Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Philco 20 voltages
#30

So I played with the bias on the detector by dropping the cathode resistor to under 10K ohms. This brought the plate voltage down to about 75 volts, but I started to pick up distortion. I presume the tube reached very close to full saturation. No way I can figure how they got the 35 volts unless their 1000ohms/volt meter drags it down that far... It doesn't! I dug out an old VOM and it dropped the plate voltage only about 6 volts.

Chris, the grid is at ground potential. Coil is very low resistance. About 4 ohms. There is some current as the drop across the two plate resistors is about 20 volts. Not fully at cutoff.

For grins and giggles I hooked up the scope to the detector grid and plate. On the grid, with a strong AM signal, I got about 800mv modulated RF with the probe set to 10/1. Even this reduced the volume quite a bit. On the plate with the probe sill at 10/1, I get about 200 mv of RF, and almost 4 volts of AF. No reduction in audio volume with the probe connected to the plate, as would be expected.

Patrick, make sure your coils are good. I know mine measured ok, but there was a lot of green corrosion due to the dreaded Philco coil disease. I just decided to rewind them to be sure. Only the outside winding needs to be replaced.

Rob


Messages In This Thread
Philco 20 voltages - by Patrick - 02-26-2021, 11:41 AM
RE: Philco 20 voltages - by Radioroslyn - 02-26-2021, 01:22 PM
RE: Philco 20 voltages - by Patrick - 02-27-2021, 08:29 AM
RE: Philco 20 voltages - by Radioroslyn - 02-27-2021, 09:58 AM
RE: Philco 20 voltages - by RodB - 02-27-2021, 11:20 AM
RE: Philco 20 voltages - by 462ron - 02-27-2021, 11:28 AM
RE: Philco 20 voltages - by rfeenstra - 02-27-2021, 01:20 PM
RE: Philco 20 voltages - by Radioroslyn - 02-27-2021, 01:34 PM
RE: Philco 20 voltages - by 462ron - 02-27-2021, 01:45 PM
RE: Philco 20 voltages - by Patrick - 02-27-2021, 03:38 PM
RE: Philco 20 voltages - by RodB - 02-27-2021, 08:25 PM
RE: Philco 20 voltages - by RodB - 02-27-2021, 09:14 PM
RE: Philco 20 voltages - by Patrick - 02-27-2021, 09:57 PM
RE: Philco 20 voltages - by radio1 - 02-27-2021, 10:11 PM
RE: Philco 20 voltages - by rfeenstra - 02-28-2021, 01:16 AM
RE: Philco 20 voltages - by Patrick - 02-28-2021, 06:46 AM
RE: Philco 20 voltages - by Radioroslyn - 02-28-2021, 07:41 AM
RE: Philco 20 voltages - by Radioroslyn - 02-28-2021, 09:46 AM
RE: Philco 20 voltages - by Bill Bacco - 02-28-2021, 09:56 AM
RE: Philco 20 voltages - by Patrick - 02-28-2021, 11:25 AM
RE: Philco 20 voltages - by Patrick - 02-28-2021, 11:32 AM
RE: Philco 20 voltages - by Patrick - 02-28-2021, 12:03 PM
RE: Philco 20 voltages - by OZ4 - 02-28-2021, 03:06 PM
RE: Philco 20 voltages - by radiohenry - 02-28-2021, 05:11 PM
RE: Philco 20 voltages - by Patrick - 02-28-2021, 05:17 PM
RE: Philco 20 voltages - by radiohenry - 02-28-2021, 05:23 PM
RE: Philco 20 voltages - by OZ4 - 02-28-2021, 10:11 PM
RE: Philco 20 voltages - by rfeenstra - 02-28-2021, 10:33 PM
RE: Philco 20 voltages - by OZ4 - 02-28-2021, 10:42 PM
RE: Philco 20 voltages - by rfeenstra - 02-28-2021, 11:49 PM
RE: Philco 20 voltages - by Patrick - 03-01-2021, 06:19 AM
RE: Philco 20 voltages - by Patrick - 03-14-2021, 09:22 PM
RE: Philco 20 voltages - by morzh - 03-14-2021, 10:47 PM
RE: Philco 20 voltages - by Patrick - 03-15-2021, 06:15 AM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco 42-345 Restoration/Repair
Today I've been reading through the site trying to learn more about this radio. I also soldered the lose power cord cabl...osanders0311 — 08:24 PM
Philco 610B oscillator wiring
Thanks David! I do have that same later prodution model 610 schematic. I've also studied the Philco service bulletins fo...Tubester — 08:12 PM
Philco 610B oscillator wiring
Some info from Beitmans says late production. David   David — 06:06 PM
Restoring Philco 96
Oh wow! Just found this thread.  Brings me back to early days on this phorum.  I did a 96 back in 2017.  Thread here: ...rfeenstra — 06:05 PM
Philco 610B oscillator wiring
Thanks for the replies. It's not the really the hum that I am after. Just trying to understand why only the shortwave ba...Tubester — 04:01 PM
Restoring Philco 96
70 and 90 are Superhets, but at least the 2x45 model of 90 uses the Plate detector (and so does 70). Also the Atwaters,...morzh — 03:28 PM
Restoring Philco 96
Morzh, Prayers for your mom. I am sure that there was enough pain living through the Holocaust as a child. I pray dail...MrFixr55 — 02:19 PM
Philco 610B oscillator wiring
Hi Dan, Divide and conquer. First off trry to differentiate between 60Hz and 120 Hz hum. 120 Hz hum has a higher pit...MrFixr55 — 01:49 PM
Restoring Philco 96
Yes, other than takin a toll on your back, they are undeed way more repair friendly than many other Philcos. To me, som...morzh — 01:04 PM
Philco 610B oscillator wiring
If the wires look like they were this way from the factory (very neat and very dull soldering joints), I'd leave them be...morzh — 12:58 PM

[-]
Who's Online
There are currently no members online.

>