Mk4 VTA board.....270k or 220k to bias?

On my Mk 4 VTA instructions I have a diagram and showing 220k ohm to the bias, but in the instructions/ schematic it says 270K? The parts kit I got had 4 220k and I'm sure that's what's supposed to go in there, but curious, why the switch?

Gord

Hi Gord,
I started switching to 220K resistors in that position about a month ago. It's not a critical value, and with some of the crappy tubes on the modern market, it reduces the chance of bias floating away from the correct setting, think of them like pull-down resistors in a semi-conductor circuit, the lower value gives a little more stability.
Amps using KT88s rather than EL34 usually use 180K or even 150K.
I'll update the parts list, but I probably marked your parts list when I checked it off showing the change to 220K, even though it's not that way on the schematic.
Roy www.tubes4hifi.com