[MRCA] Frustrating BC-639 problem Solved

[Robert Flory]

Hello,

I've been beating my head against a newly-acquired BC-639 VHF receiver.  Despite all DC parameters looking ok like the grid bias resistor testing ok, plate resistor ok, the local oscillator would not oscillate.  The tuned circuit checked out with grid-dip meter.  No plate current.

I don't know what made me check, but in the process of figuring out what pin to inject some LO from an external source, I decided to take a look at the tube.  Despite the diagram in the manual and the one in my 1949 ARRL handbook showing both pins 2 and 7 of the 9002 being connected to the cathode, the Raytheon tube I am using has pin 2 connected to the getter.  The receiver uses pin 2 only to connect to the cathode.  No wonder I was getting nothing.

I ran a fine wire from pin 2 to pin 7, wrapped around the tube pins, put it back in and now the LO works.

Go figure

RF