[R-390] Slowing main tuning for SSB

[Dave Maples]

All: With NOMEX inners and Kevlar outers, I bravely ask the following:

I have paired my 390A with a Johnson Valiant II with SSB adapter.  With 100
kHz per knob revolution, the main tuning for the 390A is a bit fast for SSB.
Using an external SSB adapter doesn't solve this issue unless one uses the 8
or 16 kHz filter and uses the external adapter to move around within the
filter passband.  That kinda defeats the purpose of the narrow filters in
the 390.

Has anyone ever added any sort of reduction gearing for the main tuning to
slow it for SSB?  I'm curious to see how other folks have handled this.

I am thinking about a metal bracket secured to the front of the 390A using
the three Phillips screws that are (a) above the LOCAL GAIN control, (b) to
the lower left of the LOCAL GAIN control, and (c) to the right of the RF
GAIN control.  This bracket would stick out from the front of the 390A far
enough to allow a Jackson Bros 6:1 or similar gear reduction device to be
used on the main tuning shaft.  The LOCAL GAIN and RF GAIN controls would
have to be extended (no big deal there, I don't think).

By doing this this way, the modification could be completely removed if I
choose to sell the rig.  It's a fair amount of metalwork, but I don't see
another way to add any sort of reduction in a way that can be easily
reversed.

Thoughts?  Brickbats?

Dave WB4FUR