1936 RCA RR-359B Restoration

[bandersen]

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.


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.

[timmy]

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

[bandersen]

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

[timmy]

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

[bandersen]

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

[timmy]

Well good luck I hope it tests good

[dtvmcdonald]

Originally Posted by bandersen

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.

[bandersen]

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

[Electronic M]

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.

[bandersen]

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.

[bandersen]

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


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.


Later revisions used a rotary switch 6J5 and 1852.
Big thaks to Dave AKA "streetmechanic14" for this photo


Very similar to the Meissner design.


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.


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.

[Chris K]

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.

[Tom9589]

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

[bandersen]

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

[Tom9589]

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