Matchless HotBox - different pot for gain...

[Guitartoma]

I have a Sampson era Matchless HotBox which sounds amazing. The only problem I have is that there is very little control over the gain. It's all or nothing with this thing. From 0-1 there's little to nothing, medium to heavy gain at about 2, then it's all 'over the top' gain from there to 10.

The pot that controls the gain is a 1M 2watt reverse taper. It's a big sucker! Would changing that to a linear pot make a difference?

Does anyone have experience with a HotBox?

Thanks for looking!
-Tom

[terminalgs]

the linear pot would ramp up slower than the reverse audio pot and it'd probably move the 0%-20% gain variation to 0%-50%.

I built a pedal very similar to the hotbox.    the waveform shape and amplitude at the plate of V3 is almost exactly the same when
the gain is anywhere between 25% and 100%.       the gain control varies the amplitude going into V2.    gain is fixed between V2
and V3 with a 470K/470K resistor voltage divider. 

When I built mine,  I scoped it out with a input signal that was 700hz or so 0.5v point to point (P2P) sine wave.     The signal on V3's grid was a clipped, 'squared off, 25v P2P with the bias well below zero (top of the waveform heavily clipped, the bottom was not clipped).    The signal looked nearly identical to this  all the way down from 100% to about 25% gain control.   I had 6v p2p on the grid of V2 @ 25%  and about 20v p2p @ 100%...  so give V2 anything more than 6v and the clipped waveform leaving the final gain stages isnt much unchanged beyond that.

Audible tests were the same--  not much difference in distortion from 25% to 100%..  This is pretty much as you describe it sounding.

you might be in luck to try an easy no-solder swap if V1 is pins 1,2,3 of a 12ax7.  If it is, you could swap the 12ax7 for a 12dw7 (twin triode
with a low mu triode of 1,2,3 and a high mu triode on 6,7,8).  the low mu section of a 12dw7 has a mu of 20,  the high mu section has a mu of 100. so its 1/2 a 12au7 and 1/2 a 12ax7.     so instead of a 25v p2p produced from a 0.5v signal,    it'll be about ... 6v  (although a 12ax7 has a mu of 100, the way V1 is biased in the hotbox,  its more like 60.  so.. to guess: (60 real mu / advertised mu 100 ) = ( 12 real mu / advertised mu 20 ) my test 0.5v waveform   would be more or less 6v instead of more or less 30v.

of course,   my 700hz 0.5v p2p is  not the same as a guitar signal.  but it shows that the 12dw7 swap might be worth a try...