11-11-2012, 08:24 AM
Hang on John, help is on the way...
OK. The original Philco 37-89 schematic calls for a 0.25 uF cap in parallel with a 700 ohm resistor from the IF tube cathode to ground.
I checked in the Philco Changes in Models file (available here), and there was a change in Run 5 of the 37-89 where both IF transformers were changed, an extra winding was added between the 6K7G suppressor grid and ground, and your resistor (24) was changed from 700 ohms to 400 ohms. No mention of a change in the capacitor.
The 38-89 schematic confirms: 0.25 uF in parallel with a 400 ohm resistor.
Why yours has a .05 uF cap in place of the 0.25 uF, I do not know. Maybe some long-ago radio repairman had no 0.25 uF caps in stock but had plenty of .05s, so in went the .05, the set worked well enough, so out the door it went?
As for the tube shield bases, that is odd indeed. Most 1937 Philcos have the open clip-type bases, but they started using the 1936 type bases again in 1938. Most likely, Philco had overproduced the 1936 bases and when it was found that ST-type glass octal tube bases would fit in the 1936 bases, they started using them again to restrict usage of tubes to ST-type glass, preventing the use of metal tubes unless the hole was enlarged.
OK. The original Philco 37-89 schematic calls for a 0.25 uF cap in parallel with a 700 ohm resistor from the IF tube cathode to ground.
I checked in the Philco Changes in Models file (available here), and there was a change in Run 5 of the 37-89 where both IF transformers were changed, an extra winding was added between the 6K7G suppressor grid and ground, and your resistor (24) was changed from 700 ohms to 400 ohms. No mention of a change in the capacitor.
The 38-89 schematic confirms: 0.25 uF in parallel with a 400 ohm resistor.
Why yours has a .05 uF cap in place of the 0.25 uF, I do not know. Maybe some long-ago radio repairman had no 0.25 uF caps in stock but had plenty of .05s, so in went the .05, the set worked well enough, so out the door it went?
As for the tube shield bases, that is odd indeed. Most 1937 Philcos have the open clip-type bases, but they started using the 1936 type bases again in 1938. Most likely, Philco had overproduced the 1936 bases and when it was found that ST-type glass octal tube bases would fit in the 1936 bases, they started using them again to restrict usage of tubes to ST-type glass, preventing the use of metal tubes unless the hole was enlarged.
--
Ron Ramirez
Ferdinand IN
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