Alrighty. Let's get this started.
First some background. RCA did a number of field trials starting way back in 1931 to test the feasibility of commercial television service.
These first sets were only 120 lines. Only 16 were made and at least one still exists. AM modulation for both audio and video with wide carrier spacing. No sideband suppression. Small experimental CRTs with green phosphor were used.

Much more info in TELEVISION Collected Addresses and Papers on the Future of the New Art and Its Recent Technical Development Volume 1 (https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/RCA-Books/RCA-Television-I.pdf). Published by RCA INSTITUTES TECHNICAL PRESS.

https://live.staticflickr.com/65535/54991349727_3bbecdd9c5_z.jpg (https://flic.kr/p/2rMp3pr)

https://live.staticflickr.com/65535/54992492139_cc3961e332_z.jpg (https://flic.kr/p/2rMuU1c)
Field tests continued throughout the 30s and not just receivers. All aspects from studios, cameras, control booths, transmitters, etc.

Here's a slightly later 1933 model.
https://live.staticflickr.com/65535/54992412403_a7ddc9b434_c.jpg (https://flic.kr/p/2rMuuir)

https://live.staticflickr.com/65535/54991349777_450f7fccbc_c.jpg (https://flic.kr/p/2rMp3qi)

A few other experimental models were made over the next few years but none are known to exist.

Which gets us to 1936 when they used all they had learned and started making the model RR-359A using a 9" green phosphor CRT with 343 scan lines for another round of field test.
Come 1937 they upgraded most of the existing "A"s to "B's which included a 12" CRT and 441 lines. Seems they also produced a few more Bs.

Much more info and photos in Television Vol II (https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/RCA-Books/RCA-Television-II.pdf)

https://live.staticflickr.com/65535/54992512493_5be44774d9_c.jpg (https://flic.kr/p/2rMv148)

https://live.staticflickr.com/65535/54992512498_0a0e427761_c.jpg (https://flic.kr/p/2rMv14d)

Perhaps 100 were made in total. It's hard to find exact #s. I'm combining multiple published sources and bits picked up from other collectors. Complicated by RCA send a bunch over to the Soviet union to help get their TV industry going.

What I can tell you for sure is that about 15 are known to exist around the world. Most in museums including two in the Smithsonian, one in Tokyo and several in Canada.

Only 4-5 are in private collectors hands. I am now one of them and will be restoring it to the best of my ability and sharing all the details along the way.
https://live.staticflickr.com/65535/54960118046_5351f293c4_c.jpg (https://flic.kr/p/2rJCYjb)

This is important. Wow.

Has yours been upgraded to a white phosphor CRT? Are there any known working examples?

Yes, mine has a pre-production 12AP4. There are three I know of in private collections that work. There is also one at the Early TV Museum in Ohio that was restored but has not been turned on in years.

I'll be visiting that museum soon to take photos and measurements to aid in my project.

OK, here's the good, the bad and the ugly.
This set is rough to put it mildly. If it wasn't, I would not have been able to afford it.
It's my understanding last two examples on the market sold for $35,000 and $50,000!

Here's a nice example of an "A" revision at the Early TV museum in Hilliard Ohio.
Please click for more info.
I typically visit this museum a couple times a year and will take many reference photos next time I go.
https://www.earlytelevision.org/images/rca_rr359-2.jpg (https://www.earlytelevision.org/rca_rr-359.html)

I purchased this set from another collector and can't take credit for finding it "in the wild".
I was however provided some photos taken back then - around 5-6 years ago I think?
https://live.staticflickr.com/65535/54960120021_bca08561ab_c.jpg (https://flic.kr/p/2rJCYUe)

https://live.staticflickr.com/65535/54960366174_fb0a31dee7_c.jpg (https://flic.kr/p/2rJEf5f)

https://live.staticflickr.com/65535/54960366459_2e10a9a3ca_c.jpg (https://flic.kr/p/2rJEfaa)

My "B" cabinet style is a bit different, but otherwise they are very similar.
Right away we can see the front catalin knobs are missing and the tuner looks odd.
The original tuner is gone! Someone drilled a hole in the cabinet and installed a later tuner which I do not have. It was removed by the previous owner who had intended to have the set restored.
As the years went by, he changed his mind and put it up for sale.

Overall, the cabinet is in poor condition and will require extension repairs and refinishing. Lots of veneer separation and loss. Much of the finish is completely gone.

Maybe a job for Fred Taylor?

The back is also missing which had an AC protection interlock.
I'll either need to bypass it or fabricate a new back.
https://live.staticflickr.com/65535/54994125533_cfde9d118d_c.jpg (https://flic.kr/p/2rMDgya)

https://live.staticflickr.com/65535/54993945036_ab0863a387_c.jpg (https://flic.kr/p/2rMCkU9)

https://live.staticflickr.com/65535/54960121951_4c86238ea1_c.jpg (https://flic.kr/p/2rJCZtv)

The leather surround on the beefy speaker has completely rotted away.
https://live.staticflickr.com/65535/54993056232_8a94759a53_c.jpg (https://flic.kr/p/2rMxMFW)

Now for the good. Both chassis are present and mostly intact. Also, the prototype 12AP4 CRT appears to be good - (have not tested it yet).
The set had already been disassembled when I picked it up with the CRT safely packed away.
https://live.staticflickr.com/65535/54994229260_701955267d_c.jpg (https://flic.kr/p/2rMDNoy)

https://live.staticflickr.com/65535/54994188434_15fa11a010_c.jpg (https://flic.kr/p/2rMDAfE)

https://live.staticflickr.com/65535/54960295498_a0a173c88f_c.jpg (https://flic.kr/p/2rJDT4G)

https://live.staticflickr.com/65535/54960368264_2de5cf8ec6_c.jpg (https://flic.kr/p/2rJEfGh)

https://live.staticflickr.com/65535/54960418445_c04e2e1b52_c.jpg (https://flic.kr/p/2rJEvBt)

This is going to be quite an undertaking!
https://live.staticflickr.com/65535/54960421325_32f07664c8_c.jpg (https://flic.kr/p/2rJEwt8)

https://live.staticflickr.com/65535/54974140213_4d6631164a_c.jpg (https://flic.kr/p/2rKSQBF)

"This is going to be quite an undertaking!" You have doggie there to help!

Thanks for the info. I have a wealth of info about the original tuner will get back to it in a bit. It's similar to what you describe but continuous tuning.

