[AMPS] Kenwood TS450 & SB-200??

Roger D. Johnson n1rj@ime.net
Fri, 14 Aug 1998 20:01:41 -0400


Hi Tom...

I know you addressed this to Rich but can't resist
putting in my two cents worth. When I
was planning to QSK my Drake L-7 amp for use with
my TS-940, I used a scope with
triggered sweep to take some measurements. These
times may not be exact as I don't
have the info right at hand and am going by
memory.

Key down.....scope triggers
5 milliseconds....940 starts producing output
6 milliseconds...940 at full output
15 milliseconds...L-7 relay starts to switch
20 milliseconds.. L-7 relay switched after some
contact bounce.

As you can see, the 940 was producing full output
BEFORE the amp relay had even started
to move! That is HOT switching!!!

Another interesting thing I found was that the
switching voltage to the TR relay in the 940 was
delayed 3ms from key down. It took another 2ms for
the TR relay to switch. So with the
stock radio, the TR relay barely made contact
before the 940 started producing output! To
help the situation, I found a voltage that went
high right at key down and used that to drive
a power FET to switch the amp relay. That gained
5ms but as you can see by the times
above, still not good enough for QSK. I replaced
the old 2 pole "clacker" relay in the L-7
with a vacuum relay on the output and a fast
acting 2 pole relay for switching the input and
bias. I was motivated to do this by Rich's fine
article on QSKing the TL-922. I did not
follow his scheme exactly but it worked out well.

73, Roger


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm