[Collins] 6293 in a KWM-2A?

[Gerald]

On Tue, 2005-08-23 at 10:25 -0400, Bill Abate wrote:
> I recently picked up an NOS pair of 6293's.  These are the pulse rated 
> 6146's.  According to the data sheet the grid to plate, grid to cathode 
> and all other inter-electrode capacitance values are identical to the 
> 6146's.  On the surface it looks like a direct substitute without any 
> problems.
> 
> Has anyone tried these tubes in a 2A?  Mine is a late RE with the air 
> variable for neutralization.
> 
> Thanks and 73,
> 
> Bill, K3PGB
> 
If they neutralize, the curves are the same for 6293 as 6146. Supposedly
the vacuum is higher, for sure the peak positive plate voltage rating is
higher for the 6293. Back in the late 50s and early 60s, 6293 were
popular for supposedly longer life in plate modulated AM rigs. I've not
ever gone that route, but unless the shielding under the plate cap is
short (like the 6BG6G version of the 807) to give more RF feedback there
shouldn't be any problem. And neutralization should take care of less
shielding. And I've run a 6BG6G at 6m with usable efficiency without it
oscillating despite the lack of internal shielding.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer