High Plate Stages--Which Combinations Work for Which Amp?

[David Root]

So we have 220K/3K3, 180K/2K7, 150K/2K2 and 120K/1K8. Which pairs best suit the different D-amps, in which part of the circuit, and why?

Also, has anyone tried 270K/4K1 or 330K/5K anywhere? Pretty low current I think.

[exocet]

I'm not aware of any common valve amp designs (for guitar at least) that go above 220K on the plates. As you increase the plate load resistance you get lower 2nd (even) harmonic distortion but increased odd harmonic distortion. In practice this can give rise to a very 'shrill' sound. It will also lead to a more sudden transition from unclippped to clipped signal. Overall it's not likely to produce a pleasant overdrive but there again tastes will vary.

[David Root]

I think some 4-stage metal preamps go above 220K on the third stage.

[ayan]

I think some 4-stage metal preamps go above 220K on the third stage.

The Mesa Boogie Mark IIA/B had a stage with a 330K plate load resistor, and the IIC+/III/IV had an overdive stage with as high as 270K. They were not metal amps to me, and to varying degrees, I think they were all known to be "smooth sounding" amps in the grand scheme of things. I believe that the higher the plate load resistor, the more abrupt the transition to "harder" overdrive seems to be. After almost a decade of experimentation, I eventually settled for 100K plate load amps for that reason.

Cheers,

Gil

[David Root]

Thanx Ayan, for the benefit of your experience. I'm building my first high plate now, a BM/HRM, so I'll be able to see for myself soon. My first two were 100K plates thruout.

I wasn't thinking of Boogies as metal amps, but much newer stuff.

[ChrisM]

The older Boogies were really cool amps, in design and sound. Always liked them.

Curious to here your findings on high plate values David.