[Ron Ramirez]

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.