JTM 45/100 - Build story

[Xplorer]

Thank you.
about the transformer, it follows the diagram from marstran and yes it is connected to the ground : the purple wire going to the fuse in the chassis, which is grounded on the other side by a screw soldered to a lug touching the chassis. so it has its own individual lug.

i'll go get a new volt meter right now, cheap ( till i get the fluke from my friend ) and verify the solder joints. But except for just one or two connections, i used a very high quality solder tin from france, i really liked it cause it melts nicely, and sticks very well. I waited long enough to be sure that it would melt and stick with the turrets and connections. The excedent of solder is just to make it prettyer.

BUT, yes, it might have a problem somewhere so i'll check these points anyway. i'll measure the B+ with a connection on the B+ from the rectifiers, and from the chassis, with the volt meter. DC !

[shakti]

Also make sure you have the diodes in the right direction. IIRC you're using NOS diodes, which means you can *probably* put them with the same orientation as in old amps. But the new production diodes that look like these old ones, actually are the opposite, so if you try to put them with the "hat" directed the same as the old ones, they are actually oriented with the anode and cathode swapped 180 degrees.

[Xplorer]

thank you ! i bought a new cheap voltmeter, sufficient for this operation hopefully ( but really, it's crap, i'm waiting for the fluke ) , and it works !!
i'll show you some pictures of the diodes which have a drawing of the diode schem and orientation on it, it seems good ).
Right now the B+ measures about 504 volts.
And measuring the DC voltage accross the 100k is right now at 30 volts, decreasing, it started at about 300 volts.

Yes !
so i wonder why the other voltmeter got broken, even if i set it on AC voltage 600. maybe an amperage tolerance on this setting that wasn't acceptable, don't know ...
ok, 29 volts now ..
i'll can endly work for my client while it's reforming ! lol. This is the kind of thing that you don't want to rush but ... you don't have the patience to wait and your whole concentration has the amp for a target

Thanks !

[shakti]

Good to hear!

Can't wait to hear reports! A lot of people have reported that their 45/100s were very stiff sounding at first. I wouldn't say that mine was any worse than my other amps in that respect, but new amps do definitely need some time to settle in and sound their best.

[Xplorer]

Ok. And do you think i should wait a lot of hours before setting the volume above 6,7 ... ?
23,5 volts by now ... i'm noting voltages and hours ha ha. if it's a constant curve, it should be under 3v in about 5h30.

[neikeel]

Ok. And do you think i should wait a lot of hours before setting the volume above 6,7 ... ?
23,5 volts by now ... i'm noting voltages and hours ha ha. if it's a constant curve, it should be under 3v in about 5h30.

It is only the preamp can tha tis reforming now. The RIFAs will be done. Some of the old caps need overnight.

My 45/100 was slow to settle - took quite a few hours to get 'the sound'.

[Xplorer]

yeah, it got at 19 volts, then back to 21 volts, now 19 volts again.

Are you saying that for now it operates mostly on the preamp can, and later the rifas ? i've got confused by what you said.

[neikeel]

No....the new RIFAs reform really quickly.

A 50 year old RS can will take all night, sometimes they do not reform fully and you have to decide whether to junk it for a new one or accept that it is not quite up to scratch.

[Xplorer]

Well ... i hope that it isn't going to happen to me but .. it went down to 15 - 16 volts after 7 hours but after 9 hours now, it even increased agai to 17 - 18 volts !! and now about 16-17 volts.
( but earlier in the day, it went down to 19 and later increased again to 21 volts, till it went down to 15-16 volts recently.
acting by steps perhaps ...

from which voltage can the amp be considered to be playabel ? really only 5 volts max for the reforming ?

[Xplorer]

indeed ... steps ! now it got down to 14 volts !
something close to a sinusoïdal curve going down.

[VintageCharlie]

The wall voltage isn't extremely constant either and i suppose the chinese meter at hand isn't the most precise one either. Go to sleep and fire up the amp tomorrow and PLEASE, make some clips!
The amp looks fabulous, one of the best builds i've seen on the site (yeah, some joints seem a bit rich on solder, but as long as the mechanical connections are good, i don't think it should be aproblem).

[Xplorer]

Thanks Karlis !
yes, i prefer a bit more tin on the connections, for more metalic contact. the thing isn't really blobby or at the surface ... it goes inside the turret and melts everything together , stronger. Old ones are solid but they seem a bit too fragile to me.
i hesitate to stop the reform of the caps tonight, and restart tomorrow cause i don't want to burn while i'm sleeping .... !
and i calcularted that it should require 15 to 20 more hours actualy ( or more ) to end the process.
it's at 13,5 volts by now.
Sure ! i'll make clips when i'll have a mic someday, or i'll use whatever i have. with my superlead the pre rolas sound really good ! even attenuated. But i can't play loud, though i did it once, and the whole flat moved !! and i was frightened for a few seconds when i played the intro of Stone free at max, with the fuzz at max !! unattenuated ( but just with only one speaker, the three others being basicaly replaced by some resistors ) . For sure the cat ran away in the house like crazy ! lol. perhaps the loudest sound experience i ever had

[neikeel]

You must try a full stack cranked and unattenuated on a big stage - nothing quite like it

[Xplorer]

Sure ! And i can only admire even more these guitar players who ran the show this way back then, because mastering all that power .... wow, this isn't easy !

Ok, i've let the caps to get reformed this night, and i didn't burn .. ( Dom told me that anyway there's just a little current in it, no heat, just big voltage ) . And it went down to 9 volts. It's very long but i'll still wait anyway.

[neikeel]

Yes patience!
I have had a couple of amps stall at this stage and seen te voltages go up again!