Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

1939 model 39-30
#1

Just finished restoring this. It took three #75 tubes until I found a good one that didn't cause a muffled hissing after the set played for about 5 or 10 minutes. As soon as you'd just touch the top of the cap on the tube, the hissing would cease. It looks a lot more shiny than it really is. The flash made it look too glossy. I had just applied a coat of Liquid Gold spray to the cabinet, and the excess that didn't wipe off hadn't dried yet.

   
   
   
   

Greg V.
West Bend, WI
Member WARCI.org
#2

Nice Job! Look lke an eastern set, most of those stations I can get over here. WCAU is WPHT now as of 10 or so years ago. I don't understand why stations change call signs after many many years. Kinda like us hams the FCC has allowed us the to have call signs which don't necessarily have to be in the call district we are in. It's a bit of annoyance you think the guy is in Calf. but he's next door.
Terry
#3

Any stray capacitance between the 75 grid cap and the plate of the output tube ( 41, 42, etc.) can cause hi freq audio oscillation. Dress the grid lead away and/or try some shielding.
#4

Beautiful radio. Great job!

The artist formerly known as Puhpow! 8)
#5

I've got a 39-30 as well. I have seen some 39-30's with only 1 tube shield, on the 75 tube. For whatever reason, my radio has provisions for two tube shields, on the 75 and the 37. But, when I got it, it only came with only 1 actual tube shield installed, on the 75. Could that be part of your problem?

Tom
#6

Bill/Tom: great advice. Funny thing about 75 tubes, the mutual conductance of the triode is only 750 uMhos, and it doesn't take long for it to degrade to the 500 range. In sets where the 75 is the only AF amp before the output tube this can be an issue.

Also: 42 tubes can be noisy after they warm up. Same goes for 6F6 tubes.
#7

OH YES, very nice job on you set!! Icon_thumbupIcon_thumbupIcon_clap
#8

Mine only has one tube shield too over the 75 tube.

Greg V.
West Bend, WI
Member WARCI.org
#9

Quote:It took three #75 tubes until I found a good one that didn't cause a muffled hissing after the set played for about 5 or 10 minutes

That might have been a supersonic parasitic oscillation. A "grid stopper" resistor, around 68K, placed in series with the grid wire right at the top cap of this tube (its grid), should tame those unruly tubes you have. This resistor, in combination with the tube's stray capacitance, acts like a low pass filter to disable the oscillation.
#10

Real nice looking set--great restoration !
#11

Thanks, everyone. The set is working fine now. I think it had a lot to do with shielding around that 75 tube. No more muffled hissing. Icon_thumbup

Greg V.
West Bend, WI
Member WARCI.org
#12

I really like the rear lighted dial on these 1939's. And, using the "Rebuilding Philco Pilot Lamps" tip found in the tech section ( http://philcoradio.com/tech/lamps.htm ) it no longer flickers on and off! Icon_lol

Greg V.
West Bend, WI
Member WARCI.org
#13

Still love those wine flavored buttons! Icon_e_biggrin
#14

Another thing to watch for on a 75 tube, or any other glass tube with a grid cap, is the solder joint on the grid cap giving out. Also the clip on the end of the grid lead can have problems, the solder joint going bad or the wire breaking internally.
Regards
Arran
#15

Wow. Really great restoration!Icon_clapIcon_clap

Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org





Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Jackson 715 not working
Now that you posted the schematic, I don't know why that Sprague electrolytic cap is across the meter, as it is not indi...MrFixr55 — 05:51 PM
HiFi (Chifi) tube amp build - but my own design.
What may be lacking in the PP Tube amps may be the 2nd harmonics, which some, especially RCA back in the day called &quo...MrFixr55 — 05:32 PM
Jackson 715 not working
Usually in an emission tester, the tube under test is measured as if it were a diode. So, some testers connect all the g...RodB — 04:17 PM
Restoring Philco 37-604C
Yep. F5 is green, D5 is Red. Red is Bad. Green is Clean.morzh — 01:30 PM
Jackson 715 not working
I did start to do that but I stalled out because I could not figure out how the grid and plate get voltage. In this diag...daveone23 — 11:52 AM
Restoring Philco 37-604C
(Insert Homer Simpson "DOPF" Here.) When all fails, look at the can. Took the Ron Ramirez advice, red Caig D...MrFixr55 — 09:23 AM
Philco 91 Speaker Replacement
From your text I am not sure if you intend to use the existing speaker with a resistor instead of the field coil. It wo...morzh — 08:44 AM
Philco 91 Speaker Replacement
My field coil is bad. I am still hoping to find an original, but if I can't I will go with a fitting Philco speaker, 125...dconant — 08:34 AM
Philco 91 Speaker Replacement
As Rod said, it is OK to use a fitting speaker, and then look for an original one. If you buy a Hammond 125 output tr...morzh — 08:15 AM
Philco 91 Speaker Replacement
Yes, I often have to substitute, then keep an eye out for an original. In the meantime, the radio is working and being e...RodB — 08:02 AM

[-]
Who's Online
There are currently no members online.

>