FM weirdness from my H723

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FM weirdness from my H723

Post by beebs on Tue Feb 24, 2009 2:44 am

Hey all, been scratching my head about this for a few days, and today just put the icing on the cake. When I first got this radio, I played it for several hours (it was reworked by the seller) and noticed that the stations would "drift" on the FM side of things after the radio had warmed up for about an hour...my favorite classical station at 89.5 would suddenly static out and I'd move the dial up to above 90 to about 92, and it would "reappear" again. The station usually at 107.1 suddenly moved to around 108, etc. It would shift several times before "settling in"...wrote the seller and he said that "pre-AFC" FM radios just "did that," that being one of the reasons AFC was such a big deal.

OK, I thought, a little inconvenient but it still worked. Ended up having to retune "up" every time I ran the radio for more than an hour. Then a few days ago, I turned it on and the entire FM band was just fuzzy. I went the whole range of the dial, and got what sounded like one or two stations "spread out" over the whole dial, very "unfocused" and fuzzy, like one station occupied from say 92 up to 98 on the dial, but not really coming in clearly at all. Stayed that way for the next two or three days, whenever I would try it. Turned it off and got busy with other things, forgot about it for a coupla days. Listened to the AM side a couple of times in that interim, and that worked...picked up 86 KONO in San Antonio, one of those stations I remembered from childhood, just fine. Today, I thought I'd just try the FM side again to see what it would do, and it worked...perfectly. And the stations had "shifted" back down to where they should have been on the dial to begin with. I didn't listen for long, just shut it back down after making sure I wasn't imagining that it really was working again.

Anybody know what sorta gremlins might be causing this strangeness on the FM? Should I call "Ghost Hunters"?

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Re: FM weirdness from my H723

Post by Naddy69 on Wed Feb 25, 2009 7:53 pm

Well, FM absolutely will drift on a tube radio without AFC. I have an Emud (German) radio without AFC and I don't use it for FM for this very reason. The AM side works fine and sounds great.

As for your other issue, I have no idea. Could be a bad connection somewhere. I would try poking around while the set is on with a plastic or wood object of some kind and see if anything pops up.

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Re: FM weirdness from my H723

Post by beebs on Wed Feb 25, 2009 10:01 pm

Thanks Naddy69. I have had it playing most of the day today, and it has drifted some, but settled in, just like it did when I first played it. Nice little set, but the 825s w/AFC and the bigger speaker do kinda show it up. I'll poke around in it this weekend and see what I can find.

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Re: FM weirdness from my H723

Post by exray on Wed Feb 25, 2009 10:32 pm

beebs wrote:.my favorite classical station at 89.5 would suddenly static out and I'd move the dial up to above 90 to about 92, and it would "reappear" again. The station usually at 107.1 suddenly moved to around 108, etc. It would shift several times before "settling in"...wrote the seller and he said that "pre-AFC" FM radios just "did that," that being one of the reasons AFC was such a big deal.

Jumping and drifting are two different issues. I forget if that model uses a typical tuning cap or slug tuned coils. If its a cap then try cleaning the wiper contact from the rotor to the frame. Also clean the pins on the oscillator tube and socket.
That should cure the jumping...the drift will remain but will not be so dramatic as a megahertz or two.
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Re: FM weirdness from my H723

Post by beebs on Wed Feb 25, 2009 10:44 pm

Thanks for that, exray. I'll hit it with DeOxit and see if that makes a difference.

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Re: FM weirdness from my H723

Post by exray on Wed Feb 25, 2009 11:06 pm

Use it sparingly! Too much of a good thing can soak into the socket and kill the FM completely, ya know.

What I do is spray a bit on the pins of the tube and then work the tube in and out of the socket a few times.

On the cap wiper (if that applies) just spray enough on the end of a small screwdriver to develop a droplet that you can place exactly where you want it.
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Re: FM weirdness from my H723

Post by beebs on Wed Feb 25, 2009 11:33 pm

Roger that...I've got the small plastic squeeze bottle of it, the one with the needle delivery tube. Only puts out a tiny drop at a time.

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Re: FM weirdness from my H723

Post by exray on Wed Feb 25, 2009 11:41 pm

Good man!
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Re: FM weirdness from my H723

Post by RadioRich on Thu Feb 26, 2009 3:13 am

Beebs,
Wow thats a strange one well I figure xray to come back with answer like Siler mica
Disease.
Sincerely Rich

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Re: FM weirdness from my H723

Post by exray on Thu Feb 26, 2009 7:58 am

Being an H723 thats a potential issue, Rich, but it won't cause the jumping and drifting Wink
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Re: FM weirdness from my H723

Post by Bill Cahill on Thu Feb 26, 2009 1:44 pm

More likely cause poor, or, no reception at all.
Check your switches. Sounds like dirty switches to me.
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Re: FM weirdness from my H723

Post by beebs on Thu Feb 26, 2009 11:37 pm

Actually, the switch for AM/FM seems to have some personality problems...sometimes it doesn't seem like it makes the click all the way. So I'll be checking that, too.

After about an hour of playing hide-and-seek with the station, the radio played beautifully all day yesterday. Turned it on at about 9:30 am, and it "settled in" at about 11:00 am. Stayed solid the rest of the day. We finally turned it off about 10:30 last night.

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Re: FM weirdness from my H723

Post by beebs on Thu Mar 05, 2009 11:42 am

Well, I actually DID get to dig into it this past weekend, been busy ever since, and have been trying to upload a video of it to youtube for the last three days...finally got THAT to work last night...the radio works great! I took it apart and cleaned the tube pins and the sockets with a tiny drop of Deoxit on each, and used a tiny screwdriver and paper towels to get the residue off. Also cleaned some gunge from what contacts in the bandswitch that I could get to...bandswitch definitely "clicks" better than before. After about fifteen minutes of reasonable "drift" the fade-out thing happened, but then it came right back, and has been rock-solid ever since. I'm wondering if it has anything to do with moisture or humidity in some of the old parts? At any rate, it works fine now, and sounds great, a big thanks to all for their suggestions of what to do. Here's the link to the little demo video I made of it. I am going to post a webpage with pics for it, as well. I'll add that link when I get it done. Here's the youtube address:

http://www.youtube.com/watch?v=u-ciLhnbGJU

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Re: FM weirdness from my H723

Post by Timaaay! on Thu Mar 05, 2009 1:18 pm

Glad it worked out for you. The old Zenith sounds great! It's always an awesome feeling to bring a radio back from the brink, isn't it? I like the video! I should do some with my sets too.
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Re: FM weirdness from my H723

Post by beebs on Fri Mar 06, 2009 12:20 pm

Thanks! I'm trying to get the hang of this video thing. Figured I'd go through the collection and do a little demo of each radio. Got another one put up last night.

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Re: FM weirdness from my H723

Post by Don Cavey on Sun Mar 08, 2009 9:34 pm

Glad that you got it going. I have another Zenith, forget the number, and it too plays just fine. (And it is all original, even the filter) Just have not gotten to it yet. They made good radios...

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