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

Oscillator problems Zenith 7S-363
#1

I always knew that if I kept playing with radios I would run into an oscillator issue.I’m working on a Zenith 7S-363 that has an oscillator that is deader than three o’clock in the morning.

Schematic can be found here
http://www.nostalgiaair.org/Resources/355/M0025355.htm

I brought this up on another forum and I have tried all the suggestions except substituting a 6J8 tube. That discussion can be found here
https://www.antiqueradios.com/forums/vie...p?t=434443

DC voltages in the radio are mostly on the high side. Voltages on the 6A8 are now as follows; Pin 3 is 323 volts, Pin 4 is 44 volts, pin5 is -0.2 volts, pin 6 is 11 volts,. The voltages shown on the schematic are 235, 30, -1.6 and 190. The voltages shown on the schematic are 235, 30, -1.6 and 190. Measurements were not taken with the specified 1000 ohms per volt meter resistance.

All out of tolerance resistors and all paper caps were replaced. Three different 6A8 tubes were tried and voltages remained approximately the same. Oscillator coil measured 3.1ohms thru the entire lineup of windings and the tickler was about an ohm. Band switch has been cleaned, 6A8 tube socket was replaced due to loose pins,

While I had the tuning condenser out, I pulled the oscillator coil out for inspection and measurements. There were a few dark spots on the coil but it did not look like burn marks, but I could be mistaken, and there was continuity in all coils. I stuck in a generic 455kHz oscillator coil,  still no luck and tube voltages had not changed much.

I used a signal generator to inject a signal that was 455kHz above the stations that I can tune during the day and only the station at 920 lHz could be tuned. Measured the oscillator resonance and found that the oscillator peaked out at 1435 kHz which means the radio cannot tune above 980.

Does anybody have any other ideas I can try before using a substitute tube or possibly rewinding the oscillator coil?

Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it.




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 2554 online users. [Complete List]
» 1 Member(s) | 2553 Guest(s)
Avatar

>