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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, 06:56 PM
Re: Philco 81 Front End Problem - by exray - 02-02-2009, 07:41 PM
Re: Philco 81 Front End Problem - by Guest - 02-02-2009, 09:00 PM
Re: Philco 81 Front End Problem - by exray - 02-02-2009, 09:45 PM
Re: Philco 81 Front End Problem - by Steve Davis - 02-02-2009, 10:12 PM
Re: Philco 81 Front End Problem - by Guest - 02-05-2009, 07:48 PM
Re: Philco 81 Front End Problem - by Guest - 02-06-2009, 05:45 PM
Re: Philco 81 Front End Problem - by exray - 02-06-2009, 06:01 PM



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