[R-390] The case of the 6C4W tubes: last warning.

[Jacques Fortin]

The chapter 48 of the TM11-856A, page 36 mentions: 
Do not to substitute type 6C4W for a 6C4. 
The differences in characteristics are such that the type 6C4W will not
operate properly in the receiver.
The Y2K-R3a flagged this as a "severe error".
But maybe not...
When I got my 3rd R-390A, it came with Raytheon branded, "dwarf sized" 6C4W
in the 3 mixer positions and the receiver performance was very poor, until I
changed those for some "run-of-the-mill" 6C4 tubes.

 

I then remembered the warning that was written inside the TM11-856A. 

By careful inspection, the internal structure of these "dwarf" 6C4Ws was not
the same as any other 6C4 I had seen, but it nevertheless looked familiar.
They looked identical to the one of 9002 tubes, both in size and shape of
the internal structure, so I performed more tests.
Those 6C4W tested almost "on target" for the bogey value the published 6C4
characteristic.
Ep = 250V
Eg = -8.5V
Ip = 10.5mA
Gm = 2200 µS

But when their whole curves family was compared to the "standard" 6C4 one,
it did not match overall.
And when these tubes plots were compared with the published 9002 curves, the
match was almost perfect...

My conclusion is that those Raytheon branded 6C4W are really "recycled" 9002
tubes structure and this can explain why they are less performant as mixers
than the other "standard" 6C4s.
But I already hear your objections: basing of the 6C4 and 9002 differs only
by one pin: the cathode of the 9002 is connected to both pins 2 and 7 but
the 6C4 cathode is connected to pin 7 only.
Believe it or not, those Raytheon 6C4W have also their cathode connected to
pin 7 only, but the whole family of curves they plot is the published one
for the 9002 tube.

So -maybe- the TM11-856A warning was not an error, after all.
For the 6C4W other than the "dwarf" Raytheon branded ones, they can be
"legitimate" 6C4s if their internal structure is identical to some other
"standard" 6C4 tubes.


73, Jacques, VE2JFE in Montreal