1936 RCA RR-359B Restoration

[tubesrule]

Originally Posted by Dave S

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

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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.


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.



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.


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.


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!




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.


That gunk appears to be wax.


Now I can down into this area and really clean it out. Lots of residue I presume from when the original HV transformer died.


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.


I've also been experimenting with replacing the rectifier tube sockets.


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.



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.


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.


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.


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.