TS-820,a little off topic

[Glen Zook]

Replace the 6146B tubes with either 6146 or 6146A
types.  The 6146B IS NOT the same tube as the 6146 /
6146A.  Sometimes they work when used to replace the
6146 / 6146A tubes, but quite often they do not.
Heath did NOT originally use 6146B tubes although I
understand that they, along with Collins Radio, when
RCA first came out with the 6146B in 1964, said that
it was OK to replace the 6146 / 6146A with the 6146B
tubes.  But, after a very short time, problems
developed and that "OK" was rescinded.

What is happening is that the 6146B tubes are "taking
off", that is oscillating at VHF frequencies.  That
results in overheating of the tube since they are
pulling excessive current.  The cathode resistors are
"burning out" due to the fact that excessive current
is being pulled through them.

A quick way of telling if the 6146B tube will work is
to neutralize them.  If they will not neutralize, then
immediately replace the tubes with 6146 / 6146A types.
 If they do neutralize, then watch them for several
days.  If the neutralization does not hold, then
replace the tubes with 6146 / 6146A types.

The question of 6146B tubes comes up at least 5 or 6
times a year on every reflector that I subscribe to.
Because of that, I wrote an article for Electric Radio
that was published in the February 2002 issue about
the 6146 family of tubes.

If you desire a copy of the article, I can E-Mail it
in Word 2000 format.

Glen, K9STH


--- oh8jep <oh8jep at KOTINET.COM> wrote:

Final tubes are 6146B,the same type as Heath use,and
I have changed them to new ones (German made 6146B)
because those cathode resistor always burned  ( 10
ohms/1W),but it did not help,the same problem
continue. All seems to be OK,I can tune up the finals
normally, the power output is normal 90-100W but after
a one 15minutes period of SSB QSO,it is almost sure
that those resistors burns.


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