Need help with GE HJ-618 AC radio/phonograph

BTW- Do you know the difference between freeze spray and air duster? (Besides the $$).
 It is the length of the tube in the can.
 To turn air duster into freeze or vice versa, just invert the can!!

Thats great!
Sometime its just a little thing that causes headaches.
Most radio's were assembled in a hurry up fashion, and maybe the assembly line inspector wasn't doing His or Her Job.
The thing that's most important after Parts failure is connection and switch contacts.

Happy Christmas

Thanks Frank and Cliff, I'm happy to say that the freeze spray found it.  There was a poor solder joint on a tie strip where I replaced a resistor.  Somehow I don't think of solder joints going south when warm, but when the spray got rid of the hum twice, I knew I'd found the problem.  The tie strip is between the volume control and the grid cap of the 6Q7 with 2 stages of amplification after it, so there was plenty of opportunity for the set to pick up EMI.  I have it back together and playing Christmas music from our local AM station as I type this.  The radio's phonograph section is working perfectly as well.  It's never sounded better.  I know *I* will have a merry Christmas!
 
Best regards,
Joel

Interesting that the problem can be cured by pushing on the IF can...

 I would suggest resoldering all the ground connections, and if the filters were replaced as a can, resolder that connection.
 Also tighten up any IFT and tube socket mounting screws, as well as any control grounds.
  Intermittents are the worst  things to track down. 
I would wonder if one of the filter cap leads was failing inside the cap can.

Do you have a scope or can borrow one? That and an isolation transformer would readily track the problem down.

Thanks for the link to the article; lots of info there.  My turntable drive is simpler with only one idler wheel, and looks just like the one in a Zenith unit I had previously - probably later production.  It occurred to me after I sent my OP that lthough the chassis had been recapped, because it looked old I replaced the dual-section filter cap with a unit I bought 8-10 years ago.  I thought that just maybe the replacement has problems, so this evening I replaced it with individual caps.  In the time I've played it since, it's been fine.  I will cross my fingers and give it a long run tomorrow.

I'm preparing myself for it to play fine for 2 hours when disassembled, and then go south when it's back together.   If that happens I will look for cold solder joints and the like. Pretty sure it's not a cable problem.  Curiously, today (but not yesterday) I could "fix" the problem by turning the set off and right back on.  And even more curiously, today I could cause the problem by simply touching one of the IF transformer cans.  This set is a real looker though, so I'll stick with it until I solve the problem.

If you hear a buzz, you may have an audio cable that is bad. 

You could have a ground wire that maybe has a cold solder joint.
 or an open wire. 

Here's some information, Whether it's helpful or not I don't know.
GE HJ-618 AC radio/phonograph

There are any number of ham radio clubs in your area where you could contact, or go on the web and look for Audio Clubs or phone graph clubs.

Greetings, everyone!  I'm very glad I found this forum.  I have a GE HJ-618 AC radio/phonograph that I bought a few years ago, sold to me as restored.  It worked fine for awhile, but then the phonograph quit, so I put the set on my bench.  The problem was in the phono cartridge, which supposedly had been rebuilt but I had to have it rebuilt again.  While I had the chassis out I noted that it had been recapped.  I went ahead and replaced all the resistors as many were out of tolerance.  When I got the cartridge back I reassembled the set and it sounded great.  After about 10-15 minutes it developed a loud buzz that doesn't vary with the volume control.  I tried replacing the tubes one by one, and the buzz is still there.  If I turn the set off and let it cool for awhile, it plays fine but the buzz returns after it's warm.  I ordered freeze spray but I don't know what component(s) could be at fault that haven't already been replaced.

If it matters, the chassis is AC/DC with 6SA7/6SK7/6Q7/6J5/25L6/25Z6 plus a ballast tube.  I will greatly appreciate any advice/suggestions, as I have a bunch of 78 RP Christmas records I'd like to play.

Thanks!