tested a few and the leakage is incredible. It only goes to prove that plugging in any set of this vintage or older without addressing the paper caps is crazy.

As for the electrolytics, I aim to see if they will reform with low leakage. It will be easy to weed them out and if there is any doubt, out they go.

Here are some photos where this CT100 is now. Note the lower right which was previously the mouse abode.

Great!

Glad to see you recognize the importance of routing to proper function and are avoiding changes for the sake of visual neatness in the high frequency areas. You probably also know that routing and grounding points can affect the coupling of sweep currents (horizontal ringing "jail bars") into the video, but thought I'd mention it here for others who may be newer in the hobby.

Been going through the chassis this evening. Every one of the white blob peaking coils is open circuit: 180uH, 1.0mH, 1.6mH, 1.9mH and 3.6mH. The biggest ones are in the I and Q chroma channels.

I have an NOS Meissner 180uH replacement. But it is difficult sourcing the others. Anyone know a good source of supply?

I found on Amazon a spool of 44 AWG magnet wire and may end up winding them myself. Easy to measure the inductance but achieving the correct Q may be a bit of a challenge.

As to peaking coils: don't try to find NOS ones. Just get the small to medium
size (size of old fashioned 1/2 or 1 watt carbon resistors) cylinderical axial
ones from Bourns or API Delavan. Get shielded if they have them. Make sure
the self resonance frequency is high enough.

I do very strongly recommend that you don't use the approx 6 mH specced
for the Q channel ... it seriously ruins the chroma reaponse. Get one that's in the 2.7 or 3.3 mH range.

They don't look right but work very well. You may need to search both Mouser and Digikey to find all values.

The picture on my CT-100 is the best recommendation for these.

The coil's Q is not a problem, all of those coils are plenty good enough because they
have ferrite forms. The shielded ones also have ferrite outer shields.

Peaking coils
 

I was able to get an assortment of peaking coils quite reasonably from Moyer electronics in PA to solve the same problem I had with my Hallicrafters set.

That is good to know. I will check it out. Thanks.

After thinking about this a bit, I believe the large inductance was to specifically limit the Q bandwidth to roll off at 500kHz. The I channel is 1.5 MHz wide.

Remember the I and Q are transmitted vestigial sideband in quadrature which means extending the Q bandwidth will lead to quadrature crosstalk. Further in this early design both Y and I channels have delay inserted to align with the limited bandwidth Q channel: Y a larger delay than I. Reducing the peaking coil inductance will extend the Q bandwidth which will reduce the delay.

All sets I believe following the 21CT55 used equa-band narrow channel (500kHz) chroma demodulation apart from my CTC5 Deluxe which has a equa-wide-band chroma demodulator. This means the CTC5 Deluxe intentionally introduced quadrature crosstalk in what appears to be an attempt to increase marginally chroma resolution. The crosstalk is noticeable at abrupt color transitions. (There was a 1955-56 RCA review I recall reading about this many decades ago. I need to look for it).

So I am going to investigate this further. Certainly I can do some tests with the peaking in circuit resonance with the technique outlined in my Measurements Lab. Grid Dip Meter applications notes pertaining to video amplifier design which outlines how to determine peaking coil inductance in circuit.

I think you've got it right. Since the Q coil is large, it's resonant frequency probably is also more critical - too low and you could bite into the 500 kHz bandwidth and get ringing. Going the other way, a little quadrature distortion could be hard to see on a small screen.

Going through the chassis replacing capacitors and the odd resistor. The previous owner replaced a number of capacitors it appears years,ago with orange drop Spragues but left long leads on the replacements. Tidyi g up as I go along.

I saw a little wire jumper under the chassis I initially thought was jumping an old fuse. Found it bridged the power switch. I pull out the switch and found it quite charred. It was a Centralab switch and potentiometer so I proceeded to look though my box of old parts. Found many exact physical replacements. However I found that all the other switches fitting the control were only 3 amps and the burnt out switch was rated 5 amps. Think about it: this set dissipates 475 watts which means it must drawabout 4 amps! To avoid any physical modification to the control, with the 3 amp swich unit now married to the old CT100 control, there is space underneath to fit a 15 amp @ 115v Potter Brumfield relay.

I amazes me the power this beast consumes!

Making further progress. Hoping to within the next couple of weeks power up the chassis minus the CRT.

Replaced most of of the paper capacitors. This chassis takes a lot and awaiting an order from Digikey to complete.

Reforming the can electrolytics: all coming up with low leakage after a few hours feeding a 10mA current limited supply. It looks like this set has sat dormant for the past 40 to 50 years as all the earlier replacement capacitors are quite old themselves now. Despite that, the electrolytics came back from almost a dead short to holding full rated voltage with less than 100uA leakage in just three hours. Not bad. We will see how they fare.

