I had a 1.5" diameter Philmore vernier dial
laying around so I decided to see how difficult it would be to install for
tuning the Bayou Jumper which is sort of fast and difficult, but not
impossible, to get just right.
First, it was necessary to drill out the hole in the
panel for the tuning pot to a diameter of 7/16" to allow for clearance of
the shaft coupler on the vernier. Next, it was necessary to cut the
tuning pot shaft down to just over 1/4" long and the bottom of the shaft
coupler still bottomed out on the frame of the pot, leaving the base of the vernier
mechanism about 1/8" above the panel. There are two options here,
grind down the shaft coupler until the vernier sits flush with the panel and
the coupler doesn't bind on the frame of the pot or use 1/8" or so of
spacers between the panel mounting standoffs and the panel (easier at assembly
time to add the spacers between the main PC board and the bottom of the
standoffs). The mounting holes for the vernier must be carefully laid out
and drilled for 2-56 screws and 2 of these are used to mount it to the panel.
Before re-assembling the panel/pc board combination,
set the shaft on the tuning pot to mid range and the vernier to midrange
(#50). Carefully fit everything into place, tighten all the
panel mounting screws and other top side hardware just like you did on the
initial assembly. Next, very carefully tighten the set screw on the
vernier's shaft coupler to lock it to the tuning shaft of the pot.
You will only have 180 degrees of rotation rather than the full 270 degrees but
this should fall within the 7020 to 7130 range assuming you had done the
calibration steps earlier.
I used the 1.5" Philmore S38 vernier. The
S50 is a 2" diameter dial and these are also available for somewhere
around the same price or just a little more. The S38 is the ideal one as
it fits within all original markings on the Bayou Jumper's panel where the S50
will cover the word Tuning and the top will extend into, if not completely
cover the original V shaped pointer at top center.
It's a daunting modification and probably most won't
do it, but it does really slow down the tuning and makes it much easier to tune
in a CW station and it's now actually possible to also tune in the SSB stations
at the high end if they fall within the tuning range. The radio is quite
stable and once tuned to a frequency I didn't observe any drift after a couple
minutes of warm up. Super job by the designers.
It actually looks pretty decent mounted on the radio -
helps a lot with ease of tuning in a signal.
Closer picture of the installed Philmore S38 vernier