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1965 Calrad tube tuner (model 202M) signal cutting out

Moonwatcher

Moonwatcher

Active Member
Hello, all. This Calrad tuner has been working perfectly, but suddenly the sound is cutting in and out and then completely out. It usually sounds great for five or ten minutes, then it just goes silent and the signal strength meter shows no life. Most all of the tubes seem to be lit, but I was wondering if there might be a likely culprit--a particular cap or tube, maybe. I notice there is one valve that may not be lit (circled in final photo).

Intermittently, a signal might come through for a second, then it goes quiet. Fiddling with the antenna connection sometimes leads to a couple of fleeting moments of static. I don’t know much about working with tubes (besides how to pay too much for them!). Photos are below.

Thank you so much for any thoughts you might have!
 

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I would try the replacing the front-end tubes, with new nor NOS tubes. Often tube will test good statically on the tester, but not while at RF frequencies.
 
It looks like the tube you have circled is in an IF stage. There are usually more than one of the same type, so swap it with another of the same type. Sometimes old tube pins and sockets get contaminated and just moving the tubes around in their sockets will result in the unit operating. Contact cleaner is a necessity when you are working on old equipment like this. It may also pay to use contact cleaner on the selector switch. There may be years of tar and nicotine on the contacts from when most people smoked. The tube you show as not lit will most likely have pins 3 and 4 as heater pins. You can check for resistance between them.which will likely be on the order of 5 ohms cold and 21 ohms hot. I just measured a similar tube and it was 4.6 ohms cold.
 
That is
Punker X said:
I would try the replacing the front-end tubes, with new nor NOS tubes. Often tube will test good statically on the tester, but not while at RF frequencies.
Click to expand...
a great idea
Punker X said:
I would try the replacing the front-end tubes, with new nor NOS tubes. Often tube will test good statically on the tester, but not while at RF frequencies.
Click to expand...

Great idea--I hope I can ID that tube. Thanks!
 
Great idea--I hope I can ID the tube. There may be a schematic floating around somewhere in cyberspace. Thanks!
Punker X said:
I would try the replacing the front-end tubes, with new nor NOS tubes. Often tube will test good statically on the tester, but not while at RF frequencies.[/QUOT
Click to expand...
 
amptramp said:
It looks like the tube you have circled is in an IF stage. There are usually more than one of the same type, so swap it with another of the same type. Sometimes old tube pins and sockets get contaminated and just moving the tubes around in their sockets will result in the unit operating. Contact cleaner is a necessity when you are working on old equipment like this. It may also pay to use contact cleaner on the selector switch. There may be years of tar and nicotine on the contacts from when most people smoked. The tube you show as not lit will most likely have pins 3 and 4 as heater pins. You can check for resistance between them.which will likely be on the order of 5 ohms cold and 21 ohms hot. I just measured a similar tube and it was 4.6 ohms cold.
Click to expand...

Why I haven't already done that I don't know. But yes, I will clean all the pins and sockets and report back. Thanks!
 
Thanks for all your responses, everybody. Looks like a case of great minds think alike! Thank you! :bowdown:
 
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Silver mica disease doesn't usually switch things on and off, it usually sounds like a lightning storm in the signal. You may have silver mica disease eventually but you haven't given evidence of it yet. Silver mica disease is caused by silver migrating under the influence of voltage to where it shorts out the capacitor momentarily as the short blows clear. Eventually it gets permanent.
 
Hmm, thanks. Silver mica disease sounds scary. But it isn't loud when the sound goes on or off.

Okay, so I used contact cleaner on all the pins and in all the tube jacks, and there is no change. It sounds great for ten minutes or so and then cuts out. If I leave it on, the sound comes back for a few minutes--and sounds great- and then it cuts out. The next step should be to start substituting other tubes.

WAIT! . . . even as I write this, perfect sound has come back and hasn't cut out in a half hour!:banana::banana::banana:

I will leave it on to see if it continues to work. If so, I sure won't look a gift horse in its silver mica fillings!:rflmao:

Anyway, thanks everyone for offering such helpful information.

UH-OH . . . now it's gone off again and come back on with static. And now it's playing well and now static and now . . . :wtf:

So back to trying tube substitution, and maybe I can find something to measure the ohms between pins. If this kind of intermittent performance resonates with anyone, please let me know. Thanks again for sharing your expertise.
 
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give the tubes a wobble next time it cuts out and see if it pops back to life. Might still be crusty, or a broken solder joint

I have had dying oscillator tubes that would get warm and just stop working, and other tubes that would slowly fade out as they ran. My console stereo actually has that issue currently, it works really well cold but by the time its been on an hour it only pulls in the strongest stations. Need to pull it out and see what ails it. Its been pretty far down on the list of things to fool with.
 
gadget73 said:
give the tubes a wobble next time it cuts out and see if it pops back to life. Might still be crusty, or a broken solder joint

I have had dying oscillator tubes that would get warm and just stop working, and other tubes that would slowly fade out as they ran. My console stereo actually has that issue currently, it works really well cold but by the time its been on an hour it only pulls in the strongest stations. Need to pull it out and see what ails it. Its been pretty far down on the list of things to fool with.
Click to expand...

Yeah, thanks. The more things you scratch off the list the longer it gets--a law of the universe I will never understand. But back to tubes, I've wobbled them, removed them and sprayed pins with contact cleaner, etc. I'm not sure at this point how to access solder joints, but I will investigate.
 
flip it over and take the bottom off.

Had a Sherwood that would cut in and out, broken solder joint on one of the coils in the front end under the main tuning condenser. Turning the dial would flex things just enough to make or break the connection.

lots of dumb things can happen with tuners, especially old ones, and any number of them can kill the whole works.
 
Breakthrough! I was trying all kinds of things and noticed, while jiggling the two ECC85 tubes directly behind the antenna connection, that the problem would come and go. I thought it was the tubes and found another pair, but as I was changing them out I noticed a pin on one of them was badly bent into its neighbor. So I straightened it out as best I could and replaced it in the socket, and that seems to have solved the problem. I've been listening several hours and it hasn't cut out!

Thanks to everybody, especially Gadget73 and Punker X, who had me focusing on the pins and the tubes on the front end (I had to look up front end). I always learn something on this site.
 
Moonwatcher said:
Breakthrough! I was trying all kinds of things and noticed, while jiggling the two ECC85 tubes directly behind the antenna connection, that the problem would come and go. I thought it was the tubes and found another pair, but as I was changing them out I noticed a pin on one of them was badly bent into its neighbor. So I straightened it out as best I could and replaced it in the socket, and that seems to have solved the problem. I've been listening several hours and it hasn't cut out!

Love seeing this post. You learned a lot about troubleshooting. And you got it working. Enjoyed your solution to your problem.

Thanks to everybody, especially Gadget73 and Punker X, who had me focusing on the pins and the tubes on the front end (I had to look up front end). I always learn something on this site.
Click to expand...
 
I appreciate your appreciation, Kent. In retrospect, I don't understand how I could have removed every tube and cleaned it and still missed that bent pin. But the unit is actually sounding better than ever, thanks to upgrading a couple of tubes in the process of all this. And station drift, which had been a problem, has largely subsided.
 
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