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42-1008 code 122
#31
Hopefully, new resistors will cure the problem!

Next time try 5 watt, minimum. I used 5 and 7 watt resistors to replace the multi-section Candohm "B-C" resistor in my 41-616. So far, so good. Icon_thumbup
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#32
5 watt? Icon_eek

No wonder it smoked. Icon_think

I'm actually surprised it lasted as long as it did.

In the future, I am going to stay away from super small metal film resistors. I would have seen a burned carbon comp much sooner. My eyes ain't what they used to be. Icon_e_geek
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#33
OK, I put in 5W resistors, and the buzz/hum/growl is still there, though with a slightly different sound. It gets much louder when switched to phono.

I took out the audio amp 41 tubes, turned on power and the speaker hums, much louder than a speaker with no audio amplifier feeding into it should. I'm pretty sure the field coil, a part of the filter circuit, shouldn't be this noisy. This all leads me to believe that either the 5Y4G rectifier is weak or the (supposedly) new electrolytic filter caps are leaky. I'm leaning toward the tube because this is a used one I pulled out of my 39-45, which had recently developed a good bit of 60 cycle hum.

Sheesh, I need to invest in a decent tube tester. Icon_idea

I guess I'll just pack this thing up and take it back home with me this weekend. I have a new rectifier tube waiting on me there, anyway.

Of course, feel free to speak up if any of you think I'm wrong. I'm all ears on this thing.
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#34
Well, the new rectifier tube made no difference.

I guess it's time to order new electrolytics.
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#35
I put in new 600V electrolytics and no change. I decided that it was time to do some actual troubleshooting. I know this is a power supply problem because the detector grid is clean and the speaker hums even when the audio output tubes have been removed, which just ain't right. Icon_problem

So I check the transformer winding resistances. All of them look OK.

Then I checked transformer HV secondary output voltages at the rectifier tube pins. Plate voltages to center tap look about right, 345 VAC on either side. I checked filament voltages to ground next. My DMM shows them as 352 VAC on each side and goes kinda wacky when set to DC. Additionally, it's at 60hz, but should be 120hz if the full wave rectifier was working right and the filtering was bad. This really had me scratching my head because it's a NOS rectifier tube that I checked out in my other radio. How can a known good rectifier not be rectifying? Icon_eh

So just to be sure, I checked plate voltages again, but referenced directly to ground this time. First one reads 698 VAC, next one 0VAC. Eureka! Icon_idea

I had spliced on new wires inside the transformer and used heat shrink over the joints. Once the transformer heated a bit, the heat shrink migrated a little on one end of the HV secondary winding, shorting it to ground. Instead of having two legs at about 350VAC, I have one at 700VAC and the other at 0VAC.

I managed to open the clamshell enough to get in there and wrap electrical tape around the entire secondary side, covering all the splices. I put it back together and checked resistances to ground, and it all looks good.

Unfortunately, the largest bias resistor is now open ( Icon_eek it's a five watt, 150 ohm resistor!!!). I don't have one on hand, either.

Oh well, this will have to wait until I can get a replacement resistor. I guess I'll just go back to work on the little Crosley.
It's not how bad you mess up, it's how well you can recover.
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#36
I kinda had a feeling that there was something amiss with that power transformer. When half the fils didn't lite and the fuse blowing issues. Glad you found the stumpper.
Terry
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#37
I'm going to have to pull that transformer out completely to fix it right. But that's OK. It kinda forces me to re-do the bias resistor setup better to prevent future failures.

An ounce of prevention and all that...
It's not how bad you mess up, it's how well you can recover.
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#38
OK, it only took me 5 months to get around to it, but I finally got this thing receiving on-air radio today. Icon_clap

I opened up the power transformer and covered everything up with several wraps of electrical tape, then put it all back together. I checked resistance from every wire to the frame- all good.

I made a new bias resistor network with a short terminal strip and 7 watt resistors.

Plugged it in without tubes just to make sure nothing is going to blow the fuse- no fireworks encountered. Icon_thumbup

Installed the tubes and fired it up. No loud buzzing, so that problem is fixed. Clicked it from SW to BC to Pre-sets to Phono, there's an audible pop from the speaker with each change of input. Turned on the sig gen and fed a signal through a .1mfd cap to the antenna input and checked through the broadcast band and SW band- it makes good audio tone.

Lastly, I connected a homemade antenna to it (stock antenna and cabinet are 12 hours away) and dialed up a few local AM stations. They come in OK, but I'm sure this will need a good alignment. All the presets work, too.

I am darn happy to finally have this thing working again.

Now it's time to tackle the Beam-Of-Light. Icon_idea 8)
It's not how bad you mess up, it's how well you can recover.
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#39
Sweet feeling it is when that eventually happens. Congrats.
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#40
The bad thing about this being my first antique radio to work on and taking so long to do is that I can hardly stand to look at my earlier work on it. There is a discernible learning curve to be seen under the chassis. I'm kinda torn between the urge to rework my uglier early repairs and the overwhelming urge to just bolt it back into the cabinet.

It's my Mother-In-Law's radio though, and she'll be happy with it just working. I guess I'll just leave it be for now and know that there's a strong possibility that I'll be working on it again someday.

Maybe the next radio I do will be an actual restoration instead of a repair.

BTW, thanks again to all for the valuable help and advice along the way. I learned a lot from y'all! Icon_thumbup
It's not how bad you mess up, it's how well you can recover.
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#41
As long as it is safe, no problem.

Then again....how are things between you and your mother in law?
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#42
Finally, the chassis and cabinet have been reunited. I did a good alignment with the antenna attached and it works better than expected. There are a few stations that aren't even local coming in during the day time, but we are on a mountain and overlooking the Tennessee River Valley.
It's not how bad you mess up, it's how well you can recover.
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#43
What ohms of resistors did you use? We’re they the original 14, 15, and 146 or did you round up?
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#44
Hi and welcome to the Phorum,
If you are seeking a specific answer from Eric he hasn't visited the Phorum in over a year. The general answer to your question is that round a bit is ok. The voltages are not super critical. If you used a pair of 15 ohm resistor and a 150 ohm resistor you'll be fine.
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow

Terry
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#45
Thanks.
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