The PHILCO Phorum

1. I wonder why Philco used big pin tubes in this radio (78, 80, 37, 42)? Philco was heavy into loctal in late 1939. Other sets like the 39-770 use octal.

2. Capacitor 88, the volume motor phase shift capacitor, is listed as 30uf 30volt electrolytic. Mine is bad. I subbed a 12.5uf AC motor starting cap and the motor runs. Can this REALLY be electrolytic, or should it be an AC or back to back electrolytics?

3. The RF amp tube has an apparently original 6K7G installed. But the schematic shows a 6J7G, as does the tube placement chart. But the alignment trimmer locations chart shows a 6K7G. This tube has AVC voltage applied, so I would suspect it should be a 6K7G.

4. The detent ball (or whatever) is missing from the bandswitch. In other cases I just installed a ball bearing or stole the ball from another switch. But this one has a tit on the arm above where the ball should be. So it looks like the detent ball has a hole in it. Does anyone know what this part looks like?

I plan on ordering a set of service notes for this radio if available. Maybe that will answer some of the questions.

Thanks for all the time.
Dave

1. It was around this time (June 1940 to be exact) that Philco bought controlling interest in the National Union Radio Corporation, a manufacturer of vacuum tubes. Unconfirmed rumors have persisted for years that with the National Union acquisition came a huge stock of standard-base tubes (41, 42, 80, etc.), so Philco started using the standard base tubes again to use up surplus stock. I cannot confirm or deny these rumors.

2. Use a motor run capacitor, as close to 30 uF as you can get and as close to 30 volts as you can get. I have used a Dayton motor run capacitor, obtained from a motor rewinding shop and about the same physical size as the original, in these sets before with excellent results. 120 volt motor run caps are overkill, not to mention too large physically to fit in the chassis.

3. Go with 6K7G. The set's AVC will function better with it than with a 6J7G.

4. Sorry, can't really help you on this question. It seems that every one of the 1939-42 Philco models with thumbwheel controls have band switches that do not "click"; it is as if all of them have lost their ball bearing or whatever provided the detent action.

Regarding the bandswitch, I took a closer look at the detent plate. There is NO indication of either wear or grease, oil, dirt, etc. It appears that this radio NEVER had a detent ball or whatever (either that or it lost it VERY early in its life).

The big pin tubes in this radio, likely original, were branded 80 and 78 (Sylvania), 42's (RCA), and 37 (Philco) and not National Union, for what that's worth.

I have had no luck finding a low voltage 30uf motor run capacitor. So far, the lowest voltage found (shops as well as manufacturers) was 125 volts. But the good news is that there is plenty of room under the chassis for a 22-30uf 125 VAC motor run cap.

Dave

Hi Dave

I feel you are right about these sets never having had a detent ball, or whatever. I have never found one with thumbwheel controls that "clicked" when changing bands.

About the tubes - the original tubes shipped with the radio would have been Philco brand. A new Philco at that time would definitely NOT have RCA tubes in it! Philco and RCA developed a very adversarial relationship from 1930 on, culminating in a suit and countersuit or two - see my History section:

http://www.philcoradio.com/history/index.htm

I honestly do not remember the voltage of the Dayton motor run cap I bought a long time ago to install in a 39-116 set. If your 22-30 uF cap fits...by all means, go for it!