SB-400 Low Power output problem.

[Mark Johnson/Ontario/IBM]

Just want to thank everyone that replied to my posting re: SB-400 low
output. In the end I've come with output power as follows: 80M - 100w, 40M
- 100w, 20M - 95w, 15M - 95w, 10a - 45w, 10b - 55w, 10c - 50w, 10d - 30w.

Heres what I did/found:

My main problem was the watt meter I was using was very stingy. It was part
of a KW Super Tuner match box with internal dummy load. When I hooked in a
Heath HM-2140, I got much higher readings on the 15 and 10 meter bands.
The HM-2140 could also be off, but it seemed to respond better during
testing.

I found that adjusting the grid driver coil  had the same consistent peak
right across the 10M bands. It was the PLATE  coil that was band sensitive.
In the end I peaked in on the 10b band and then got fairly even output
across the bands. 10d was/is a bit low but I'll be damned if I can
determine why..Design spec????

To recap, I replaced the finals with new 6146B's (They neutralized
perfectly by the way) which were Westinghouse English made, replaced the
6CLR driver, replaced V4 and V5 (Het Osc and Mixer) and checked all
voltages (all were right on).
I aligned that damn thing about 200 times..actually about 6 times. Twice by
the book.... only to find you've got to do Max Out peaking afterwards
anyway.

During all this I smoked out R25. The 6AV11 LSB, USB Carrier Gen tube
actually developed a short internally and took out R25. A nice little
diversion to take my mind off power output problems.

So, that's it..I think I'm at the end...If anyone has any feedback or
further suggestions on how to  get more power out than I can..I'd love to
hear from you as usual.

My thanks again to all that responded and to K6UUZ for reminding my to Read
The Frigging Book and do the alignment as indicated (Got to remove the Hi
voltage from the feedthru and the lead connecting the lead connecting pin 3
of V10 and V11).


Mark V. Johnson
VE3DJU

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