Wonks wrote:Difficult to say about stoppers, as fitting them is one of the standard list of recommended Princeton upgrades. So the Morgan PR12 circuit may well have them in, or it may not. But it does look like it's something to do with the return part of the reverb circuit as we know the radio interference level isn't affected by the input volume, just the reverb level control.
Slightly OT Wonks and I shall look for those mods soon but the stoppers point interests me.
One reason the concertina PI is not popular is that it is said to not sound good under overdrive? Merlin Blencowe is a great advocate of stoppers and says they fix that problem. I note the OP valve grids have only 1k5, low for even standard designs, 10k is more common but MB suggests 100k or higher. This will not, as many people thnk cause 'tone suck' and rob HF from the OP valves because being pentodes they have diddly grid capacitance.
In any event, 3dB down at 10kHz is easily good enough for gitamps.
Oh to be 60 again with the time and energy to play with this stuff!