need advice on jtm mod to bassman

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mixohoytian

mixohoytian

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So I got a 70s silverface bassman 100 a couple weeks ago or so
Having my tech friend mod it.
He recapped, got it working well, took out master volume, blackface to the normal and jtm to the bass channel
clean sounds fantastic


what I've found is that the jtm side sounds pretty cool at 4 on the volume
at 5 + it starts getting pretty gainy and undefined by 9 or 10
I understand that a JTM-100 watt doesn't exactly exist...
Is this unavoidable? I would prefer it to break up later
Should I just deal with it and realize that this mod is supposed to sound good around 40 watts-50 watts?
should I remove 2 tubes and make it a 50 watt instead?
 
is your tech friend not versed in altering the gain, partial gain or EQ response a stage?
 
he can alter the gain and deviate from the JTM spec
haven't tried it yet
12au doesn't sound good
12ax sounds better for what I want

amp sounds like a killer JMP now, not really a JTM
and I have it at 4 or 5 on volume

we tried pulling 2 tubes and he put in a 1/2 power switch
same thing, still all the tone u want at 4 or 5 and then nasty after that
I'm gonna just run it at 4 or 5
its way loud...

just bugs me that it's not useful any higher
 
mixohoytian":1xefelif said:
So I got a 70s silverface bassman 100 a couple weeks ago or so
Having my tech friend mod it.
He recapped, got it working well, took out master volume, blackface to the normal and jtm to the bass channel
clean sounds fantastic


what I've found is that the jtm side sounds pretty cool at 4 on the volume
at 5 + it starts getting pretty gainy and undefined by 9 or 10
I understand that a JTM-100 watt doesn't exactly exist...
Is this unavoidable? I would prefer it to break up later
Should I just deal with it and realize that this mod is supposed to sound good around 40 watts-50 watts?
should I remove 2 tubes and make it a 50 watt instead?
Click to expand...

Hi , the jtm100 does exist ,here is one.....
check the link
https://www.youtube.com/watch?v=OFlyLwbq8AQ
 
cool, yeah I've seen the jtm 45/100
from what I understand, they don't have the same airy chime that the 45 had..?
I don't think I'll be able to cop that...it does sound like this amp in the youtube, more agressive, more like the 1st 100 watt amp, acd/cd vibe



tone modder, I will try having him decrease the gain so I can get the most out of the power tubes
 
mixohoytian":2k7a6r5y said:
cool, yeah I've seen the jtm 45/100
from what I understand, they don't have the same airy chime that the 45 had..?
I don't think I'll be able to cop that...it does sound like this amp in the youtube, more agressive, more like the 1st 100 watt amp, acd/cd vibe



tone modder, I will try having him decrease the gain so I can get the most out of the power tubes
Click to expand...

the amp in the clip is serial number 7233 one of the first ever 100 watters to use el34

it doesent even have the steel chassis its an aluminium blockend chassis , its being pushed with a pedal in the clip , without a pedal the amp doesent breakup until around 7-8 on the volume ,then its a very low gain creamy overdrive ,its actually not quite as loud as most other hundred watters , this is partly due to the fact it only has 27k nfb attached to the 16 ohm tap and no bright caps in it

the low nfb acts like a clamp on the power stage so you can crank the amp without it busting your head open and it seems to reduce overall gain
 
thanks druckpig
I'll see if he can get it to break up later at 7-8
:thumbsup:
 
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