WHAT AM I DOING WRONG?

[Stu Lyon]

Jeff,
I would check the carrier null pot (R109) and R401, which is the source of
the unbalancing current of the modulator. The 200 ohm nulling pot is famous
for suddenly opening up. I have replaced about six of them in various
SB-rigs with a 10-turn trim pot. The wire leads of the pot have to be spread
a little, otherwise it fits nicely on TOP of the board. If you do this,
replace the 220 ohm end resistors as well.

The story on R401 is that it drifts high and doesn't allow full unbalance of
the modulator in the tune/cw mode. I would replace it with something like
33K or 39K.

Good luck, working the SB-301/401 is a very nice combination.
see:  http://www.pacificnet.net/~plyon/images/w6cux-2.jpg

73, Stu W6CUX
Winnetka, CA
slyon at pacificnet.net



----- Original Message -----
From: "ejforwood Jerold Forwood" <ejforwood at MSN.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Tuesday, February 19, 2002 12:00 AM
Subject: WHAT AM I DOING WRONG?


Hi all,

I need help!

I have 2 SB-401's and I seem to have the same problem with both
transmitters.
The first one was working but had low output, only about 40 watts.  So I
started by cleaning all the relay contacts and band switches. Then I bought
a complete set of new/old stock tubes and started to realign the whole thing
according to the alignment procedure in the manual using my SB-301 connected
as a transceiver setup.  I could not get more than .2 Volts RF at pin 2 of
the 6CL6 driver as I adjusted the grid coils.  This was also the same case
as I proceeded on to the wire between the pins 5 on the 6146A finals and the
plate coils.  I have the 50ma bias, but I now have no output at all.  I have
good high voltage, but no grid or plate current.

I bought the second  transmitter an it is a good one.  The LMO dial works,
even the hairline.  It had about 50 - 60 watts out.  So I cleaned and
re-tubed and started with the realigning.  This time I used the xtal pack as
a stand alone.  I have good DC voltage at the oscillator test point but low
RF voltage from there on.   Now I have the same result, NO OUTPUT!

HELP!!!

Thanks and 73's,

Jerry, K0EJF

E. Jerold (Jerry) FORWOOD

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