Long Plate vs. Short Pate preamp Mullard?

[Brandon]

Can anyone tell me the difference in tone the short plate and the long plate mullards have?

My other question is what is the likelihood of a long plate or short plate mallard showing up in a stock '68/'69 Marshall 100w? Did the short plates show up more or vice versa? Or perhaps one didn't show up at all?

[demonufo]

Long plates weren't made by the time Marshall came around, and hadn't for some time. I wouldn't ever expect to see one as stock in a Marshall.

[Mr Crumb]

You'd likely find an I63 Mullard in a late-60's marshall. Long plates(mC1, f91, f92) were gone by the very early 60's. Long plates sound nice, but are excessively microphonic.