type 852 triodes - graphite plate version -why the interesting bulb?

[Opcom]

Among the goodies from the VRPS convention, a pair of 852's came home with me. These are not the more common RCA labeled ones, which as shown in TT-3 have a metal anode with fins, but these have what appears to be thick graphite or carbon anodes. (sorry no pics yet)

They are somewhat coarse black anodes perhaps 1/8" thick wall. There is no brand on the tubes and I am curious as to who might have made them. What advantage would the carbon anode have?

These as a very small amount of 'dust particles' from the anode loose in the tube, but it does not seem to be stuck to anything, it lies near the glass slean in the base. I hope it will not cause issues. I wonder how the dust got loose? These are likely 60 years old.

Lastly, note the shape and construction. The full ratings are only 30MHz, but they go to 70MHz at 75% ratings and 120MHz at 50%. The tube by itself is resonant at 210MHz. I wonder why such an unusual design was used for a 30MHz tube, unless they were used and abused in "SHF" sets of the day.

The highest frequency types in TT-3 -type 800 runs 180MHz at 50% and the 834 runs 350MHz at 50%, and both of those are rather 'normal' looking tubes. The anode of the 852 is not very large, I can imagine it glowing dull red although how this would be watched with the blazing filament is anyones guess. The 800 runs no color, the 834, a barely perceptibe red.

The 852 is rated 100W dissipation/3000V
The 800 is rated 35W dissipation/1250V
The 838 is rated 50W dissipation/1250V

The point above is that the frequency range does not seem to be the factor in the bulb shape. If anything, the internal and flying leads seem to be a limitation.

So what is the fuss about the shape? It must have been very costly. Large bulb necessary to survive the dull red heat of a quite small 100W anode? For the voltage? Opinions about why the particularly cool-looking envelope was made for this tube would be interesting.

(Yeah I want to use them. They deserve to be used a bit, for something decent)

[k4kyv]

I think the odd shape is to accommodate the flexible wire leads.  Otherwise, the tube strongly resembles an Eimac 100-TH, if you imagine plate and grid caps instead of the wire leads coming out of the glass. Those tubes first came out in the 30's, and were touted as "high frequency" triodes. Until then, about the best RCA could do was the 204-A, which was rated at 3 mc/s maximum for full power ratings. Heinz-Kaufmann, and later Eimac, were the first to use the tantalum plate.  Maybe yours were manufactured by Taylor.  RCA's 204-A had a metal plate, while Taylor's were graphite.  RCA may have gone to  graphite in later editions.

Is the tube base white ceramic, brown phenolic (like a 1625) or metal?

[W2VW]

Looks like a way to support all the elements without any ceramic material inside the vacuum.

[W3SLK]

What's truly amazing is that tubes like the 100-T(x) were used in early radar systems!

[DMOD]

I think it was an answer to a  thermodynamics problem and a interelectrode capacitance solution.

The leads not only carried some of the thermodynamic load, but also reduced capacitance due to their spacing.

Phil - AC0OB

[Opcom]

Is the tube base white ceramic, brown phenolic (like a 1625) or metal?

It is a plain aluminum-looking base with only "852" stenciled on it in black, in a font reminiscent of rounded military stencils of the time.

[WBear2GCR]

...I use them for the front end of my phono preamp...

[KM1H]

RCA used that odd shape and on several tubes including the 860 and 861 tetrodes of the 20's using metal plates. HF Military QRO equipment only went to 18mc and low power was used above that for short range work.

The 100T was stiill a dream and didnt break any new ground except for repeatability and reliability which was manufacturing driven. Raytheon also built a lot of metal plates.

[Opcom]

...I use them for the front end of my phono preamp...

There is something to be said for higher voltages on the plates of preamps.