Another JTM60 1x12 thread/question... (haven't seen this one)

[jbow]

I have a JTM60 combo. The guy I bought it from told me it was in pieces , in a box when he bought it. He told me that he corrected the heating problems and though I have not use it a lot, after about 10 years I have not had ANY problems with it.
I have a lot of amps, by some standards but I'd like to get this one doing a Plexi style clean/hair sort of tone... if I can get there with it. I am NOT interested in getting more gain out of it. It seems that all the MODs I've seen are related to getting different or more distortion out of it.

So, does anyone know any MODs or resources that might help me get that old Plexi kind of dirty/clean out of it? Think, Humble Pie clean. Kossoff. Hendrix (I know, he used Fenders, Sunns, and Marshalls and got his tone out of whatever he used... but I ain't Hendrix, Wishbone Ash: "Vas Dis" clean. Duane Allman, dark clean like the little riff in Trouble No More.

Can this amp be made to produce those kind of tones, or at least more in that direction? I have other amps that will do it but I want this one to do it to if it can.

I collect old Jordan amps and have two of their 2x15 stage combos, they sound great to me. I have an assortment of their smaller combos too, I like them all because my first GAS was for Jordan amps and FWIW, I am always watching for a Jordan Boss amp and Boss Satellite.
Use a Mark V combo.
Fender Vibrolux CR, modded with a switch to add a negative feedback loop.
Valvetech VAC 1x12.
Line6 Flextone III
VOX 1x10 SS/tube combo (I forget the model)
Assortment of oddball small amps, Park, no names, 5e3 and 5f1 clones I built, a Crate Powerblock that (through a Emi Texas Heat) comes REALLY close to that elusive Plexi tone and JCM 800 tone.. according to how you set it).
Crate V-16combo.
POD II
Amplitude for recording
Probably forgetting something.
I mostly play Strats but have a LP, Suhr 2001 LE, Epiphone Sheraton II, Gibson SG 60s tribute, several SX guitars and a few acoustics.
I know... none of this has anything to do with the JTM60 but sometimes people are interested. I mostly play original progressive, Texas and Chicago blues, or blues rock.
I like power chords and riffing. My favorite pedal is a Jordan J-700, it goes from slight distortion to fuzz at full on. I also really like the Tech-21 Comp-Tortion, it never caught on but dialed right it is deadly! I like the Boss DS-1. I have very few modulation type pedals and rarely use even reverb. I like a "pushed" clean best of all but sometimes I like a good strong crunch.

So.. if you know anything I can do to this JTM60 combo. Please let me know. I sometimes wonder if a different speaker would get me where I want to be, a more efficient speaker. I seem to always prefer ceramic speakers though I've never tried a NEO mag speaker.

Thank you and sorry if I gave TMI.. I thought it might help.

[Chuck H]

If you can find and post a schematic that shows complete circuits and operating voltages on the tubes I can try to evaluate the differences between the JTM60 and JTM45. The schems I found were not legible and didn't complete the circuits by showing components that aren't on the boards. Like f'ing panel controls! Terrible schematic.

[Leo_Gnardo]

I sometimes wonder if a different speaker would get me where I want to be, a more efficient speaker. I seem to always prefer ceramic speakers though I've never tried a NEO mag speaker.

Speakers, lots of choices there and the easiest sonic change you can make. At the highest efficiency end vintage JBL's of course D, K and E series. I happen to like Altec 417 in all their variations, sound much the same to me, wonderful. Weber makes their JBL type "California" with or without aluminum dust dome for more or less ping in the 2-6KHz region. EV's are plenty efficient too but not as bright as JBL or Altec. Some of the higher power Celestions hit my ear in the right place, G12-80 another favorite. I recently put a Jensen neodymium-magnet Jet Tornado 12" in a Fender Vibrolux for a customer and that was a treat too, also lightened the amp considerably. Now... how do you audition all or any of these with your amp, that's the quandary.

[Chuck H]

Speakers, lots of choices there and the easiest sonic change you can make...

Now... how do you audition all or any of these with your amp, that's the quandary.

I pondered that question here and tboy was a rock star as usual and set up the "Trade Tent" and made ME the moderator (oops! ) My idea was that members could swap speakers on hand rather than fork out half a grand on new speakers every time they need to find the right speaker for a particular amp. It was a good idea, but it just didn't take. After a couple of years you can probably count the posts at that forum without taking off your pants.

