--- In
ModularSynthPanels@yahoogroups.com, James Elliott
<johans121@...> wrote:
>
> Now, it very well may be possible to use a SPDT switch to do this,
> however upon a novice's first (or second, third, fourth) glance it
> seems that the jumper switches between to pins on the tube - so I
> don't know that a SPDT will work without some other circuit voodoo
> magic. I'm writing this at work so I can't necessarily verify what
> I've just said at this moment....
Since I'm building one this evening, thought I'd follow up.
There is a bit of voodoo. It looks like Ken intends for
pin 4 of the tube to be at the same voltage as the 330K
bias resistor so the 'outside' of both options are actually
connected on the board. (You should be able to follow this
on the PCB with little effort.) The voodoo then is to send
the three pads involved in the jumper option (i.e. not the
330k resistor option) to the SPDT switch. Then solder the
330K resistor from either of the two left pads (they're
connected) to the center pad of the jumper set. (It will
actually work better if the resistor is put in first in
vertical position giving you a solder point for the middle
wire of the SPDT run.) The voodoo makes it a bit harder
to try tweaks but that's the tradeoff...