Next, let's take a look at the massive power supply. Easily 100 pounds.
This is a sign of the times. Electrolytic caps were still a fairly new thing. Only four in the whole set and three are in parallel!
Most of the filtering is done by massive filter chokes - even the high voltage.
https://live.staticflickr.com/65535/54995941108_c11aa4f5b7_c.jpg (https://flic.kr/p/2rMNzgb)

This chassis is mostly original. Just one major repair.
The original HV transformer has been replaced with one from a later TRK-12 model.
Not exactly a perfect fit. They added a support bracket on one side. The other side is held down by some twisted wire.
The original was held down by metal tabs fitted through slots in the chassis and bent over as was RCAs construction technique at that time.
The original also had all the wires coming out the bottom while the HV leads comes out the side of this one.
A bit ugly for sure, but I'm unlikely to find anything better anytime soon.
https://live.staticflickr.com/65535/54996018794_96daf52d8f_c.jpg (https://flic.kr/p/2rMNYmA)

This also led to another issue. This set uses two HV rectifiers. One for focus and one for the main HV supply. That means we need two independent, insulated 2.5 VAC secondaries. The TRK-12 only uses one and a voltage divider for the focus voltage.
Well, that means they had to add a dedicated filament transformer.
That's the open frame transformer we see here surrounded by capacitors.
https://live.staticflickr.com/65535/54996018799_3f6d8bef6e_c.jpg (https://flic.kr/p/2rMNYmF)

Speaking of caps. These are the four electrolytics I mentioned. Three 18uF connected in parallel for the main B+ filter and a 10uF for the push-pull 2A3s plate supply.
The two at the top are originals while the others are replacements. It would be nice someday to replace them with period correct caps so they all match.

The gnawed box to the left also contains caps. Two 10uF and a 50uF but they are not electrolytics.
They are foil, paper and wax encased in tar. The are a couple more blocks like this on the upper chassis.
That's good for me as they are easy to restuff.
I will be using high quality polypropylene film caps to replace them all.
https://live.staticflickr.com/65535/54996058444_71ecc0741f_c.jpg (https://flic.kr/p/2rMPb9d)

The HV supplies are brute force half-wave rectifiers on the 60Hz transformer secondaries.
That's why they needed so much filtering. PI filters - two caps with a choke between them.
I've been told the HV caps are oil filled and likely fine so I'll leave them alone for now.
It uses and 878 and 879 rectifier tubes.
https://live.staticflickr.com/65535/54995941113_358d77feee_c.jpg (https://flic.kr/p/2rMNzgg)

Not many parts down below. Mostly some bleeder resistors in the HV supply.
Six 1M resistors in series right across the 6kV supply.
1kV on each is pushing them hard as 2W resistors are typically spec'd at 750v.
I'll upgrade them when I build replica replacement dogbones.
The phenolic board is warped and cracked. I may attempt to repair or replacement might be a better option.
https://live.staticflickr.com/65535/54996047394_3a89e9f2bb_c.jpg (https://flic.kr/p/2rMP7RG)

Some rewiring will also be required.
This set uses a mix of brittle failing rubber wire and cloth covered.
I'll try to match them as best I can with new wire.
https://live.staticflickr.com/65535/54996018814_784a8b818b_c.jpg (https://flic.kr/p/2rMNYmW)

Here's the PSU wiring diagram and chassis photos.
This and really all the incredible service info and photos I have are courtesy of Darryl Hock.
I think it's fair to say without his fabulous cache of info and vast knowledge of these sets this project would be nearly impossible.
There were never intended to be sold to the public and there's no Riders or Sams Photofact.
https://live.staticflickr.com/65535/54996703863_5602f447ee_c.jpg (https://flic.kr/p/2rMSu18)

https://live.staticflickr.com/65535/54995645432_212cec1f16_c.jpg (https://flic.kr/p/2rMM4nj)

https://live.staticflickr.com/65535/54996830895_c8aa9e1ab0_c.jpg (https://flic.kr/p/2rMT8Lk)

That information should probably be scanned and uploaded to the ETFs website if it isn't already. Documentation like that should be preserved.

I wonder how similar your TV is to the RCA displayed on FDR's home in Hyde Park, NY? FRD spoke at the 1939 World's Fair in New York City and was given a TV. He gave it to his mother with whom he lived. She had an office in a nook between the main house and the library. He told her to put in the back corner because he didn't think television was going to amount to anything.

It was many years ago when I saw it and the guide said there were no plans to restore it.

If anyone could tackle this it would be you. Off you go!

FDR had a TRK-12. Conceptually similar, but it used newer tube types like the 1852

Sure, it will be like eating an elephant, but what a reward! I have zero doubt that it will work again. You might need to install a hoist to move that power supply chassis.

That CRT alone is a piece of art.

LOL, yes that would be handy. I've already order up a heavy duty lazy Suzan turntable to put it on.

Now let's take a closer look at the upper chassis. Here's where things get really ugly.

Here it sits just after I got it home.
https://live.staticflickr.com/65535/54960123906_5dec63fbd6_c.jpg (https://flic.kr/p/2rJD14d)

As mentioned earlier, the tuner is gone. It was originally a continuous tuner covering around 40-90 MHz.
Some sort of later tuner was hacked in where all we see all those blue labelled wires. Some run down through an empty tube socket. That's the mixer tube which I assume wasn't needed.

Also, notice there is an empty tube socket on the left side. That's for the 1-V damper tube.
https://live.staticflickr.com/65535/54960423110_07549acdf2_c.jpg (https://flic.kr/p/2rJEwZU)

I popped a new one in and didn't think much of it until I noticed a more modern octal tube socket had been added at the bottom of the chassis.
https://live.staticflickr.com/65535/54974216259_5c2e7b59ea_c.jpg (https://flic.kr/p/2rKTedP)

https://live.staticflickr.com/65535/54998530196_1fa51ea52a_c.jpg (https://flic.kr/p/2rN2QUC)
I found a 117Z6 full wave rectifier tube in it with the filament connected directly to the AC line. Sure enough, it was wired to replace the 1-V damper.
https://live.staticflickr.com/65535/54998530191_400cc773cd_c.jpg (https://flic.kr/p/2rN2QUx)

While we're down here. Notice the mess? There are two candohm resistors down there with many taps.
Likely some sections have gone bad and were bypassed with external power resistors.
There wiring is also a mess and some caps have been added. How do I know? More on that in a bit.
https://live.staticflickr.com/65535/54998698248_d82957e7af_c.jpg (https://flic.kr/p/2rN3GS5)

Now, for the last major bit of ugliness.
This was the vertical oscillator consisting of a 6A6 dual triode and blocking oscillator transformer.
Instead, we have this mess. The original subassembly is completely gone and replaced with an 884 thyratron.
More commonly seen as the timebase oscillator in early oscilloscopes.
I suspect the original transformer went open and this substituted for it.
https://live.staticflickr.com/65535/54974260000_dc222b1b7b_c.jpg (https://flic.kr/p/2rKTsdY)

By the way notice the 001073 stamped on the chassis? Remember that.
https://live.staticflickr.com/65535/54960369709_1746217991_c.jpg (https://flic.kr/p/2rJEg8c)

I intend to restore the original circuit.
Nice thing is the horizontal oscillator is nearly identical, and I can use it as a model.
https://live.staticflickr.com/65535/54998844715_b166ab0fe9_c.jpg (https://flic.kr/p/2rN4spn)

The last bit of ugliness (so far) is all the tacked in caps. None of these are original or should be in these locations. Instead, there should be a box containing two this is missing.
The rest should be in a box on the other side. The box is still there but bypassed. I'll be restuff / fabricating as needed and restoring the original wiring configuration.
https://live.staticflickr.com/65535/54974140373_a996116041_c.jpg (https://flic.kr/p/2rKSQEr)

I mentioned the "001073" stamped on my chassis earlier. This is why I pointed it out.
RCA took fantastic, clear, detailed photos of the various parts of this set.
Turns out the photos are of my chassis!
That leaves zero doubt of what it originally looked like before the 12" factory upgrade to a "B".
It's also neat to see the wooden support jig. I'll fabricate something similar for the workbench.
Otherwise once I unmount that CRT funnel the chassis will tip over.
https://live.staticflickr.com/65535/54999839055_e5f756a85c_c.jpg (https://flic.kr/p/2rN9xZa)

So much neater before all the repairs and modifications.
Notice no caps on the left side and how clean it is along the bottom?
This is what I am striving for.
https://live.staticflickr.com/65535/54998646662_9befc5765c_c.jpg (https://flic.kr/p/2rN3rwE)

https://live.staticflickr.com/65535/54974140213_4d6631164a_c.jpg (https://flic.kr/p/2rKSQBF)

This wiring guide will also be a fantastic guide as it not only shows all the wires but also the original colors.
Now some of the changes are factory from the "B" upgrade. They added a 6H6 tube for example.
So, I'll need to be cautious before I start clipping parts out.
https://live.staticflickr.com/65535/54998646667_e600421bb1_c.jpg (https://flic.kr/p/2rN3rwK)

What are the odds that crt is still useable

Pretty good I imagine. These sets tended to be lower hour since they were so quickly obsolete.

I wonder when the red numbers were added? Perhaps during the "B" upgrade? They
do correspond to designators in the service info.
Also, note the "EXTRA" 6H6 just to the left of "5". This was an RCA factory mod that many surviving examples also have.
https://live.staticflickr.com/65535/54998882972_548d37b25e_c.jpg (https://flic.kr/p/2rN4DLY)

All this leads me to wonder who did the later extensive modifications?
Who would have had this set and the extensive knowledge?
It's also a bit sloppy or downright odd in places.
Like the 117Z6 damper tube?
If it was done in the late 40s or after, why not use an actual damper tube like the common 6W4?
Also, why would you when there was a flood of more modern sets on the market.
The bandwidth and resulting image would not be the best.
https://live.staticflickr.com/65535/54999768341_a8312178fb_c.jpg (https://flic.kr/p/2rN9bXX)

Can you sub that crt with a more modern 12Lp4 if Need be

Not easily. Different deflection angle, anode connector and filament voltage. Also, magnetic vs electrostatic focus

Well maybe you should check that tube before getting in to deep unless of course you have a nos tube ��

If it's bad, I'll come up with something. I knew what I was getting into when I got this set.

Well good luck I hope it tests good

Not easily. Different deflection angle, anode connector and filament voltage. Also, magnetic vs electrostatic focus

You said a 12AP4. And the literature clearly says magnetic deflection even
for the 9 inch CRT. A 12LP4 will work.

I said electrostatic focus - not deflection.

Sure, you can use a 12LP4 if you:

* Modify the filament voltage from 2.5 to 6.3
* Swap out the HV connector
* Hack up the metal funnel to handle the shorter CRT
* Possibly swap out the yoke because of the steeper deflection angle
* Somehow add magnetic focus and disable the high voltage focus supply

That's really cool that it's the same chassis as RCSs period documentation pictured!

It's possible if that set was being used during WWII (maybe with development of bomber cameras or as a monitor at an NBC TV station, or in a military hospital in the US) and the 117Z6 was a wartime tube shortage workaround to the correct tube being unavailable. IIRC the 117Z6 was available prewar and used for the AC supply in Battery/AC portable radios...I have to wonder if it needed it's own isolation transformer to avoid heater-cathode shorts.

RCA was factory updating their 39-40 models as late as 48 and probably supporting them longer...They kept prewar sets around for that and may have kept this around for some purpose that required it to work.

The 12AP4 can be tested on a modern tube tester. I checked mine (after dealing with bad soldering on the heater pins) on my B&K 466 using 10BP4 settings for everything but the heater and was able to get a decent idea of emissions.

They ran the 117Z6 filament directly to an AC plug. This tube is dated 1949 but the type appears to have been introduced in 1940.

So, it's entirely possible the modification was made during the war and I have a later replacement tube installed.

What's also odd in the set is the wiring used for some of the mods. Some is solid 14 gauge house wiring, some stranded. Sometimes several lengths of different types spliced together. That leads me to believe someone was using whatever they had lying around.

If it was an RCA employee, I would think they'd have access to better quality parts.

OK, how about that tuner?
As mentioned earlier, the mixer is on the mains chassis. There is also no active RF front end.
The only active device on the tuner is a type 76 tube used as the local oscillator.
It is continuous with three ganged capacitors. Tuned antenna, mixer and Hartley VFO for the LO.
Those coils are wound next to each other on a common form for coupling.
Dead simple and badly radiates the LO back through the antenna!

Darryl to the rescue once again :D
https://live.staticflickr.com/65535/55001867351_4075f0293e_c.jpg (https://flic.kr/p/2rNjWVM)

Here's the schematic from the original "A" version.
Note the use of an experimental A-305A tube. Mine is missing, but a 6D6 may work well enough.
https://live.staticflickr.com/65535/55002169355_8b29faa8da_c.jpg (https://flic.kr/p/2rNmuGK)

Later revisions used a rotary switch 6J5 and 1852.
Big thaks to Dave AKA "streetmechanic14" for this photo
https://live.staticflickr.com/65535/55002177845_6e586a491b_c.jpg (https://flic.kr/p/2rNmxe8)

Very similar to the Meissner design.
https://live.staticflickr.com/65535/55002130004_daf838c8c8_o.png (https://flic.kr/p/2rNmi1h)

I'm going to experiment with a ganged cap salvaged from a Hallicrafters shortwave radio with similar range to the original.
Not necessarily going to be the final tuner I use in the set, but I figure it will be fun to try and get something going.
https://live.staticflickr.com/65535/55002144579_070c2426cf_c.jpg (https://flic.kr/p/2rNmnkz)

Darryl also kindly identified the parts in the photo using designators from the schematic. This will be a big aid.
L1/2/3, L45 and L4 are the coupled coils wound on a phenolic form.
I'll also examine one in person at the Early TV museum soon.
https://live.staticflickr.com/65535/55002188385_b0c4efb03b_c.jpg (https://flic.kr/p/2rNmAmR)

Best of luck with the project Bob. Just getting the TV to be an accurate reproduction of the original components and condition will be intense.

