what's the purpose?

[harris51]

of the 1meg resistor in the input jack itself? in a liver pool:?:

[rock_mumbles]

The 1M resistor sets the input impedance.

[paulster]

More importantly, if gives the grid on the first gain stage a reference to ground. Without that it'd be noisy as hell until that particular triode expired.

[Mark]

The input resistor has to be there to bias the valve. The grid would float to a higher voltage and destroy itself.

[brewdude]

The resistor does not have to be physically located on the jack. It is simply a convenient and effective spot for it.