SB200/201 Comments & Questions

[Tom Ruhlmann]

I have completed rebuilding of an SB201 - about the only things original now
are the transformer, chassis and RF decks.  New Harbach antenna relay, power
supply, soft start, soft switch modifications and new tubes along with almost
all new wiring, resistors and a meter conversion from an HM102.  Seems to
work well with 500 to 600 watts out on 75, 40, 20 and 15.

Driving with an FT1000MP.

I have noted the following:
    There is very little grid current at full output.  Approximately 5 ma. or
so.

    Plate current idles at about 80 to 100 ma.

    Can load plate to 450 to 500 ma. at approx. 2100 volts.

    I noticed the plates glow when at full output on 20 during extended rag
chew.

    I "tuned" the slugs in the tuned input circuits with about 10 watts input
(FT1000     tuner operational at the time).  There is only the slightest peak
- the Q seems very  low. I had expected a much sharper peak - it is hardly
noticeable.

    I did add a pilot light and an LED + resistor across the antenna relay
coil to     indicate transmit mode.  I know that it lost collector value when
I drilled the panel     but I wanted the indicators.

    I still need the cover for the PS / RF cage area.  That was not included
in the  "really great deal" that turned out to be a good learning experience.
 The original   meter was also missing.

    Any comments about the SB200/201 operation, performance, parts etc. would
be greatly appreciated as this is the first linear I have dealt with.  Forty
years a ham and still barefoot.

    Looking forward to hearing from those who have some experiences with the
200/201.

Tom Ruhlmann,  W9IPR

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