What are you going to use as a signal source to try this TV out when you complete the restoration?

It should work fine with a modern 525 signal source. Otherwise, there are standards converter kits for 441 line.

I was more concerned about the modulation schemes (Video: vestigial AM and Sound: FM). I guess they had that ironed out before 1936.

I believe the 441 line upgrade did realign the IF for 4.5MHz audio carrier spacing and VSB. The sound detector is AM but will handle FM to some extent. Quality and volume won't be great but we should hear something,

With sets selling as fast as the plants could crank them out in '49, if this one was available for free to someone, I could see someone dumping a bunch of time into it...with hopes of having television for "nothing". It's hard to imagine it impressed anyone with those hacks but, heck, people were buying 3" Pilots. I could see guys like us giving it a try if we were around back then.

Making it look right will prove, I feel, quite a bit more of a challenge than making it work. But 100%, it will happen.

From July 1936, the RCA television field trial was tested on the FCC authorized experimental frequency band: 44 to 50MHz. In 1938, the FCC authorized the band 39MHz to 44MHz for Armstrongs FM experiments.

From July 1936, RCA television utilized on the 44 to 50 MHz band a video carrier frequency of 46.5 MHz and an aural (sound) carrier frequency of 49.75 MHz. This meant the video audio carrier spacing was 3.25 MHz and the video bandwidth for 343 line interlaced at 60 fields per second was 2.5MHz.

Video Modulation: Amplitude Modulation (AM), double sideband.
Audio Modulation: Amplitude Modulation (AM), double sideband.

343 line television used thru 1936-1937 was pre Kell Factor. The introduction of the Kell Factor in late 1937 early 1938 allowed for the increase of lines to 441. Video transmission was still AM double sideband with the same 3.25MHz video-aural carrier spacing.

In April 1939, about a couple of weeks prior to the the television demonstration, RCA switched to VSB with the video- aural sound spacing I believe at 4.5MHz at that point. There must have been a jump in horizontal resolution which was maintained until 1941 with the NTSC adoption of 525 line and reduced relative horizontal resolution with the 0.6 Kell Factor.

Note that the UK 1934 BBC 405 line standard was designed with pre Kell Factor of unity. I recall reading of CBS engineers visiting the UK in the 1950s viewing BBC 405 pictures and remarking how sharp the images were. (Although that may have been mostly due to the 4.5" image orthicon tubes the British were using at the time).

So the move to VSB was not until April 1939 which means the 1937 set most certainly would have had a 3.25MHz sound spacing and only a 2.5 MHz video bandwidth. If a 525 video was to be applied, the pictures will be quite soft unless the amplifier design is modified. Also because the IF band in this set was from around 8 to 14 MHz, altering the response to achieve a good vestigial sideband response with accurately place Nyquist slope could be a bit of a challenge.

Lastly the horizontal sweep frequency of 343line was 10,290Hz. (Not far from the 405line horizontal sweep rate of 10,125Hz). Moving it to 15,750Hz and ensuring efficiency and linearity may be (or once was) a challenge. My guess is some of the changes were done likely professionally initially by the factory and later hacked for NTSC 525 and FM sound with the hacked new tuner.

I expect you will discover interesting attempts to more or less enable the set to cope with the later NTSC signal. But it would be interesting to see it perform as originally intended on 343 or 441 lines.

The information on the 1930s RCA television development is well preserved in the RCA publication of Television in five volumes. I have attached a link to Volume 1 covering 1933-1936.

https://archive.org/details/televisionvoli1901unse

A few corrections:

Their 343 line standard was 2.25MHz. From the "TEST INSTRUCTIONS FOR THE R.F. ALIGNMENT OF THE RC-199 TELEVISION RECEIVER" document attached.

The resolution was 1.5MHz not 2.5MHz as listed and graphed in the "HIGH DEFINITION TELEVISION RECEIVER NINE INCH MIRROR LID CONSOLE TYPE RR-359" manual. A copy of my manual can be found here: https://www.earlytelevision.org/pdf/rca_rr359_manual.pdf

Dr Kell devised the "Kell Factor" in 1934 well before the design of these sets so it was in use when these sets were designed. The RR-359A's have a Kell Factor of about 0.6.

The vid/aud spacing was changed to 4.5MHz in 1937 when the sets were upgraded to the 12" RR-359B's. All the video IF's and mixer were swapped out for the "B" upgrade per the "CHANGE FOR CONVERTING RC-199 TO RC-199B" engineering document. This doc also outlines various component value changes throughout the chassis.

No changes to the horizontal sweep needed to be made. They run efficiently from 240 to 625 lines with full width and good linearity.

All pre-war television run fairly well on FM audio using slope detection. RCA put out a letter to all registered owners after the change in 1941 that they would align their sets for slope detection at no cost.

2.25 MHz sound spacing was used in 1933-34 not for the 1936 343 line and 441 line broadcast tests from July 1936. It is described in the volume 1
Television.

Do not confuse this with the earlier 240 tests described.

Goldsmith described that RCA engineers arrived at a 6MHz channel without the details of the video-aural carrier frequency spacing. You have to dig a bit to find the information.

But think logically about this: they identify the carrier frequencies which would fit nicely in the 44MHz to 50MHz channel. The RCA Volume 1 Television explicitly lists the sound carrier as 49.75MHz and the video carrier at 46.5MHz. The difference.is 3.25MHz.

The video aural carrier spacing could not be moved to 4.5MHz until after the modification from double sideband to vestigial sideband which RCA made immediately before the 1939 World's Fair. Your documentation identifying the change must be from 1939 not 1937..
I know this is correct. I encourage you to look for it. If you require further evidence I will dig it out for you.

Find attached pg 17 from volume 2 of Television, "Recent Developments in Television". Note how the 343line 3.25MHz video aural carrier spacing was also used for 441 lines.

Next I will look for evidence of the 4.5MHz video aural carrier spacing switch. 4.5MHz spacing could not be used for the AM double sideband transmissions prior to April 1939.

What I've stated was not guesses or extrapolations. I am very familiar with all of RCA's television development from 1928 thru the TRK sets as I have most of the original manuals, engineer notebooks, schematics, photographs, etc., part of which I have shared with Bob. I have quoted from my original RR-359 service manual and RF alignment engineering supplement and the RR-359B engineering change log. I have provided Bob with the schematics and photographs of his set. All these documents came from the original RCA engineers, DeHaven, Holmes, Carlson, etc.

