[Johnson] My Viking II

[Glen Zook]

What happens is that the 6146B is much more unstable
than the 6146 / 6146A / 8298 and they tend to "take
off" with all sorts of VHF parasitics.  The tube
literally "runs away with itself" and they often "burn
up" in a hurry.  If they don't "burn up", they often
are putting out all sorts of spurious emissions.  This
won't show up when using a dummy load since a dummy
load is "broad banded".  But, when transmitting into a
resonant antenna the SWR (or reflected power) is often
very high because a good part of the power being put
out in not on the frequency that you think it is!

The problems don't always happen right away, sometimes
taking several hours to appear.

It is unfortunate that RCA called the 6146B by that
name since it really is a different tube with the same
base connection.  At first RCA said that you could
directly substitute the 6146B for the earlier tubes
and all of the manufacturers went along with this. 
Unfortunately, it was soon apparent that the 6146B
caused all sorts of problems especially with
neutralization circuits.

However, there are individual transmitters and
transceivers within any line that was designed around
the 6146 / 6146A / 8298 that work fine with the 6146B.
 I have seen transmitters with almost consecutive
serial numbers in which one worked fine with the 6146B
and two others wouldn't work at all!  It is just
little things like exact wire placement, component
tolerances, etc., that add up favorably for the 6146B
in some cases.

The article goes into more detail about the
differences in the various members of the 6146 family.

Glen, K9STH


--- KENNETH A CRIPS <w7itc@msn.com> wrote:

I have read that excellent report on the 6146 tubes
this is why I finally installed the two 6146B's I have
as a last resort all of My 6146's where bad.  I am
curious what does the transmitter do if it doesn't
like the "B" version.

=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try it!
http://webhosting.yahoo.com/ps/sb/