37-89 part value question - Printable Version
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37-89 part value question - LASJayhawk - 11-04-2012
Wondering about the values of C22 and R24. The schematic I have shows a .25 uf and 700 ohms. The chassis I have has a .05 uf and a micamold resistor of unknown value.
FWIW: the RF deck has the 37 style tube shield base, the main chassis has the 36/38/39 style on it. Thought that was interesting.
RE: 37-89 part value question - LASJayhawk - 11-10-2012
anyone? is cold dark and lonely in this thread.
I looked at some other 37's and phound philco was all over the map on the 6K7G IF's Many have the cathode straight to ground but some other variations are:
37-602 300 ohms and 0.05 uF
37-604 300 ohms and 0.1 uF
37-620 400 0hms and 0.05 uF (37-630 also)
37-640 700 ohms and 0.25 uF
These are per the Riders prints in book 7
Was Philco Playing with the IF gain for fun or what????
And in a Philco wouldn't it be a IPH?
RE: 37-89 part value question - Ron Ramirez - 11-11-2012
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.
RE: 37-89 part value question - LASJayhawk - 11-12-2012
Well i checked and the resistor (a micamold) is 700 Ohms and I have the early IF transformers. The workmanship on the 0.05 is too good to be anything but factory and the end that goes to the chassis lead is under the leads for the 2 mica caps, so I'm going to now assume a factory error. It's pretty twitchy about the adjustment of the 1st IF transformer, it will be interesting to see if changing to a .25 uF improves that.
Whats really strange about the set, the rubber in the dial lamp is as good as the day it was made, and the grill cloth is a little dirty but has no damage at all.
Lil thing plays pretty good too.
RE: 37-89 part value question - LASJayhawk - 11-20-2012
Ok I'll pass this on. I still have the 0.05 uF in there, too lazy to change it.
But I DID find out why the 1st IF transformer adjustment was so ticklish, R16 (1000 ohms, 1/2 watt) had drifted town to about 370 ohms. Replacing the resistor fixed that.
I like the odd stuff, makes it a Phreak Philco.