I am familiar with the specifications, performance and operation of my own RR-359A1 and RR-359B and other prototype sets. I enjoy looking through the Television series books, but there are many deliberate misdirections, like the LO being coupled through the tuning capacitor shaft on the continuous 359 tuner. I'll stick with the original engineering documents and the actual sets :)

Darryl

I found the transition to 4.5MHz spacing was done in March 1939, a month ahead of the 1939 New York World's Fair. It was published in Television volume 3 (1938 to 1941) in the paper " A Vestigial Side-Band Filter for use with a Television Transmitter", pages 251-2. Page 253 Fig. 1 depicts the interim 1939 VSB channel with 3.25MHz Video-Aural spacing and the 1939 to 2009 VSB channel with 4.5MHz Video-Aural spacing.

The added video channel bandwidth allowed by the increase in the video-aural carrier spacing from 3.25MHz to 4.5MHz certainly would have improved the horizontal resolution. It was in the spring of 1941 that the horizontal resolution would be somewhat sacrificed to facilitate the 525 line NTSC standard.

If only Holmes and Lev had read the Television books before writing the RF Alignment engineering note for the RC-199 (RR-359A main chassis) dated June 22, 1936 ;)

The RC-199 (RR-359A) was 2.25Mhz spacing, the initial change to RC-199B (RR-359B) was 3.25MHz, the final modifications to RC-199B was 4.5MHz.

The notes if dated June 22, 1936 is curious. Clearly the 240 line system had a narrower channel. The frequency response depicted in the second attachment does not relate to the July 1936 test and mail perhaps be a 240 line channel video aural carrier spacing which was approximately 1.5MHz. the 2.25MHz appears perhaps simply to define a reference between the sound carrier position and edge of the video response not the carrier position. Remember this is pre VSB transmission.

It appears development was moving rapidly and the decision to raise the resolution with number of lines which required wider bandwidth may have occurred rapidly. This can be gathered from the volume 1 Television.

The discussion of the 1930's American transmission channel has raised a few questions in my mind pertaining to television receiver design. It may be interesting to compare RCA's development with it's sister Marconi/EMI partner.

The development of the 405 line standard is interesting. It was early and a somewhat premature standard which persisted for nearly five decades. Positive modulation, no equalizing pulses and video delivered AM full double sideband on the original Alexandra Palace transmission channel 1 until 1956. Subequent VHF channels added with the post WWII UK expansion on channel 2 upwards was vestigial sideband. I restored a Baird T5 (1936), an HMV 900 (1937) and a Baird T-18 (1938) and each did not have a tuner. I recall the T5 and 900 used superheterodyne frequency conversion in the video channel. Th Baird T-18 was a straight TRF video receiver with the video rf amplifier tuned to channel 1. (UK prewar receivers were later provided with heterodyne converter adaptors so the prewar sets could receiver other than channel 1.

I also previously restored post war HMV, Bush and Pye receivers. These video receivers were designed for vestigial sideband reception of all the postwar channels. It is important to note that a vestigial sideband designed receiver can properly demodulate double sideband signals without distortion but the opposite is not true. So prewar receivers had to have the video IF response modified to provide a nyquist slope for proper demodulation.

This leads me to the American development of receivers in the late 30's. It must have been noticed early on when designing sets in the effort to reduce the tube count and save money by narrowing the receiver amplifier bandwidth that when tuned to one side with the video carrier on the response sliope that the video baseband response would be extended. In other words the benefits of receiver design cost savings came first even before the consideration of RF spectrum savings.

This leads me to wonder if the frequecy response depicted in figure 2 was an attempt of the earliest implementation of the nyquist slope detection prior to VSB transmission?

The Television series of books can be a decent reference but the articles are taken mostly from RCA Review and are usually "after the fact" of the event as RCA was not one to publish current work in progress.

The RR-359A at the ETF hds been extensively modified after if left RCA and can't be used as a reference for the initial state of these sets. My RR-359A1 and the other RR-359A in a private collection are both 2.25MHz carrier spacing. Television II does mention this.

These sets went through a whirlwind of changes and while I have much of the documentation, there are many things unknown as to when the change actually occurred. For examples: The sets all original had continuous tuners, 7 controls under the lid and a metal crt shield. The 359B's are mixture of continuous/detent tuners, 7 vs 3 controls (the other 4 were rotated down under the deck board), and metal vs the cardboard sleeve later used on the TRK12 which also required a change to the deck board. While all these changes were made to the later B's, I have found no documentation as to when the change over for each occurred.

One RR-359B was modified to be used as the Master Receiver at the 1939 Worlds Fair. Since the LO leakage was terrible from pre-war sets, they could not operate the rows of TRK-12's and RR359B's in the pavilion using RF. This RR-359B was modified with line outputs (a cathode follower for video and an extra audio amplifier) which then fed the display TRK-12's and RR-359B's modified with line input amplifiers. This set has the "regular" RR-359B IF's and the original schematic, while showing the line output modifications, does not show any IF changes. This set works properly on a VSB signal.

(for some reason I can't upload files today, the above reference is in Television II page 35)

The channel spacing is not 2.25MHz. In 1936, the channels were 6MHz spaced.
The 3.25MHz carrier spacing was used from June 1936 thru 1939 when 4.5MHz carrier spacing was adopted.

The figure 2 drawing you depicted is dubious and the information you provided was correct and misinterpreted because the 2.25MHz is referring to the video response not the carrier spacing. It is clear and documented.

And from a purely engineering perspective ithe 3.25 MHz makes sense as it allows the double sideband video and sound carriers to fit into the 6 MHz channel with an appropriate guard band between audio and video.

This is purely academic because as you said the sets have been extensively modified to work on the later standard.

He meant carrier spacing - not channel spacing.
The 343 line standard used in the "A" versions used 2.25MHz carrier spacing.

https://live.staticflickr.com/65535/55007142073_34ef8ba0eb_o.png (https://flic.kr/p/2rNMYVg)

https://live.staticflickr.com/65535/55007234549_42dbf26bb4_o.png (https://flic.kr/p/2rNNspF)

Thanks Bob, that was the page I was trying to post this morning, not that it should be required after posting actual engineering documents. I think I'm done with this thread at this point as it's just going in circles. I have posted pieces of three separate original, dated engineering documents stating the CARRIER spacing to no avail. (I did accidentally interchange channel for carrier and have fixed that)

I guess I'm going to dump all the boxes and binders of dubious RCA engineer's original documents since apparently they did not know what they were doing at the time and junk the sets since we're now informed they can't possible work the way they do :rolleyes:

Sorry for hijacking your thread, hopefully it can get back on track.

Thanks Bob. That appears to be the missing link.

So the transition includes from 1934 thru early 1936 343 lines with a 4 MHz channel and 2.25MHz carrier spacing. For the July 1936 343 line first public demonstration, RCA engineers moved to the 6 MHz channel where it was first used with double sideband video and a 3.25MHz carrier spacing.

The question remains when the 4.5MHz carrier spacings were adopted. The RCA paper said the first time it was applied to the transmitter was March 1939 which agrees with another paper I read indicating VSB was first implemented just prior to the NY World's Fair in April 1939.

