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.

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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.

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.

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 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.
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I need to remove a bunch of screws and rotate that screen mask 90 degress.
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Also picked up an RCA highball glass from the 1939 New York world's fair to celebrate when I get it working.
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A heavy duty turntable makes it much easier to manipulate the very heavy PUI chassis on the workbench.
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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.
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I also removed the added 2.5 volt filament transformer.
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You can see the scars where openings were enlarged for the TRK transformer.
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I'll be replacing them with two Triad filament and a neon sign transformer.
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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.
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I need to bake out the contents and strip the brown paint.
A few taps and it will drop into place.
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While I wait for new transformers to arrive, I can start on restuffing this box capacitor.
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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 and repair/replace the phenolic board


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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.
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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.
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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.

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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.
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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.
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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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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.
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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!
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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.
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Work continues on the power supply chassis. The second anode and focus filter caps have been removed.
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That gunk appears to be wax.
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Now I can down into this area and really clean it out. Lots of residue I presume from when the original HV transformer died.
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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.
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I've also been experimenting with replacing the rectifier tube sockets.
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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.
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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.
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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.

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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.
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Then, I cleaned it out and disassembled.
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I just got this cool military grade HV cap from Surplus Sales of Nebraska. It's made from reconstituted mica.
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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.
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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.

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

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