37-38 Purpose of Resistor 40 - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: 37-38 Purpose of Resistor 40 (/showthread.php?tid=5120)

---

37-38 Purpose of Resistor 40 - davemc - 08-24-2012

http://www.nostalgiaair.org/PagesByModel/204/M0013204.pdf
Anyone know the purpose of resistor 40 in the Philco 37-38? It appears to simply place a 10ma load on the C-9 battery! I see no other purpose. When the switch is ON, C+ is connected to the chassis ground, and C-9 is connected through the switch to resistor 40 (unless I am missing something!)

Was this to help sell Philco batteries? It certainly complicates powering this set from the usual ABC battery eliminator! When I restored my set, I had to build a separate C supply for C-9, and used my AES K-101A to provide the C-3 and the rest of the voltages.

Thanks!

---

RE: 37-38 Purpose of Resistor 40 - Chuck Schwark - 08-24-2012

Resistor 40 and 34 form a voltage divider for the audio grid bias voltage.

---

RE: 37-38 Purpose of Resistor 40 - davemc - 08-25-2012

Thanks, but I still don't get it. There should be NO current flowing through resistor 34, since the 1H4 driver is operating in class A. So the grid voltage on the 1H4 should be -9 volts (it will be less if measured by a DVM or VTVM since even a 10meg input resistance will pull it down). I don't see how resistor 40 would affect that voltage in any way (other than running down the battery prematurely!)

---