6146 Replacement

[Glen Zook]

Actually, Class "C" is usually even worse than Class
AB-1 for problems with the 6146B/8298A.  However, in
the DX-35 and the DX-40 (also, to some extent the
DX-60) the grid circuit is very heavily loaded to keep
the final amplifier from having to be neutralized. 
This was pointed out in the QST article when the DX-35
was first introduced.  But, using the 6146B/8298A in
the DX-35, DX-40, or DX-60 is a "crap shoot".  

The 6146B/8298A is less likely to "take off" in those
transmitters because the grid is heavily loaded.  But,
it can still happen and you have to be VERY careful if
you substitute the later tube for the earlier
versions.

Heath recommended the 6146 and the 6146A/8298 over the
6146B/8298A.  They did furnish specially "culled"
6146B/8298A tubes late in the production of the
HW-101.  This was because their supplier was not
furnishing the earlier version for a while.  Those
specific tubes were probably those that did not meet
the maximum gain characteristics for the 6146B/8298A
but would work fine when substituted for the earlier
versions.

I have heard from a number of people who have never
had any problems with substituting the tubes. 
Frankly, I definitely believe them.  But, in the vast
majority of cases using the later version in place of
the earlier versions causes problems.

What is happening with Ken's HW-101 is that the final
amplifier is putting out spurious signals which is the
problem that happens most when the 6146B/8298A is
substituted for the earlier versions.

Glen, K9STH



--- "Kenneth G. Gordon" <kgordon2006 at VERIZON.NET>
wrote:

However, on the back of my recently restored HW-101,
there is a sticker which obviously came with the kit
that says something very close to, "Use 6146A type
tubes ONLY in this transmitter"

However, I recently discovered that when I tune the
rig up on 40 meters, the GFCI associated with our
basement refrigerator ALWAYS trips.









Glen, K9STH

Website:  http://k9sth.com

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