The design uses early cartridge electrolytics for DC coupling in the chroma stages and despite coming back with low leakage, I am substituting new ones. The 4uF 450v units are on order from Digikey.

My power switch solution entailed installing a 120vac relay. The relay contacts are rated at 25A at 120vac. It was interesting to note the original Centralab 5A switch on the volume control physical form factor matches the standard 3A switches. I can picture in my mind RCA Victor engineers calling the Centralab engineers in around 1953 asking them to beef up the specs from 3A to 5A and the incredulous Centralab people replying "What the heck are you powering?"

Anyhow, the photo below show the fitment. The replacement 3A switch on the volume control now only has to energize the relay.

I shall be substituting 3A silicon diodes for the old Federal selenium rectifiers. And still considering various solutions for the super hot voltage dropping resistors.

The KRK12 tuner unit has been fully dismantled, cleaned and lubricated and is ready to re attach to the main chassis.

'I can picture in my mind RCA Victor engineers calling the Centralab engineers in around 1953 asking them to beef up the specs from 3A to 5A and the incredulous Centralab people replying "What the heck are you powering?" '

It's the bread/bagel switch! :D

I have been considering replacement of the Selenium rectifiers. They are connected in a full wave volage doubler arrangement. I plan to replace them with a pair of 1N5208 diodes which are rated at 3A with a peak inverse voltage of 800volts.

First I thought I should test the old Federal units to determine their current state and performance. I calculated the typical full B supply current from the schematic diagram as indicated in the photos below. The full load current appears to be 600mA and I used my adjustable low voltage bench supply to see what the forward volatage drop of the selenium rectifier is at 600mA.

I was surprised to find the drop only to be 10 volts. If I was to substitute silicon diodes and ignoring the junction drop of about 0.6 volts, the series resistance to effectively account for the diode substitution works out to be 15 ohms. Power dissipation would be 10 x 0.6 = 6 watts so I should get away with a 10 watt resistor.

I am curious as to the failure mode of selenium rectifiers. I understand the forward resistance rises with age. But 15 ohms at 600mA does not seem bad and both rectifioers have almost identical forward resistance. I suspect that the rectifiers may reach a point where the dissipated heat leads to a thermal runaway situation. Will need to do more research on this.

Not: In my forward voltage drop test, I arbitrarily used 10 ohms in series as a current limit as I brought up the voltage supply. The voltage aimed for across the series load resistance was 6 volts which woulkd man 600mA is flowing.

Dunno how true it is, but I've heard tell that reverse leakage in aging seleniums can contribute to heating. Might be urban legend though.

Logically, the power dissipated by reverse leakage would be minimal unless the selenium rectifier broke down. My understanding is that the forward resistance increases with age. And as the forward resistance increases, the power dissipation would increase. Thermal runaway would occur if the resistance increased with temperature.

I have completed the paper capacitor replacement as well as the disassembly and reassembly of the IF stages to clean out the mouse nest. Last two remaining jobs:
1) Replace/fix the open peaking coils.
2) Arrive at a solution for the dropping resistors (ballast).

Peaking coils: All of the white encapsulated coils are open. The white concrete like covering of the coils was a really bad idea. I managed to salvage two by carefully crunching off the white exterior and fishing for the coil ends. There were signs of green "vertigris" at the wire ends. I managed to find the ends and reattached. However I still need a couple of 1000uH and the 6900uH coils.

I reflected on the design and have dismissed the substitution of different coil values. The I and Q channels have predetermined bandwidths of 1.5MHz and 0.5 MHz respectively. The coils in the I and Q channels facilitate the different bandwidths hence the values must be maintained. Further, the wider I channel has a delay inserted to align the narrower Q channel so it is important to ensure the bandpasses remain as designed to minimize display chroma registration and alignment.

I am awaiting the delivery of a spool of AWG44 wire and contemplate making some coils myself. Once installed, I shall sweep I and Q channels in the course of overall alignment and testing of the chassis prior to attaching the 15GP22.

2) Ballast Resistor: I have decided to mount the 315 ohm 50W and 800 ohm 25W resistors on a heat sink assembly which will plug into the ballast socket. I decided again using the chassis itself as a heat sink and/or mounting the ballast resistors over or near the selenium rectifiers as I want to keep the heat source isolated as much as possible from the CRT bell. I am concerned the temperature source will be detrimental to the CRT.

Also note I decided against using the selenium rectifiers. I have left the rectifiers in situ disconnected and immediately below them have installed a tag strip to which is attached two 3A 800piv rectifiers and a 10 ohm 25W dropping resistor.

I shall be assembling the ballast replacement this week. The electrolytic cans all check okay and the capacitors have been reformed. I should be on target for a first power up this next weekend.