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

Zenith 7H920 AM but no FM
#1

OK, here's my latest project. I replaced all electrolytics and wax/paper caps. Checked and replaced all resistors. Checked all coils. All tube test good.
AM sounds great. FM just hums. While turning the dial, I was able to disrupt reception on an FM radio on my bench. So I guess the oscillator is working. I checked the AM/FM switch (had a problem with one on a Philco once) and it appears to be OK. Any ideas where to look?
Here's the schematic: http://www.nostalgiaair.org/Resources/312/M0025312.htm

Thanks,
Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org

#2

Before any of the below is considered, you may want to clean all the tube pins and sockets by using DeOxit or similar and rocking the tubes a bit in the sockets. FM is very picky about signal path.

My first suspect would be the 19T8. These have in my experience a very high H-K leakage failure rate. If you have a scope and an isolation transformer, I would trace the signal beginning at the input to the 1st IF and go downstream from there until you lose it. If it's not there at the 1st IF, then you may need to replace the 12AT7.
#3

Thanks. I'll check this out and get back to you.

Eric

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org





Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
trying to identify this wire type
The red wire is rubber covered wire. The others are cotton braid over rubber often in colors or a tracer, also strand...Chas — 02:43 PM
trying to identify this wire type
Greetings Phorum members, Hope you can help me identify this type of wire in the photo I have attached.  I am not sure ...georgetownjohn — 01:53 PM
Philco 60 Squealing
All correct shields must be in place, all tubes correct no subs of any kind. Check any soldered, riveted ground conne...Chas — 01:24 PM
Philco 60 Squealing
I have recapped and replaced out of tolerance resistors and so on. Radio plays nicely on fairly strong stations. The pro...dconant — 10:55 AM
Philco 46-420 Code 121 Reception issues
Welcome Eric, I agree with Bob and far as the two main electrolytic filter capacitors did you change them yourself or w...radiorich — 11:43 PM
Philco 46-420 Code 121 Reception issues
You mentioned the Philco manual and going through the check points...just to be sure we're on the same page here's the m...klondike98 — 08:13 PM
Philco 42-1008 conversion kit
Interesting. I haven't seen that before.klondike98 — 07:02 PM
12' Philco
Yes I had looked for it on the web as well some time back and could not find it. I was glad to see it turned up in Ron'...klondike98 — 06:59 PM
Shadow Meter Bulb
Now if you had a set with a tuning light then the bulb type is important to the circuit, some sets used those prior to t...Arran — 04:58 PM
Shadow Meter Bulb
Ok. Thanks for the correction.RossH — 03:09 PM

[-]
Who's Online
There are currently 4163 online users. [Complete List]
» 1 Member(s) | 4162 Guest(s)
Avatar

>