Posted this on ARF too, where I got the NIB 237s, but thought I might get a different answer here since I referenced the use of the tube in a Philco radio:
The 6 NIB RCA 237s I just bought, and very happy with, from our want ads:
http://www.antiqueradios.com/forums/view...5&t=278649
Well all of the boxes and the very nice included spec sheet say that they need DC on the filaments. I had always thought of a 37 as a 6.3V 27 which is fine on 2.5V of AC. I looked in the early RCA tube manual and sure enough, specs out DC filament. So the use of 5 or 6 Philco labeled "37s" in my 115X are wrong (also globes)? Or did other manufactures build them with different heater/cathode specs? Or did they change the tube OR the spec sometime along the way. OR did Philco just ignore the spec?
The Philco 37 tubes (which were made by Hygrade/Sylvania) operated on 6.3 volts AC in 1932-33 Philco home radios, and on 6 volts DC in Philco Transitone car radios which used the tube.
And in the 1932 Philco home radios, the 37 was used where the 27 had been used in similar 1931 Philco models.
The 37 was also used in the 16, and I believe in the 116 as well.
We would need to see a 1932 Sylvania tube manual to see what their specs were for the 37. I have never heard of 37 tubes specifying DC only on the filaments.
*****
While in the midst of writing this, I did some research online.
There is a Sylvania data sheet (in French) here:
http://tubedata.milbert.com/sheets/121/3/37.pdf
Not speaking French, I can only assume that "CA ou CC" is French for "AC or DC"?
An RCA spec sheet for the 37 is here:
http://tubedata.milbert.com/sheets/021/3/37.pdf
and it states "AC or DC" for the heater.
I also looked at the NJ7P page, and it states that an RCA manual from 1932 specified DC only, while a 1937 manual did not specify DC only.
Hmmm...
I wonder now if Philco just stuck them in their 1932 models and found that they worked on AC? I see both versions had heaters rated at 0.3 amps.
Yes they are ptobablyi 37's yeah, used in auto radios too from one source. Should work in any environment as well.
If all of these tubes have an indirectly heated cathode then they should work on either AC or DC. Why would anyone bother using a an indirectly heated cathode in a DC only tube when they could use a directly heated one which is simpler to construct?
Regards
Arran
Be that as it may I have never had issues with any 37 "globe" tube that I have installed in my AC sets.
Here are data sheets for both the type 27
http://frank.pocnet.net/sheets/021/2/27.pdf and type 37
http://frank.pocnet.net/sheets/021/3/37.pdf tubes. The main differences are that the type 37 uses a 6.3 V filament and the type 27 uses a 2.5 V heater. The type 37 also has higher output than the 27. Both tubes can be used on either AC or DC since they use a separate heater and cathode. On older sets with tubes which used the filament itself for the cathode, often one finds a resistor with a variable center tap, a potentiometer, used across the filament, and the cathode connection made to the center tap, where such a tube was to be powered by AC. The center tap was then adjusted to minimize "hum". Very soon though, when indirectly heated cathodes began to be used, with 5 pin bases, such as the 27 and 37, this was no longer necessary, and by merely changing to a 5 pin base, and appropriate re-wiring, one could convert a battery powered set to use AC for the filament supply, the biggest hog of electrical power, eliminating the need for bulky car batteries and battery chargers.