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

Philco 38-690 Oscillator Not Working?
#1

I have strong audio signals and strong IF signals. I am receiving no stations at all.

The local oscillator does not seem to be working. Oscillator voltages are as follows:
Pin 3 - 191.8 VDC
Pin 4 - 93.0 VDC
Pin 5 - 1.58 VDC
Pin 6 - 195.5 VDC
Pin 8 - 2.53 VDC
Grid Cap - 0 VDC

The mixer voltages are as follows:
Pin 3 - 238.1 VDC
Pin 4 - 99.7 VDC
Pin 5 - 1.58 VDC
Pin 6 - 99.7 VDC
Pin 8 2.53 VDC
Grid Cap - 0 VDC

Shouldn't the pin 5 of the oscillator grid measure a large negative voltage? Does the OSC CONT tube
have control over the oscillator?

Thanks for any suggestions and help.
nv3g
Oscar
#2

>Shouldn't the pin 5 of the oscillator grid measure a large negative voltage?

I wound think so also the control grid of the mixer too as they wired together.

If you are not seeing any -voltage there you may want to check the normal suspects. These being a dirty band switch, weak 6A8, or bent plate on the osc section on the tuning cap. Did you replace ALL of the foil paper caps in the sub chassis? A missed one could kill the osc. If you removed the sub chassis is it wired in properly?

>Does the OSC CONT tube have control over the oscillator?

Yes it does via the magnet tuning circuit. Don't think that it would stop the osc from working.

When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!

Terry




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
HiFi (Chifi) tube amp build - but my own design.
Tim, nice write up and thanks for sharing !! Sincerely Richardradiorich — 02:47 AM
HiFi (Chifi) tube amp build - but my own design.
Well, this was a real "Hum-Dinger" :lol: ! This will be kinda long, but hopefully it will help others having t...TV MAN — 01:55 AM
Shadow Meter Bulb
Phorum members, I am trying to find the bulb # for PHILCO Shadow Meter part number 45-2180 that is from a 37-640 chassis...georgetownjohn — 06:53 PM
Philco 41-608 changer coupler
3D-printing...short of machining, of course. Or molding.morzh — 05:20 PM
Philco 41-608 changer coupler
Thanks, Morzh. That solves the issue of the rubber pieces. Now, I need to find a way to replicate the pot metal piec...alangard — 05:07 PM
12' Philco
If it is 12', either Kareem or Andre would have to jump pretty high to look at the front panel. Kareem would have an e...morzh — 01:48 PM
12' Philco
And here's a story about the tires on the truck. Same "no-stoop" guy must have installed these! Take care a...GarySP — 01:17 PM
Hickok AC51 tube tester
I think they have only shown the secondaries of the transformer. Two of them feed the rectifiers' filaments.morzh — 12:58 PM
IF can wire size and Rubber mounts?
Arran If the wire inside cans is the gauges you mentioned, the sole reason for that would be mechanical, to stiffen t...morzh — 12:56 PM
12' Philco
Rod, Yes, I know, but the Giant Philco is not around anymore either, so I go by whoever was alive fairly recently. H...morzh — 12:54 PM

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

>