Peacekeeper with different JFETs

[MarkL]

I have a Peacekeeper PCB I've been waiting to build up, but find that at the moment I don't have quite enough J201's to use.  Is it possible to substitute some 2N5457's one one of the gain stages, perhaps the second to last (the "double" one)?  If so, would I have to adjust the 10M resistor on that stage?

[reddesert]

This is a theoretical answer since I have never built a Peacekeeper.

The third gain stage of the Peacekeeper is a single JFET, common-source amplifier. This is a very typical JFET stage (lots of Runoffgroove circuits use it), but it has to be biased into the correct range of Vdrain to work right - why there is a trimpot on the JFET drain. This biasing depends on the JFET properties and the gain depends on the drain resistor. So let's not substitute that one.

The first two stages of the Peacekeeper, each with two JFETs stacked, are variations of the mu-amp or Jack Orman AMZ "mini-booster." Some information and history:
http://www.muzique.com/amz/mini.htm
http://www.geofex.com/Article_Folders/foolwfets/foolwfets.htm
http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm
The Geofex articles by RGK go into some more detail about how the circuit works. Interestingly, although it's sort of a push-pull amp stage, RGK points out that the two JFETs are not doing symmetrical work. The lower JFET is responsible for the gain and the upper JFET is acting as a current source to help it pull the output voltage up.

My interpretation of this is that the sound / available gain will be dependent mostly on the properties of the lower JFET in each pair, so if you were going to substitute for something, I would start by trying the upper JFET in the mu-amp pairs. You shouldn't have to change the 10M resistor that biases the upper JFET's gate.