Logically VSB was probably first tested on a 3.25MHz carrier spacing channel for direct comparison with 3.25MHz carrier spacing full double sideband. VSB 3.25MHz spacing would not entirely fill the 6MHz channel and so this would suggest by March 1939 4.5MHz carrier spacing was introduced.

So the transition includes from 1934 thru early 1936 343 lines with a 4 MHz channel and 2.25MHz carrier spacing. For the July 1936 343 line first public demonstration, RCA engineers moved to the 6 MHz channel where it was first used with double sideband video and a 3.25MHz carrier spacing.
Last time in the hopes that anyone reading this in the future will not have bad information. The pages from Television II clearly show the 343 was 2.25MHz spacing and the 441 was 3.25MHz spacing.

NO, as all the actual dated original documents that have been presented here have shown, the 343 line field test was NEVER at 3.25MHz carrier spacing. The RF Alignment manual I copied showed they were aligning the 343 line RR-359 sets to 2.25MHz in November of 1936. I fail to understand your instance to the contrary without ever providing a single piece of original documentation of support.

Last time in the hopes that anyone reading this in the future will not have bad information. The pages from Television II clearly show the 343 was 2.25MHz spacing and the 441 was 3.25MHz spacing.

NO, as all the actual dated original documents that have been presented here have shown, the 343 line field test was NEVER at 3.25MHz carrier spacing. The RF Alignment manual I copied showed they were aligning the 343 line RR-359 sets to 2.25MHz in November of 1936. I fail to understand your instance to the contrary without ever providing a single piece of original documentation of support.

I went back to read the Joffieffe presentation to the FCC on June 15, 1936. In it Jollieffe asserts a resolution around 440 lines and the need for a 6 MHz channel. However he explains that the construction of the transmitter for the July 1936 first television demonstration was 343 line and a 2.25MHz carrier spacing.

So the impeding move to 441 line was pending, I have not found a date for it's first public demonstration but i suspect it must have been late 1936 or early 1937.

So for the record, I fully agree with your statement and appreciate your dilligent clarification.

If only Holmes and Lev had read the Television books before writing the RF Alignment engineering note for the RC-199 (RR-359A main chassis) dated June 22, 1936 ;)

The RC-199 (RR-359A) was 2.25Mhz spacing, the initial change to RC-199B (RR-359B) was 3.25MHz, the final modifications to RC-199B was 4.5MHz.

What is interesting is the figure 2 attachment showed the video carrier on the trailing slope of the response curve. That means the RCA engineers realized by June 1936 that economy on TV receiver design could be accomplished with less tubes by using a single sideband. Jollieffe alluded to this on his presentation the the FCC on June 15, 1936 when he suggested if a single sideband could be employed in a 6MHz channel video transmission, greater detail with less bandwidth could be employed. This suggests the RCA engineers by June 1936 knew of the possibility of single sideband delivery but had not yet figured out vestigial sideband operation. That would take another couple of years until 1939!

I'm surprised they didn't use RCA acorn tubes/valves in the
tuner,these were developed by RCA and available by the mid
1930's.Performance would have been way better.954 955 956
series
https://en.wikipedia.org/wiki/955_acorn_triode

I'm surprised they didn't use RCA acorn tubes/valves in the
tuner,these were developed by RCA and available by the mid
1930's.Performance would have been way better.954 955 956
series
https://en.wikipedia.org/wiki/955_acorn_triode

I agree. I have an RCA frequency calibrator from 1935 which used the acorn triode 955. And a 1939 Hallicrafters S27 UHF radio which uses the pentodes. Maybe 1935/36 was a bit too early?

I decided to partially reassemble the set while I focus on the power unit chassis down in the workshop.
https://live.staticflickr.com/65535/55012224172_9d30d1cc07_c.jpg (https://flic.kr/p/2rPf2DE)

https://live.staticflickr.com/65535/55013365609_dd28709010_c.jpg (https://flic.kr/p/2rPkSXB)

I need to remove a bunch of screws and rotate that screen mask 90 degress.
https://live.staticflickr.com/65535/55013282978_ab0531857d_c.jpg (https://flic.kr/p/2rPksoW)

https://live.staticflickr.com/65535/55013420105_64eb87e189_c.jpg (https://flic.kr/p/2rPmaac)

Also picked up an RCA highball glass from the 1939 New York world's fair to celebrate when I get it working.
https://live.staticflickr.com/65535/55013420100_1f83f2f6c6_c.jpg (https://flic.kr/p/2rPmaa7)

A heavy duty turntable makes it much easier to manipulate the very heavy PUI chassis on the workbench.
https://live.staticflickr.com/65535/55013420160_b2a0051874_c.jpg (https://flic.kr/p/2rPmab9)

https://live.staticflickr.com/65535/55012232252_023d832d03_c.jpg (https://flic.kr/p/2rPf53Y)

A real eye towards serviceability the way that chassis is mounted. Now, remember, you're only allowed to use your RCA equipment when testing this. Have to keep it real.

That's a great decal. I wonder if anybody has fashioned a reproduction yet?

I have water slides of the "RCA Television" decals I made on my Alps printer using gold foil. I'll send Bob some.

(artifacts are not in original)

Thank you. I do plan on having the cabinet repaired and refinished.

I started on the PU by checking the resistance of all the transformers and filter chokes.
All appear to be OK, except for the replacement HV transformer. The HV secondary is open.

Out it goes. I wasn't happy with the way it was crammed in there anyway.
https://live.staticflickr.com/65535/55013282983_a80e74db56_c.jpg (https://flic.kr/p/2rPksp2)

I also removed the added 2.5 volt filament transformer.
https://live.staticflickr.com/65535/55013365619_e97a2a93a1_c.jpg (https://flic.kr/p/2rPkSXM)

You can see the scars where openings were enlarged for the TRK transformer.
https://live.staticflickr.com/65535/55013365614_4345df03ed_c.jpg (https://flic.kr/p/2rPkSXG)

I'll be replacing them with two Triad filament and a neon sign transformer.
https://live.staticflickr.com/65535/55014164949_72a5734337_c.jpg (https://flic.kr/p/2rPpYzk)

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I'd been tipped off that an RCA radio from the 30s might have a suitable shell.
That trigger a memory that I had parted out a rough 1930 Radiola 80 years ago.
I went hunting in the garage and sure enough I still had the power chassis.
Bingo! The largest box is exactly the right size!
The three new transformers should fit nicely inside and I can restore the wiring to the original configuration.
It will also hide the cuts made in the chassis.
https://live.staticflickr.com/65535/55013365684_82f23104d3_c.jpg (https://flic.kr/p/2rPkSYU)

I need to bake out the contents and strip the brown paint.
A few taps and it will drop into place.
https://live.staticflickr.com/65535/55013365694_8df41fc115_c.jpg (https://flic.kr/p/2rPkSZ5)

While I wait for new transformers to arrive, I can start on restuffing this box capacitor.
https://live.staticflickr.com/65535/55013420120_44d2d46279_c.jpg (https://flic.kr/p/2rPmaas)

Mouse chews there? Damn rodents!

Looks like it. That's about as far as they got though thank goodness. No rodent urine corrosion to deal with.

Moving on to the bleeder resistor board. It's warper and cracked. Seems they added a ceramic standoff during the "B" upgrade which put stress on the board.
You can see the two holes where it used to have a metal support like on the other side
I'll fabricate replica dogbones using this technique (https://youtu.be/0ddMuSt_aR4?si=1rLXDGvrRtlyLhqu) and repair/replace the phenolic board


https://live.staticflickr.com/65535/55013365654_6963da60ec_c.jpg (https://flic.kr/p/2rPkSYo)

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https://live.staticflickr.com/65535/55013111801_a489bcd886_c.jpg (https://flic.kr/p/2rPjzvB)

I guess you want to be as authentic as possible, but I wonder if, since you're going to use modern resistors in handmade dogbone shells anyway, why not keep the original resistors in place on the phenolic board but take them out of circuit while mounting the new resistors in circuit hidden on the back of the board? The original resistors could be kept for display on the front while modern resistors do the actual work on the back. Would save the time and effort of making new/old looking resistors and you'd keep the originals.

Some transformers have arrived.
Both are well made and should fit inside the salvaged transformer box.
Not sure if I can fit another Triad filament transformer in there though. If not, I'll hunt around for a smaller one. Don't need 10A for the 2X2 filament.
https://live.staticflickr.com/65535/55019885476_92bb4381dc_c.jpg (https://flic.kr/p/2rPVi67)

Bob, the story about the “001073” stamped on the chassis is one of those absolutely charming coincidences that always make me smile.

And Daryl, I could be wrong but although Ray Kell was surely often the smartest guy in the room, I don’t believe he was a PhD.

Bob, the story about the “001073” stamped on the chassis is one of those absolutely charming coincidences that always make me smile.

And Daryl, I could be wrong but although Ray Kell was surely often the smartest guy in the room, I don’t believe he was a PhD.
Hi Dave
I think you're right. I remember reading an article that called him Dr. but I don't know that as fact. Doing a quick search turns up nothing on him having a PhD.
Darryl

I placed a WTB in the classifieds for two matching RCA caps to make a matched set. Another collector came through with some and we made a deal.
I'd all but given up on these ever arriving after being endlessly delay by UPS, but here they are.
https://live.staticflickr.com/65535/55061880807_7d70eb966e_c.jpg (https://flic.kr/p/2rTCwQx)

I also cleaned out the donor HV transformer box. First, heat to get the old transformer out. Then, cold to make the tar brittle and easy to chip out. Finally, lacquer thinner to remove the residue. It looks reddish due to some rust on top and stubborn paint.

Once a few more supplies arrive in about a week, I'll start restuffing and fabricating.
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Did some experimenting today. 8 turns of wire around the primary will get me 1.5 VAC into a 1.5 ohm load. 4-5 more should get me 2.5 VAC to power the 2X2 rectifier filament. The challenge now is to find wire that can handle 2A or more, 2kV or more and fit around the primary. This experiment is using 600 volt wire and there's no more room.

I suppose I can use enameled wire and some Kapton tape. I believe it is rated for 7,000 volts/mil. After all I'm not concerned about the windings shorting to each other. It's the primary and core I need to worry about.

https://live.staticflickr.com/65535/55082266897_4e860a6cd8_c.jpg (https://flic.kr/p/2rVr1UR)

While waiting for another parts order to arrive, I moved on to restuffing the can capacitors.
Very easy to cut them open by rocking a fresh box cutter blade over the aluminum right below the cap lip.
Here's what I found inside.
https://live.staticflickr.com/65535/55087726417_17a463c2d0_c.jpg (https://flic.kr/p/2rVUZQv)


There appears to be a pressure release value under the cap which should make it trivial to reattach.
I'll try using some big o-rings.
https://live.staticflickr.com/65535/55087726407_641a02bcaa_c.jpg (https://flic.kr/p/2rVUZQk)

The new caps fit easily inside the empty can.
I'll transfer the original terminal lug to some new tinned brass rod and thread it through the base for the positive.

Which leaves the negative. I might try some aluminum compatible solder or sneak a ground lead out through the base.
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https://live.staticflickr.com/65535/55087726412_09c3af1e4b_c.jpg (https://flic.kr/p/2rVUZQq)

It took about 14 turns of enameled wire to power the 879/2X2 tube filament at 2.5 vac. Barely any effect on the HV output of the neon sign transformer.
https://live.staticflickr.com/65535/55095531006_cd5cd1876c_c.jpg (https://flic.kr/p/2rWAZSo)

With a 1mA load, I'm getting 4.6kVAC out. At 1.5mA, it barely drops to 4.5kVAC. So, it seems no need to be concerned about the current limiting core design of the NST in this circuit.

Next, I powered up the 8013 HV rectifier this set came with and it lit up nicely. I then switched to the original 878 type. Holy cow is that thoriated filament bright!
https://live.staticflickr.com/65535/55095531011_11acf5034f_c.jpg (https://flic.kr/p/2rWAZSt)

https://live.staticflickr.com/65535/55095742523_e2c9f58d8f_c.jpg (https://flic.kr/p/2rWC5Ke)

Next up, I'm going to secure the added filament windings, insulated the leads and breadboard both rectifiers with filter circuits and simulated loads for further testing.
https://live.staticflickr.com/65535/55095808284_df1e8bb8c3_c.jpg (https://flic.kr/p/2rWCqi3)

Work continues on the power supply chassis. The second anode and focus filter caps have been removed.
https://live.staticflickr.com/65535/55115483107_56065a2944_c.jpg (https://flic.kr/p/2rYnfW8)

That gunk appears to be wax.
https://live.staticflickr.com/65535/55116355721_82ec67e031_c.jpg (https://flic.kr/p/2rYrJkc)

Now I can down into this area and really clean it out. Lots of residue I presume from when the original HV transformer died.
https://live.staticflickr.com/65535/55117967519_44e3c5a45c_c.jpg (https://flic.kr/p/2rYzZsP)

Here they are after some rust removal and cleaning. They are oiled filled and likely still good. Made from a steel box soldered closed with ceramic insulated lugs.

I'll test them and try using in my test setup before reinstalling them. If either is bad, I'll try to open up and hide new caps inside. Yes, I know they might contain PCBs.

Each contains two caps with a common lead in them. Used in a PI filter configuration with a filter choke between them.

