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Anyone Try a Marshall JMP with Bass?

chaosMK

chaosMK

May 26, 2005
5,549
1,675
Albuquerque, NM
Disclosures
Too much hip thrust
#1
I decided to plug into my drummer's JMP this last practice. A while back I had unearthed it during an archaeological mission in his garage and when I saw it used 4x 6550's I was inspired to get it fixed for him. All it needed was a replacing a "milky" power tube. This amp was so old it had Made in Hungary Tung Sol 12AX7 tubes and GE in the power.

Anyway... kind of a cool head for bass! Power was sufficient for my "light rock" band. I had to dial away a TON of mids but aside from that I liked the gain structure, nice match of headroom and touch sensitivity. Just a dash of that barky sound when diggin in. By itself it still had a bit of Marshall voicing (a little harsh) but in the mix it blended well, quite warm actually.

Anyone ever play around with one of these?

The JMP looked something like this but more aged:

MarshallAmp.jpg
 
#2
Hi.

In my late teens/early 20's my rig was a JMP1959 and JCM800 412 & 215 cabs.

Very good 60's/70's period correct bass tone.

Heavenly with the channels jumped.


With 6550's in one, do make sure that any Marshall amp is actually modded for them.
6550 was never the choice of power tube for 100W Marshall (only EL34), just the US importers way to weasel out on the tube warranty.

Regards
Sam
 
#3
I have a Bugera 1960 which is much the same amp I think? There's a thread about them here somewhere. The "Infinium" version (self biasing) has the channel jumpered mod AND the channels in series (AKA Randy Rhodes) mod built-in as well as a master on the back. Fun amp with an efficient cab or two, I'm thinking of using it for a Rolling Stones tribute I'm trying out for tonight :) .
 
#5
The trick with the real 2-input ones (old JMP or newer JCM 800) is to plug into the low input!

This skips the first tube stage and gives you a totally clean preamp even with the pre-gain dimed, and sounds really nice for bass.
 
#6
I played in a dual-bassist band for awhile where the other bassist (the "lead" bassist!) played through a JMP- he took full advantage of the gnarly gritty mids and it was a great compliment to my deeper tone (400+). We were super loud, but at more reasonable volumes it sounded surprisingly sweet, with just the right mid saturation through a 2x15. I also have played bass through an old Traynor Super Bass (IIRC) at our practice space which is a JMP clone/variation as I understand it and it also sounds super sweet!
 
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#7
One of my amps, the Science Hellhawk is a Marshall Super Lead clone, similar to that JMP. Which is based on the Fender 5F6-A Bassman circuit. I've played bass through it through my 8x10 and it sounded good and punchy but a bit too trebly. If you're going to end up with that amp, modding it to Super Bass specs from Super Lead would be a great idea.
 
#8
I have played with a JMP Master Lead 100 through an 8x10 and a 70 SVT and 8x10 together at the same time. Sounded awesome.
Also Marshalls did come with 6550s. I have a 74 Marshall Super Bass that came with 6550 tubes and I have a 73 Super Lead that is a El34 amp.
 
#9
I've used the JMP in the past, using the Bugera 1960 as the guy above, with a Trace Elliot Stack. Really fantastic amps for bass both of them, they may be quite different in terms of quality with guitar but you're getting the same essence with both on bass. Clean you'll get a fantastic warm sound, just saturated is really lovely, and gritty with new rounds gives you more power than you could ever reasonably want, especially with a pedal. You gotta have an efficient cab setup, but if you do it really will do the job well for rock.
 
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#10
Whoever e-mailed Alex about a Hellhawk for bass, ask about getting the Super Bass's tone stack instead of the Super Lead's in order to have your amp voiced for bass if you're going to get one. I'm starting to think about having that done instead of getting the 200 watt HiWatt/Matamp clone he makes.
 
#11
I've used JMP Super Bass amps for years. Love them. The last 2 Exciter records featured my 2 1973 SBs. Live these days, I'm using VBA400s, but in the studio it's always the Super Bass amps.

Cheers!
 
#13
After more experiences with the JMP for guitar, neither of our guitarists like it! It's just a little harsh and thin (except extremely loud) for our taste I guess. Maybe it was designed to warm up around massive outdoor stage volume? Legit as a bass amp though, and kind of unique or at least different from most amps I've played.
 
#14
chaosMK said:
After more experiences with the JMP for guitar, neither of our guitarists like it! It's just a little harsh and thin (except extremely loud) for our taste I guess. Maybe it was designed to warm up around massive outdoor stage volume? Legit as a bass amp though, and kind of unique or at least different from most amps I've played.
Click to expand...
If the power tubes are 6550s instead of EL34s, that could be a big reason for it not having the guts a Marshall should have for the guitarists. Non-MV marshalls start to Overdrive around 4 on the volume knob, that is insanely loud though.
 
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#15
chaosMK said:
After more experiences with the JMP for guitar, neither of our guitarists like it! It's just a little harsh and thin (except extremely loud) for our taste I guess. Maybe it was designed to warm up around massive outdoor stage volume? Legit as a bass amp though, and kind of unique or at least different from most amps I've played.
Click to expand...

Is the amp in the picture in the first post the actual amp you're talking about?

Cheers!
 
#18
Seriously, if the power tubes are GE they're more than likely to be 6550s. Marshall don't run on 6550s, EL34s just weren't surviving the import to the US so American distributors had Marshall change the bias circuit for American tubes and when the amps arrived they were loaded with 6550s. It was just a corner cutting measure because customers were constantly using their tube warranties on new amps.
 
#19
chaosMK said:
It's not the actual one but it looks just like it. The one we have is in way worse condition. It was in our drummers garage for nearly a century.
Click to expand...

Ah, ok. Just so you know the picture shows a 50W Master Volume (likely 1976 based on the cosmetics) amp - model 2204. Does the amp you actually have have 2 or 4 inputs on the front, and is it 100W (4 power tubes)?

Cheers!
 

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