I thought to mention speakers. Then I looked at the schem and saw it was much more of a mid era diode clipping Marshall type amp. Nothing like a plexi. But not so different that some Muntzing and component substitution couldn't get MUCH closer to the right circuit. The JTM60 isn't a "classic" so I wouldn't raise an eyebrow if one were hacked into a pseudo plexi circuit. But the factory schem is a joke. I could do it here on the bench in a blink.

[J M Fahey]

Same here.
Will search for a schematic, although it was probably on this model that Marshall started the f*cking idea of providing NOT the schematic (which is a full, functional, meaningful-to-humans design) but the absolutely crippled .SCH printout straight out of their damned PCB design package, which shows *only* the parts actually inside a PCB joined by routing tracks, and no external connections, which are only represented by wire pads or connectors (about the same) .
So since jacks, pots, switches and tube sockets usually are outside the PCB itself ... they are simply not drawn.
Oh well.
Here I found them (poor quality of course, but somewhat readable) , at our SS Guitar's friend KMG site, the designer of those killer SS tubes:











what you should do is to print all of them, glue/tape them by the edges and with coloured fine point markers join the matching points.
Will end up with a bathing towel sized schematic.
A real PITA if you ask me, but I see no other solution.
Notice that on the top left drawing (won't call *that* a schematic) they provide some kind of map as to where each "CN something" connects.

That said, the amp is quite far from a Plexi/JCM800 and you will need a lot of wire clipping and rerouting (so far somewhat reasonable) and track cutting (a mess) so *personally* I'd pull and junk that PCB and mount a nice eyeletted real Plexi/JCM800 inside, homemade or bought.

You'll need to adapt a few details, such as having bridge tectification instead of 2 diode full wave, bias supply, etc.
No big deal and it does not affect sound.
FWIW bias comes from voltage doubled Op Amp supply but even if you had a transformer with a single HV winding, you can use a capacitive divider like in JCM900 and others.

Personal opinion, you may differ of course, maybe you'll find posts here and there (well, not *here* in MEF ) suggesting Mods to achieve that ... personally I find them a waste of time ... you want a Plexi? ... build a Plexi (or a JCM 800 to have some grind at lower volumes) .

Of course, you'll have to use it *loud* for that muscular Plexi vibe

[Leo_Gnardo]

I pondered that question here and tboy was a rock star as usual and set up the "Trade Tent" and made ME the moderator (oops! ) My idea was that members could swap speakers on hand rather than fork out half a grand on new speakers every time they need to find the right speaker for a particular amp. It was a good idea, but it just didn't take. After a couple of years you can probably count the posts at that forum without taking off your pants.

Short of swapping around a lot of speakers, I'll repeat what I've typed so often I should turn it into a personal sticky: Listen to other guitarists, at concerts & clubs, if you hear something that hits your ear right find out what it is and then you can pursue that. Half the people I tell this to wind up with Vintage 30's. The rest, all sorts of speakers.

For instance, this is how I got to be a fan of ToneTubby: Michael McDonald guitarist Bernie Chiaravalle was using a rig in 2004 including a Yamaha T-100 amp (Soldano designed) and Marshall 4x12 cab loaded with Tubbies. Got a smooth sound that was the perfect complement to Michael's voice. He was kind enough to tell me what he was using & now I know what to recommend to those looking for that kind of tone. Since then I've sold a dozen or two. The green-frame ceramics to be accurate.

[jbow]

Thanks for the schematic!

I have an assortment of 12" speakers, some used some NOS. I have a set of 4 of the Carvin 12s that they blew out about 15 years ago. I think I mentioned that I have a Texas Heat 12 in a cab, I don't know the ohm but I'll try it first. I hadn't thought of that. I have several NOS 16 ohm Webers from back when Ted was still with us.
I'll be trying some different speakers and finish reading the thread to see what else I might try. I've thought of perhaps a different tube in v-1, maybe a 12at7 or something.. I have a few RCA and Mullard 12AX7 or Ecc83 ? I think that's what they call them, one good Telefunken, those are the easy fixes. This amp has lots of PCB so it may not be something easy to mod, especially since I'm looking for tone rather than more gain.
Thanks again!
J

[TarheelTechinTraining]

I had a JTM60 combo for a long time myself. All the schematics are pretty useless, other than finding values. I got tired of fighting it and redesigned it around an 800, though loosely an 800. I used the Pt and Ot and with everyones help now I have a great loud amp. IMHO Marshall made a very cheap amp. Their heart was in the right place but it still sucked.

[J M Fahey]

I got tired of fighting it and redesigned it around an 800, though loosely an 800. I used the Pt and Ot and with everyones help now I have a great loud amp.

this .