Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12, 2025) x

Thread Closed

Philco 81 Front End Problem
#6

I pulled the chassis. Nothing seems to be way off. The antenna coil primary measures 3.2 ohms to ground. That could be a little high. The secondary measures 6.6 ohms total. One section measures 2.3 ohms and the other 4.7 ohms. Resistor 10 is new and measures 6k. Capacitor 5 is new and is 1500 pf, 630wvdc +/- 20%. It is a film capacitor. Maybe I can find the old mica capacitor. The oscillator coil section that is in the cathode circuit of the 1st detector measures 3.9 ohms to ground, which is normal. All of the tuning capacitors and trimmers show open circuit at DC. The oscillator coil 12 measures ok. The voltages on the 1st detector tube are: 275 v on the plate, 99.4 v on the screen grid, 5.04 on the cathode, and 0v on the plate. This was when the tube was not oscillating. I don't think anything changed when the oscillation started.

The police band switch doesn't seem to be interfering with the ciruit.

The symptoms are the same, the oscillator won't start until I remove the 1st detector grid cap and it keeps oscillating when the cap is replaced onto the tube.


Messages In This Thread
Philco 81 Front End Problem - by Guest - 02-02-2009, 07:56 PM
Re: Philco 81 Front End Problem - by exray - 02-02-2009, 08:41 PM
Re: Philco 81 Front End Problem - by Guest - 02-02-2009, 10:00 PM
Re: Philco 81 Front End Problem - by exray - 02-02-2009, 10:45 PM
Re: Philco 81 Front End Problem - by Steve Davis - 02-02-2009, 11:12 PM
Re: Philco 81 Front End Problem - by Guest - 02-05-2009, 08:48 PM
Re: Philco 81 Front End Problem - by Guest - 02-06-2009, 06:45 PM
Re: Philco 81 Front End Problem - by exray - 02-06-2009, 07:01 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
54C Complete Teardown/Rebuild
Hello Roy, here is this one sincerely Richardradiorich — 12:45 AM
54C Complete Teardown/Rebuild
Richard, Had grabbed it already but thank you just the same.  I find myself wanting to find some way to block out the...glyphmon — 12:03 AM
54C Complete Teardown/Rebuild
Hello roy, here is a link to the schematic . Sincerely Richardradiorich — 11:54 PM
54C Complete Teardown/Rebuild
Richard, The Silvertone 2014 also is a transformerless set, so I am incorporating a 1:1 600 ohm audio isolation transfo...glyphmon — 11:37 PM
Preliminary work on wife's Silvertone 2014
Did an alignment today which was interesting.  IF alignment went great, almost all was already spot-on.  Adjusting on th...glyphmon — 11:35 PM
54C Complete Teardown/Rebuild
The main problem with adding a Bluetooth input is that this set lacks a traditional power transformer to isolate it from...radiorich — 11:19 PM
54C Cabinet Refinish
I started stripping this cabinet before it got super chilly out because I knew I wasn't going to be able to work on ...glyphmon — 11:18 PM
54C Complete Teardown/Rebuild
While I'm waiting to wrap up the final steps on my wife's Silvertone 2014, I started disassembly on the next project.  O...glyphmon — 11:07 PM
Preliminary work on wife's Silvertone 2014
Hello roy, that great news glad it worked out for you !! Sincerely Richardradiorich — 10:50 PM
Preliminary work on wife's Silvertone 2014
Safety caps arrived today.  Soldered one in and had a successful first power-up.  No magic smoke escaped and it tunes in...glyphmon — 09:53 PM

[-]
Who's Online
There are currently 2268 online users. [Complete List]
» 1 Member(s) | 2267 Guest(s)
Avatar

>