I don't suppose anyone have a clear photo of the original labels? Mine were already gone when I got the set.
https://live.staticflickr.com/65535/55117955304_7348977573_b.jpg (https://flic.kr/p/2rYzVQd)

I've also been experimenting with replacing the rectifier tube sockets.
https://live.staticflickr.com/65535/55116750185_f7e6a59086_c.jpg (https://flic.kr/p/2rYtKAi)

The chassis hole is a bit too small for these more modern plastic and phenolic sockets. Rather than enlarge the hole, I slightly filed down one of the sockets just enough to fit.
https://live.staticflickr.com/65535/55115483162_a2d64d7354_c.jpg (https://flic.kr/p/2rYnfX5)

https://live.staticflickr.com/65535/55116558143_3281dfc17c_c.jpg (https://flic.kr/p/2rYsLve)
Unfortunately, the chassis steel is much thicker than usual so I can't use the snap ring.

I'll likely just go with something that is functional and safe for now while I search for a closer match to the original style.
https://live.staticflickr.com/65535/55115483142_f7abfc462b_c.jpg (https://flic.kr/p/2rYnfWJ)

I tested both caps with a modern LCR meter and a vintage bridge.
Both measure good for capacitance, but the smaller cap used in the focus circuit shows some leakage with only few 100 volts on it.
Should be a dual 0.05uF rated for 2kV or better
I'll attempt to open it up and restuff with a couple high quality plastic film types.

I also received a comment on YT that the focus cap failed and took out the focus HV transformer in the RR-359 at the ETF museum!
I'll be at the museum for the convention in a couple months and will thoroughly examine and document their set.

https://live.staticflickr.com/65535/55119430245_1dd78d6fdb_c.jpg (https://flic.kr/p/2rYHuhe)

It was fairly easy to use some desoldering braid and pop the box open. I carefully drained the oil and pulled out the old caps.
https://live.staticflickr.com/65535/55121481168_d78de90934_c.jpg (https://flic.kr/p/2rYTZWY)

Then, I cleaned it out and disassembled.
https://live.staticflickr.com/65535/55121669600_08ddd77fb6_c.jpg (https://flic.kr/p/2rYUXXN)

https://live.staticflickr.com/65535/55121533374_a06f87a1c9_c.jpg (https://flic.kr/p/2rYUgt5)

I just got this cool military grade HV cap from Surplus Sales of Nebraska. It's made from reconstituted mica.
https://live.staticflickr.com/65535/55134710785_d9367e9921_c.jpg (https://flic.kr/p/2s14NDP)

It's also just a tad too big to fit cleanly.
I'll put some of the blame on them. They listed it as 1.75" wide, but it's actually 1.85" wide.
The length is exactly 2.25" as specified.
If I angle it and shave off a bit of the outer coating I think I can cram it in.
More of a concern are the leads.
The common does not connect to the case. It needs to wrap around down to the center lug on the opposite side.
I think I can just manage it.
This project sure is frustrating. So far just about every part has been oh so close, but not quite right.
https://live.staticflickr.com/65535/55133428262_275fa30e72_c.jpg (https://flic.kr/p/2rZXepm)

The power supply in this set is rather creative. Here's a simplified, partial diagram.
My favorite is how they vary the focus voltage by using a big rheostat on the primary on the focus HV transformer.
I suppose they wanted to avoid having to deal with a high voltage on a user accessible potentiometer.

https://live.staticflickr.com/65535/55134556251_3656f9b3ff_c.jpg (https://flic.kr/p/2s141Hr)

While working on the HV supply, I discovered the Mycalex HV deck had some stress cracks. Probably from the tube being insert and removed over the years plus age.
It's an interesting material. Feels like stone or ceramic, but can be drilled and machined if care is taken.

The breaks were very clean and no damage around the tube pins. So, I figured I try to glue it.
First, I pressed the pieces very tightly together and wicked in some super glue from the back side. It flowed and bonded very well.
I then reinforced and filled in void with slow cure, high tempo grey epoxy cement.
Finally, I gave it a good cleaning. I think it will work.
https://live.staticflickr.com/65535/55154891996_ab51e653b1_c.jpg (https://flic.kr/p/2s2RePJ)

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I have returned from the 2026 ETF convention with a wealth of knowledge and experience. Not only was I able to pull the chassis out of the museum's set, we actually got it working!
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It had been restored some 25 years ago, but it had never been properly reassembled or powered up at the museum.
We spent some time pulling and studying the chassis - especially the tuner. Note this set seems to have an FM descriminator circuit added by RCA.
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Here's the main coil with windings for the antenna, LO and mixer.
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We discovered that the 878 tube had been replaced with an 879 and the focus wire cut. Seems someone was a bit lazy when the chassis were pulled to ship the set to the museum and cut it instead of properly disconnecting it from the screw terminal.
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The rest looked OK so we proceeded with a power up in stages.

First, with all the rectifier tubes pulled. All the tube lit up so we proceeded with the HV rectifier tubes then the 5U4s.
Here it is with an 8013A in place of the 878
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All was going fine but no raster on the CRT. Eventually someone noticed there was a splotch as it powered down. The led us to discover a bad contrast control. Further, we needed to bypass a resistor to get the brightness control into the proper bias range for the CRT.

OK, raster but no image. We tried direct video injection in the grid of the video amp but that didn't go well. So back to the tuner. The original A305A mixed tube grid cap had broken loose. We subbed a 6D6 and after some more control manipulation we finally had a stable image!

Note this set has some sort of CV326 or some such British military CRT installed in it hence the odd phosphor color.
The thin rubber CRT mask shifted out of place while we worked on the set.
Next time we visit, we'll repair the A305A grid cap, replace the bad contrast control and reseat the CRT mask.
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Another curious thing is the mirror in the lid.
This set has a polished piece of (stainless steel) metal and a lightweight lid. You can see some corrosion has started on the right side.
Mine and others have a heavy front surface mirror piece of glass in the lid.
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We attracted quite a crowd as we worked on it.
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Neat to see the tuning dial is a loverly backlit green. Not going to be easy to reproduce it.
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Almost forgot we found this very early style 879 (2X2) tube in the set with a neat, rippled fan filament.
I've been told this is what would have been in mine originally.
Now a new quest to find one!
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:banana:

We will be working on the museum set at some point over the summer and I will gather more information.

Meanwhile, perseverance pays off. It took me a few tries to get there but I finally found a 4 pin tube socket that fits in the RR-359! I will need to slightly enlarge the mounting tab holes, but the phenolic body fits perfectly.

It is an Amphenol SK4P from RF Parts. https://www.rfparts.com/sk4p.html
I recommend perusing their offerings if you are not familiar with the site. They lean towards transmitters and have some interesting vintage parts.

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It's in the foreground here. Body and mounting collar are smaller than the industry standard.
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Obviously, it's not the same as the original, but will get the job done.
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https://live.staticflickr.com/65535/55325875489_e8f8bc1032_c.jpg (https://flic.kr/p/2shXzfZ)

Just found a fan filament 879 courtesy of Vacuum, Tubes Inc. Fingers crossed it arrives safely.

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