Why Mesa use so many JFETS in the Road King?

ROOG

Looking at the schematics in an earlier post, I'm curious as to why Mesa show/install JFETS in the cathode circuits, the reverb and the FX loop circuits in the Road King?

I've not seen this done by others, is this common and what does it achieve?

Waiting on knowledgeable amp techie people with anticipation.

jpfamps

They will be used for the switching.

JFETs make very good switches.

ecc83

jpfamps said:

They will be used for the switching.

JFETs make very good switches.

Yay! FETs such as the J111, J112 are made for such signal switching duty. They are deployed in very high end mixers for signal routing and with the correct support circuitry are virtually "transparent".

Certainly gitamps and pedals will not use such super optimized circuits but the FETs contribution to signal degradation will still be minscule...Tis only rock and roll!

Better than relays in some ways, much lower cost and power drain and "coil thump" is very hard to eliminate in high gain circuits.

Dave.

ROOG

Oh yes, I've looked again and I see the remote gate signals from other sections of the schematic.

http://www.tonymckenzie.com/rk-2-schematic.pdf

Bit of a techie beast as tube amps go isn't it!