Richard,
I performed an electrical restoration on an SP-600 (JX-26)
last summer. The frequency accuracy was poor....WWV at
10 MHz was at 10.2 MHz (approx). What is worse IMO is the
tracking across the bands. The frequency at one end would be high,
but at the other extreme, it'd be low.

I'm sure this can be tuned out. I just haven't tried yet.

I'm in the process of bring back another JX-26 now, so if
you have any specific questions, you can write me off list.

Steve W6SSP