6146 Replacement

[Kenneth G. Gordon]

On 26 Aug 2006 at 12:47, Glen Zook wrote:

> Many of the transmitters that were designed for the
> earlier versions of the 6146 are definitely NOT
> "happy" with the 6146B.  Often the 6146B / 8298A will
> not neutralize in transmitters designed for the
> earlier versions.
>
> <snip>
>
> with the 6146B / 8298A and I believe them.  But, in
> the vast majority of cases replacing the earlier
> versions with the 6146B / 8298A causes problems.

I am certain you are right in your analysis of this problem, and I follow 
your recommendations as closely as I can with my more sophisticated 
rigs.

However, in the case of the DX-40, or, for that matter, the DX-35, I think 
there is much less of a chance for problems using the 6146B in these 
rigs.

For one thing, they aren't really neutralized in the traditional sense: if I 
remember this correctly, the grid circuit is so designed that the PA 
stage is unconditionally stable no matter what tube you use there.

Again, if I remember correctly, the grid circuit is a LOW IMPEDANCE 
design, and cannot contribute to oscillation in the PA.

In my callow youth days, I substituted several different tubes and/or 
sockets for the final amp in my DX-35, including a 4X150A, and had no 
problems with instability in the PA with any of my odd-ball substitutions.

I really think that in the case of the DX-35 and DX-40, one can safely 
substitute any 6146 variant with no problems.

I intend to verify this in my DX-35 at the first opportunity.

Ken W7EKB

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