1. The PHILCO Phorum
  2. Philco Radio Discussions
  3. Philco Electronic Restoration
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Linear Mode
A 38-15 fading triubleshooting
Mondial
Phorum Expert
*****
Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
#2

07-19-2014, 09:34 PM
Seems like the 78 is gassy or has grid emission. When the voltage rises it may reach the point where the gas ionizes and causes the control grid to go positive.

Tubes can develop some weird problems. I had a 39/44 tube that did something similar. Radio would play fine for a few minutes then gradually reduce volume. Found AVC line went from normal negative condition when receiving signal to slightly positive as it warmed up. Replacing the tube cured the problem.
Find
« Next Oldest | Next Newest »


Messages In This Thread
A 38-15 fading triubleshooting - by morzh - 07-19-2014, 08:00 PM
RE: A 38-15 fading triubleshooting - by Mondial - 07-19-2014, 09:34 PM
RE: A 38-15 fading triubleshooting - by morzh - 07-19-2014, 10:02 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
HiFi (Chifi) tube amp build - but my own design.
Tim, nice write up and thanks for sharing !! Sincerely Richardradiorich — 02:47 AM
HiFi (Chifi) tube amp build - but my own design.
Well, this was a real "Hum-Dinger" :lol: ! This will be kinda long, but hopefully it will help others having t...TV MAN — 01:55 AM
Shadow Meter Bulb
Phorum members, I am trying to find the bulb # for PHILCO Shadow Meter part number 45-2180 that is from a 37-640 chassis...georgetownjohn — 06:53 PM
Philco 41-608 changer coupler
3D-printing...short of machining, of course. Or molding.morzh — 05:20 PM
Philco 41-608 changer coupler
Thanks, Morzh. That solves the issue of the rubber pieces. Now, I need to find a way to replicate the pot metal piec...alangard — 05:07 PM
12' Philco
If it is 12', either Kareem or Andre would have to jump pretty high to look at the front panel. Kareem would have an e...morzh — 01:48 PM
12' Philco
And here's a story about the tires on the truck. Same "no-stoop" guy must have installed these! Take care a...GarySP — 01:17 PM
Hickok AC51 tube tester
I think they have only shown the secondaries of the transformer. Two of them feed the rectifiers' filaments.morzh — 12:58 PM
IF can wire size and Rubber mounts?
Arran If the wire inside cans is the gauges you mentioned, the sole reason for that would be mechanical, to stiffen t...morzh — 12:56 PM
12' Philco
Rod, Yes, I know, but the Giant Philco is not around anymore either, so I go by whoever was alive fairly recently. H...morzh — 12:54 PM

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

>
  1. The PHILCO Phorum
  2. Philco Radio Discussions
  3. Philco Electronic Restoration