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I finished recapping my 118mx today. When I first fired it up, I wasn't getting any volume, and the low audio I could hear was a garbled and distorted. I fiddled with the volume control and the tuner, and after three or four minutes everything kicked in, the set came to life and played great. I let it play for about an hour and shut it off.
After it had cooled, I cleaned the volume control and went over a few other things. I turned it back on, and same thing happened. Very low volume and distorted sound. Then, slowly, everything clears up and it plays great. It takes about 3-5 minutes for it to start playing well. I don't think it's the volume control because it works great once the set is playing well. Same with the bandswitch.
I've checked voltages and everything looks good. The tubes all test strong. The shadow meter works great as soon as you turn the set on. Any ideas what could cause this problem?
Link to Schematic - http://www.nostalgiaair.org/PagesByModel...013125.pdf
The artist formerly known as Puhpow! 8)
(This post was last modified: 01-08-2014, 05:25 PM by Jamie.)
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1. You are sure your recap was 100%? Including tone control?
2. Tubes testing strong - still if you have substitutes, try to change them one by one. We all know "testing strong" is not 100%. Start with the 42 and 75 . I thought also 6A7 but now that I realized he shadowmeter works, probably not it. But....
3. THis happen in all volume/tone control positions?
(This post was last modified: 01-08-2014, 05:45 PM by morzh.)
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Yes it happens in all volume/tone positions and on both bands too. I recapped everything and went through all of the resistors, one by one. I want this set to be my daily driver, so I've been taking my time.
It's very strange.. garbled audio, poor reception and low volume that slowly gets better over a 5 minute time span. Then the set plays perfect. I will try swapping out tubes, one at a time. It will take a while because I have to allow to set to cool completely or it plays fine.
The artist formerly known as Puhpow! 8)
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Well, also points to a tube if it keeps playing fine after a short turn-off.. The only elements holding the heat there are tubes.
OK, a quicker way:
1. Cool the radio off first. Replace ALL tube at once. If it plays fine, then keep changing untill plays bad. This will not even require you to turn the set off - you can do it hot.
2. If (and I think this is it, a tube) against all expectations it is still the case - try ro replace the speaker. What if it is freezes when cool, and then warms up and something becomes loose when warming up from the field coil? (Not likely).
(This post was last modified: 01-08-2014, 05:52 PM by morzh.)
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Good idea! .I have to scrounge up a lot of tubes..lol I've got about 10 boxes full, and they are not sorted well.
The artist formerly known as Puhpow! 8)
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Morzh, thanks for the help. I've decided to put this off until tomorrow afternoon. I've been standing at my bench, working on the set, all day. I just now noticed that my back is killing me.  For some reason, I never notice my back prolem while I am working on a set, only when I am done. I'll scrounge up the tubes tomorrow afternoon and get back to you.
I did try the set again, and this time, it took 10 minutes for the problem to clear up... so it is getting worse.. something is failing..meanwhile, I touched nothing. I think you hit the nail on the head... it's got to be a tube.
The artist formerly known as Puhpow! 8)
(This post was last modified: 01-08-2014, 06:15 PM by Jamie.)
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Well, standing is a back killer. I have the same thing, my back is normal but if I stand a long time (and mind you - not walk, even with a backpack, but actually stand, like when I cook or am in a museum, or (and I stopped doing that long time ago) accompany my lady in a department store) - my back starts hurting.
But then it is good for you otherwise, so you gotta choose: die from a heart attack but with a good back, or die from something else but with a bad back.
I am still undecided. You know, one could watch his cholesterol and eat plenty of fiber and exercise and then get hit by a bus. And some people I know are still around in their 90s smoking a pack a day.
So I think, I keep sitting at my workplace.
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PuhPow, if your shadow meter is showing a strong signal I would turn my attention to the AF section. If you have a scope I would monitor the control grid of the audio driver and see if you see the change. You could have a flaky interstage transformer. You need to move along to isolate where the signal is reducing.
Good luck, Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Good news! My back is much better today. ..and... the radio is fixed! It was the 42 driver tube. I replaced it, fired up the set and it came on almost instantly. Plays perfect! Morzh, you are the greatest! I hope you are having as good of a day as I am!
The artist formerly known as Puhpow! 8)
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I'd put that bad 42 tube back in to see if the problem comes back.
Sometimes you get fooled.
Chances are that was it!
I will have to remember this one for the future.
Thanks for the saga!
Herb S.
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No need to put it back. You could instantly tell that the problem was solved. With the old 42, the set had no volume, and the low audio was so garbled it sounded like one of those far away shortwave stations you can barely hear. Once I replaced the tube, as soon as I fired it up with the new 42, it came in loud and clear. The chassis is back in the cabinet now and I'm listening to tube talk. 8)
The old tube tests fine on two different testers. So go figure..
The artist formerly known as Puhpow! 8)
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Puhpow,
OK sounds like you've got it then!
I wonder what is going on with the tube then?
Is your tube tester a transconductance measuring type
or just emissions? Did it pass the shorts test and gas test?
Herb S.
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Here she is, all back together. Playing fine, thanks to Mr. Morzh's great advice!
The artist formerly known as Puhpow! 8)
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Beautiful set. My mentor taught me to go left from the speaker until the antenna after all the voltage divider was fixed nd reap/recarb was appropriately done. Served me well all these decades. Recon I would pass this along whilst I still can. So far as I know even Chinese Schmatics follow same, but will try to get answer next week when my non techical GF returns.
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Nice set!
If I could only get my enclosures looking like that!...
I also have been working from the speaker back towards
the antenna. It does make it easier to find problems that
way...
Herb S.
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