[ARC5] OT - the BC-221-D, tube types.

[Leslie Smith]

Hello All:

I'm looking at the circuit diagram for the BC-221-D heterodyne frequency
meter.
 I see the tube used in the oscillator circuit has the part designation
 VT-77.
In the drawing I see a device with four grids - I haven't unplugged the
VT-77, but I suspect it uses the six pin UX-6 socket.

In the cross-reference list I see a VT-77 is equal to a type 77 pentode.
In the RCA datasheet I see tube type 77 is  described as a "triple grid
pentode".
In my understanding - this is a standard early pentode - and I would
guess not too much different from the more-modern (octal) 6K7 or 6SK7.

I believe the US military documents are often reliable; I cannot
understand why the VT-77 is drawn with 4 grids.

Help!!


73 de Les Smith
   vk2bcu at operamail.com


References:  (1) Technical manual for the BC-221-x series:  TM-11-300.
Circuit diagram for the BC-211-D is presented on pg 42 of that manual.
The tube data for type VT-77 or 77 pentode is available from Frank
Phillips tube data pages:
     Link to:    http://www.tubedata.org/   
               or     http://www.duncanamps.com/


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