JTM 45/100 - Build story

[Xplorer]

Thanks guys.
Yes, no, i didn't try the 33 uf rifa yet, just been methodic and parient, waiting for a bunch of tests before starting to pull components, but i will.

I'll post a little sample of who knows some of these days, cause it had a distinctive signature , despite the problems here.
Looks promising anyway.

I allways have hard time with my login access on plexi palace, but why not, maybe some day.
I think too that neil is on a good track ^^ and i appreciate, really.

[neikeel]

Funny but I plugged my 45/100 in today - no pedals etc.

Yes it is very clean with my strat too('62 RI with C/S fat 50s pups so nothing special) - it is remarkably clean in fact all the way up to 8 on the dial when it does crunch. However plug in with Les Paul (BB3 bridge, Bare Knuckles Mule neck) and it is a different story. That odd modulation effect you hear with your recording maybe a preamp tube?

I use this amp for bigger venues but mainly for its clean funk/pop stuff and use my pedals and my guitar (Martyn Booth coil taps) to get crunch and more, so I don't usually worry about how clean it stays with just a guitar. I have an octave fuzz which is ok but having heard the Guitarist clips of the JD Hendrix Fuzz I want one of those, or to build a clone (anyone sell round clone cases for these?

As a comparison I put it back to back with my 67 50w Black Flag (ie well run in original) which has much more grind and importantly touch sensitivity with the strat.

I would still play your 45/100 much more, soak it over night a few times as well.

There are ways to get more grind too (use the low voltage PT taps, increase the 8k2 dropper to 18 or 20k, lower the screens voltage, or add some NOS carbon comp 100k plate resistors that measure 110k or even some earlier break up preamp tubes

[Xplorer]

Hi Neil !
Ha ha, even you are surprised ?
yes, with my jd blue fuzz, it's a different beast. but i'd tweak this fuzz first, because once switched on, it turns the thin-crystal trebly highs , alot, into some bassy stuff. it doesn't cut enough and i have to roll the fuzz knob close to zero.
i'll probably compare with my next home made fuzz coming, and put a 100k pot instead of the 500k vol pot. maybe change a cap too and tune the little trimmers. yes, the enclosure looks very cool , anyway you're right, get one of these, they're cheap.

about the oscilation ... maybe my iphone recording ? i'm not sure of what you're hearing.
the amp sounded quite different when louder, for sure, but it had some ac buzz, too much, not playable. ( maybe because of the room or ... the attenuator standing on the cab maybe ? )


i suppose thyat i should replace the two 5k6 resistors for three 1k5 or 5k6 ? to prevent from oscillating ? ( btw, i'm not sure to hear what it's supposed to do when oscillating, never experienced it )

when i played the guitar close to the amp, it didn't really feedback, it did wierd sounds, and only one tube went blue ( V4 i think ) with blue electric cloud when playing hard, you know ..

would you still be ok, just to be sure, to check with me the voltages on your turrets, and me on mine, on your amp and my amp, to compare ?
i'd do a list and post it.

then, i want to try with a rifa 33uf instead of the 16 uf.
i'll put another 250pf brown RS cap
the 100k plate resistors are those going to pin 1and 6 of V1 ?

i'll try with a lower voltage tap, like 220v, so 230v coming in it, and more output ?
but i thought it would be the opposite : 230 volts coming into 240v primary would give saturation ( VH way since he uses a 90v variac into the 120v input i think )

8k2 dropper to a higher value, ok ..
How to lower the screens voltage ?
i tried different preamp tubes, no much changes.
i might put some 470k instead of some 270k.

i'll give a try again with my telecaster which has a seymour humbucker antiquity in the neck, though the first strat i tried ha a kind of humbucker in the bridge ... it's the loaded pickguard of my old 91 jeff beck strat, lace sensors gold, loaded onto a strat made with different parts.

Yes, first, i'd like to get rid of the wierd sounds, or oscillation if this is what it is, and then fun will begin, work on the desired tone i want with it.

edit : right now i'm playing it with my telecaster. i think it has more output on the guitar.
Anyway, there's more saturation on this amp than in the beginning. strange thing.
the input of the amp seems very sensitive to the output of the guitar used.

[Xplorer]

This is how it can sound through one of the four outputs ( each is one 30 w speaker actualy ) of my attenuator at noon, feeding my spl transducer speaker simulator, direct out feeding the sound card, feeding the IR speaker sim, feeding altiverb in cubase.
1969 Telecaster played, texas special in the bridge, antiquity humbucker in the neck.
bright volume on ten, p^resence crancked. basse to 0.

This is wierd, the problem seems to solve by itself ^^
the cab sounds quite close to it too.

i'll check with a strat now.

[VintageCharlie]

Seems like gainwise its where it should be. Still it seems to beatad on the thin side (though that can be expexted with the settings you mentioned. Some of the fizz will probably go away too with time. Wy amp got smoother and any trail of initial fizzies disappeared. I think it sounds quite nice - close to where it should be. Some jimi clips would be grand...

[Xplorer]

one more. Fuzz on 9, vol on 8

[Xplorer]

one more with the strat straight in the amp, volume on 10 , presence at zero ( less fizzy )

[VintageCharlie]

Loved the tele clip. I'd say it's there tonewise. Though the strat clip sounds abit harsh/brash despite the presence at 0, at least to my ears. But i'm sure that will go away with further use.
So what did you do in the end - did i understand correctly, that it simply got more and more gain with use - it just got better with break-in - or did you find some sort of error/fault?
If it's just break in, then it's amazing - i'd never would have thought it'spossible that such changes come through break-in alone. Anyway, congrats on reaching your tone-heaven. Now i'm looking forward for some BOG stuff with your 45/100

EDIT: i forgot you're going through a cab sim - the harshness i hear in the strat clip might come from the settings/simulated cab/mic used. Damn that tele/fuzz clip sounds tasty! will have to dig out my fuzz too and do dome experiments, as i haven't played around with pedals much together with the 45/100. What fuzz did you use? I bought a JD hendrix fuzz (a nice fuz and the high gain transistors can be tweaked by a micro pot on the board so you can get them to sound like proper low gain silicon ones) - the blue one and changed the guts to originall GE fuzz face specs with original NKT's (not 275, but the closest substitute i could find spec-wise - i think it was 240 or 214 - they should have had lower hfe ratings, but they had the supposed ideal values of ~120 and 70) and they even have the same casing. Very creamy, thick and wooly and incredibly responsive to volume control settings.

[Xplorer]

Thanks a lot Karlis. Yes, it doesn't sound as good as my real pre rolas.
Now, i'm gonna change this rifa, and see if the old grey RS was too dry or something.
this isn't my tone heaven yet but there's a big potential.
yes, i actualy didn't do anything ! it changed by itself.
my fuzz used there was also a jd blue fuzz, very nice, but i'll tweak it as i said. and i'd be very interested to know more about these nkt !!! because i'm more in this direction too, although my fuzz on the bench, with russian germaniums may have nothing to desire from the real nkt's

i can't resist to post this very badly played bog stuffs, with a very bad recording ( iphone ) , played on a g12h30 75hz at a loud volume. At least It shows this bog tendancy i expected. it's very promising i'd say.

[Xplorer]

just change the 16uf to the rifa 33 uf, and it feels much batter, much more playable.
Also now, all the tubes ( not necessary synchronised ) glow in blue sometimes, depending on the stuffs i play, while before it was mostly just one of them.

i noticed a strange thing : some kind of liquid, under the 0,056uf 450v ac - 1000v dc .... i should perhaps replace it ... ?
there's not much liquid but ...

[Xplorer]

well no .... still sounds fizzy, thin and harsh with a strat when i'm looking for a saturation, break up ...
the fizzy personality could perhaps be the attenuation.
with a fuzz it's great though.
hmm, not there yet + the mA seen accross the 1 ohm resistors have a variation of 5 mA between the hottest and the coldest.

[VintageCharlie]

the machine gun bit at the end of the last clip did sound nice if you take the iphone recording into account. Liquid doesn't sound good - probably best to change the part asap, except maybe it is just some residue from the solder resin?
If it changed so dramatically with burn in, maybe you should give it some more burn in time?
The 45/100 seems to be the thickest, wooliest and warmest of the old marshalls, even when dialing bass to 0 it gets very rich harmonic undertones when dimed to 8-10 on the volume. This is what seems to be missing with your amp at the moment. Doesn't this (huge tonal changes during breakin) actually mean that the issue might be related to the electrolytic caps? Which other components might change their character so drastically?

[Xplorer]

yes, it's missing, but the amp is at leat evolving.
some days ago i could never get such saturation. Now even if it's played through a strat, bridge pickup, and not in a real smooth speaker, it's much better;
But still harsh, thin.

Hey, not even a fuzz on this one, and with a strat !
i changed the 270k sfor some 470k and i swapped the little red 250pf RS ( seemed to be some kind of 350v ) for the usual brown RS 250pf 500v . as i said earlier i also changed the RS 16uf for a new 33uf rifa.

any ideas on how to improve the amp with components swaps ?
Neil said to put some CC 110k on the plates, and increasing the value of the 8k2 to a 18k - 22k value .

the liquid came from the cap, not from some soldering. Just like ... swetting a little.

[Xplorer]

ha ha ! it's a different amp now
but not smooth yet.

this is my tele with the blue fuzz at 9 on 10. This is cool to have a setup that allows to play such amp very loud, just with headphones lol, when the neighbours sleep. But i can't wait to experiment it on a 4x12, it'll be so much better.

[emmjaydubya]

Awesome, sounds killer! The gradual change is pretty dramatic! I can't wait to build one of these...