Considering This 1979 Jmp - Please Look At Pics

[paul-e-mann]

I'm looking at this 1979 JMP, the seller is clueless or a bull$h!t salesman, his ad is full of sales pitch and no fact, and said the amp is all original, I do see an fx loop added, I see EL34 not 6550. Can you all please look over the pictures and give me your opinions if its worth buying. My thought is if the fx loop is crap I can replace it with one from Metropoulis if the holes line up and it fits in the space. If I can get a good enough price I might go for it.

 

[Gunner64]

Looks clean. I would buy it if the price was right.

 

[el_bastardo]

Is that really all there is to an effects loop?

You might want to change those bias caps. Besides that, I think it looks legit.*


*I'm no expert.

 

[Gunner64]

Hows it sound? And what's he asking?

 

[Rokinroller]

Old burned out molested junk . Throw that waste of space in that fire behind it in that picture . . . or buy it only for dirt cheap as a boat anchor .

 

[el_bastardo]

Old burned out molested junk . Throw that waste of space in that fire behind it in that picture . . . or buy it only for dirt cheap as a boat anchor .

Why do you say that? What's burned out or molested on it?

 

[Gunner64]

I don't see that. I'd redo the effects loop or remove it completely. Doesn't look like burned out molested junk to me..but I'm not a jmp originality expert. Looks like a fairly clean jmp to me ..and minimally fucked with... What are you basing your boat anchor assessment on?

 

[tschrama]

LOL ... looks great.

Only thing I can see is what looks like a passive loop ( or preamp out?) , parallel bias resistor added, and maybe new PI coupling caps.

But is ooks clean and great. I would buy it if the price was right too.

 

[el_bastardo]

What are you basing your boat anchor assessment on?

I bet it's based on sour grapes.

 

[Gunner64]

Or he's just poking fun at Pedecamp..I'd buy it no question..even if it needed work. Especially if it was under a grand. I just bought a 2203x for $450 that only needed bulging filters replaced..so maybe its one of them deals..I' m all about that.

 

[johan.b]

Probably had a ppimv at some point (see the p.i. caps)and bias range adjusted for EL34 ( good thing from my point of view) and passive loop installed ( never a good idea. Wrong level. Wrong impedance..but you don't have to use it. .) Otherwise it looks Clean to me. .
J

 

[ampmadscientist]

It's obviously not original. Some hack chewed on the PCB....but I guess that's why you can't rely on salespeople to be "historians."
It's a great amp though...not original.

There is something very fishy about that cabinet....is that particle board?
That cabinet (somehow) does not look factory.

I mean: call me crazy but....that looks like particle board (from where I sit).
Maybe I need new glasses.

 

[Gunner64]

A friend had a similar loop installed on his 800 and it was pretty much worthless.

 

[Gunner64]

I wouldn't say the pcb's chewed on..shit replaced from the top is hackish..but none is to the point of fucked up beyond return.. Ampmad makes a point on the cab, it does look like its not original, or has had some kind of overhaul at some point.

 

[el_bastardo]

Chewed on the PCB? WTF are you guys looking at?

 

[Gunner64]

Chewed on the PCB? WTF are you guys looking at?

I was just quoting ampmad..I don't see chewed on either...soldered on from the top yea..

 

[ampmadscientist]

A friend had a similar loop installed on his 800 and it was pretty much worthless.

No the current loop will not provide a boost, because there is no recovery stage. The levels will be all screwy.
The send: will be too high a level.
The return will be too low a level.

Measure the holes on center, then check the dimensions of the metro board....I do not think it will fit exactly....but that is just "eye-balling."

For an effects loop to work:
the send needs to be about 1V P-P.
The effects return level will be 1V...then it will need a stage to raise the level back to normal.
So: the effects loop as is, is pretty useless.

(in USA, effects are "guitar level," about 1 volt in/out) so it won't match a normal effects unit.

"...A friend had a similar loop installed on his 800 and it was pretty much worthless..."

Yup.

 

[el_bastardo]

I was just quoting ampmad..I don't see chewed on either...soldered on from the too yea..

Is it the piggybacked bias pot resistor? The PI caps?

Wouldn't soldering from the top sometimes be beneficial on amps with ancient fragile PCB traces?

This amp is 40 years old. I think sometimes internet experts freak out a little too much over basic repairs done to very old amps.

 

[ampmadscientist]

Chewed on the PCB? WTF are you guys looking at?

I'm looking at the HACK job somebody did to solder parts to the top of the PCB....this frequently damages the traces (typical).
When you see that: it usually means trouble.

But sure, you can still take it apart and put it back to normal.

I think this amp: was originally a combo....then somebody made a new cabinet and turned it into a piggy back head. Just hypothesizing...

 

[el_bastardo]

I'm looking at the HACK job somebody did to solder parts to the top of the PCB....this frequently damages the traces (typical).
When you see that: it usually means trouble.

But sure, you can still take it apart and put it back to normal.

So really, it's not that bad. Got it.