A gassy Thankgiving with a 37-650

A gassy Thankgiving with a 37-650 - Printable Version

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A gassy Thankgiving with a 37-650 - raydog - 11-27-2016

Hi all,
Hopefully you took the title tongue and cheek. I like to rotate my consoles every 6-9 months to give them each some playing time and keep them active. My 37-650, has been out of service since May- June sometime. On Thanksgiving morning I went to fire it up and got no sound, nothing, just dial indicator lamp. This evening I decided to dig into it, and what happens is the rectifier (5Y4G) starts to glow a beautiful purple, I hear some audio for about 5 to 10 seconds, then some brighter purple, a little arcing inside the tube , then silence. Am I to assume I need a new recifier tube? The radio was rebuilt by me, about a year ago and was my daily driver for quite a while, and worked well 6 months ago. Just trying to save time in unnecessary troubleshouting as nothing should have been disturbed while it was idle.

Thanks, Don

RE: A gassy Thankgiving with a 37-650 - morzh - 11-27-2016

Doesn't hurt to try.
Other than the socket type, 80 and 5Y4 are the same, and people often have a stock of 80 tubes. You could change the socket or make an adapter.

RE: A gassy Thankgiving with a 37-650 - Phlogiston - 11-27-2016

Assuming that one of your filter caps didn't dry out and short, then yeah, you need a toob.

Favorite gassy tube picture:

RE: A gassy Thankgiving with a 37-650 - raydog - 11-27-2016

Yes I do have some 80s hanging around, but this tube is mounted directly on top of the transformer.

RE: A gassy Thankgiving with a 37-650 - morzh - 11-27-2016

Make an adapter. Use the base of the bad tube as the plug if possible.
Solder, through a plastic pipe , then epoxy together.

RE: A gassy Thankgiving with a 37-650 - Oldresistor47 - 11-28-2016

(11-27-2016, 05:47 PM)raydog Wrote: Hi all,
Hopefully you took the title tongue and cheek. I like to rotate my consoles every 6-9 months to give them each some playing time and keep them active. My 37-650, has been out of service since May- June sometime. On Thanksgiving morning I went to fire it up and got no sound, nothing, just dial indicator lamp. This evening I decided to dig into it, and what happens is the rectifier (5Y4G) starts to glow a beautiful purple, I hear some audio for about 5 to 10 seconds, then some brighter purple, a little arcing inside the tube , then silence. Am I to assume I need a new recifier tube? The radio was rebuilt by me, about a year ago and was my daily driver for quite a while, and worked well 6 months ago. Just trying to save time in unnecessary troubleshouting as nothing should have been disturbed while it was idle.

Thanks, Don

Let me know if the new 5Y4G corrects the problem. Similar circumstances happened to me. I repaired the chassis about 4 months back and I just finished the cabinet. Reinstalled the chassis and now it draws too much current. The 5Y4G has some loose gray flecks floating around but checks good on the tube testor. Has anyone experienced the same problem? I pulled the rectifier and it still draws too much current. I'll double check the transformers winding

RE: A gassy Thankgiving with a 37-650 - Ron Ramirez - 11-28-2016

Check the RF unit. I've had multiple 37-650 RF units experience a failure in the oscillator section; specifically, a burnt carbon track in the band switch section in the oscillator circuit.

I avoid 37-650 sets now for this reason.

RE: A gassy Thankgiving with a 37-650 - Oldresistor47 - 11-28-2016

(11-28-2016, 10:59 PM)Ron Ramirez Wrote: Check the RF unit. I've had multiple 37-650 RF units experience a failure in the oscillator section; specifically, a burnt carbon track in the band switch section in the oscillator circuit.

I avoid 37-650 sets now for this reason.

Thanks Ron. Would not' expectations checked the RF circuit unless you suggested it.

RE: A gassy Thankgiving with a 37-650 - raydog - 11-29-2016

I have a 5Y4GA on order. Thanks Morzh, I can now picture in my head what you are talking about for an adapter. I will do that when I have a chance and use it for further troubleshooting.

I actually got the radio playing last night. The tube glowed purple for maybe a few minutes, then soon dissipated as the radio warmed. I kept it on for over an hour and it played well while keeping a close eye on it. So hopefully this still points to a failing tube.

Ron brought up a good point. A few times I have experienced times where the radio would go silent switching between bands. Rotating the band switch a few times would bring it back to life. Is the carbon track problem repairable? Spray or disassembly?

RE: A gassy Thankgiving with a 37-650 - Ron Ramirez - 11-29-2016

It's repairable...sometimes. I've seen some that had such a bad (and deep) carbon track that I had to discard the unit and find another 37-650 chassis for its RF unit.

I was able to repair one by scraping the carbon out of the burnt track, then using clear epoxy (not J-B Weld, it is conductive) to reinforce the area where I had to scrape carbon out.

Anyway, it requires removal and disassembly of the RF unit.

Thanks a lot, David Grimes. Icon_evil

RE: A gassy Thankgiving with a 37-650 - morzh - 11-29-2016

(11-29-2016, 10:35 AM)Ron Ramirez Wrote: I was able to repair one by scraping the carbon out of the burnt track, then using clear epoxy (not J-B Weld, it is conductive) to reinforce the area where I had to scrape carbon out.

I was about to suggest the same. This is the way I used to repair burnt tracks, scrape and fill with epoxy.

Oh.....and before you replace the tube, test it, first on a tester and then, if passes well, on another radio. Just to make sure it is not the radio that makes the tube glow.

RE: A gassy Thankgiving with a 37-650 - Chris h - 11-30-2016

Is there anything that can or should be done to prevent the carbon tracks from starting in the first place? Like cleaning or treating the socket with something?

I was just wondering, while reading this thread, if I should do anything, proactively, to my 37-116X while I am in there?

RE: A gassy Thankgiving with a 37-650 - Ron Ramirez - 11-30-2016

I don't know why the 37-650 is so prone to this issue, but...

Clean, clean, clean. Get all of that old dust, dirt and grime off the switch wafers while you have the RF unit disassembled. Make sure they are completely dry before applying power.

Other opinions? Feel free to chime in...

RE: A gassy Thankgiving with a 37-650 - morzh - 11-30-2016

Yes. Usually the reason for carbon tracks, other than the fact of a poor design (creepage not sufficient) is the dirt. Clean surface and air are resistant to breakdowns but dirt is less so, so eventually there will be that first spark.