Musicians Roadhouse

That is a super cool amp, would love to have one. Hope you get it sorted out.

TubeStack wrote:That is a super cool amp, would love to have one. Hope you get it sorted out.

Thanks Tube.

I am no tube amp guru, just comparing pics it looks like your treble cap is removed from the volume pot, they piggybacked a resistor onto the existing one to make it bias for EL34's, and they did something with those yellow leads on your V1 tube...maybe heat-shrink wrapped some caps or resistors in there. The yellow wire on your input looks like it's on a diferent terminal too. Can't tell if they swapped the negative feedback lead on your impedance selector to the correct one for the EL-34 swap.

michael_dba wrote:I am no tube amp guru, just comparing pics it looks like your treble cap is removed from the volume pot, they piggybacked a resistor onto the existing one to make it bias for EL34's, and they did something with those yellow leads on your V1 tube...maybe heat-shrink wrapped some caps or resistors in there. The yellow wire on your input looks like it's on a diferent terminal too. Can't tell if they swapped the negative feedback lead on your impedance selector to the correct one for the EL-34 swap.

Good information Michael, what would you estimate it would cost to get this back to semi-original condition electronically?

The rest of the amp is so damm nice except for the two holes in the top; I hate to give up on this so quickly.

I am taking the amp back to GC this weekend for their on-call amp tech to evaluate.

I may be able to negotiate some money back from GC or just get a full refund. I am a good customer, and spoke to them already and they seem willing to work with me either way.

Thanks,
Doug

To my novice eye, and the fact I live in California, where everything costs way too much...

As an example, for my local shop to do the job, the restored chassis was a mess, so probably 1.5 hours labor max, plus they replaced the impedance "plug" switch with the modern JCM style switch, which requires grinding/filing the mounting hole to make it fit....more time. I was quoted $125 to do just the switch replacement including parts, so minus that from my total bill of $278 to get an idea of what they did as far as working on the electronics...$158 for parts/labor. Not bad.

One thing that could cost you is if the filter capacitors have to be replaced, the blue cans near the tubes. Apparently they are expensive for parts/labor...about another $150 at my local shop. (they quoted $300 for an old Fender cap job!)

Mine were OK.

Again, this is expensive SF bay area pricing.

Those caps do "wear out" after so many years, so if it needs it and the price is not too bad, it may be worth it for a trouble-free amp for many years.

In my case, the seller advertised it as "all original", "sounds amazing", so when I got it, opened it, and found it had EL34's (with the same piggybacked resistor bias conversion as yours), and the monkey wiring inside, he apologized profusely and said he would cover the cost to fix it once I got him an estimate...or take it back.

He was an honorable guy and refunded $300 from the original price. For once I got lucky and it turned out well.

michael_dba wrote:To my novice eye, and the fact I live in California, where everything costs way too much...

As an example, for my local shop to do the job, the restored chassis was a mess, so probably 1.5 hours labor max, plus they replaced the impedance "plug" switch with the modern JCM style switch, which requires grinding/filing the mounting hole to make it fit....more time. I was quoted $125 to do just the switch replacement including parts, so minus that from my total bill of $278 to get an idea of what they did as far as working on the electronics...$158 for parts/labor. Not bad.

One thing that could cost you is if the filter capacitors have to be replaced, the blue cans near the tubes. Apparently they are expensive for parts/labor...about another $150 at my local shop. (they quoted $300 for an old Fender cap job!)

Mine were OK.

Again, this is expensive SF bay area pricing.

Those caps do "wear out" after so many years, so if it needs it and the price is not too bad, it may be worth it for a trouble-free amp for many years.

In my case, the seller advertised it as "all original", "sounds amazing", so when I got it, opened it, and found it had EL34's (with the same piggybacked resistor bias conversion as yours), and the monkey wiring inside, he apologized profusely and said he would cover the cost to fix it once I got him an estimate...or take it back.

He was an honorable guy and refunded $300 from the original price. For once I got lucky and it turned out well.

Thanks Michael,

I am taking the amp back to GC this weekend for their on-call amp tech to evaluate.

I may be able to negotiate some money back from GC to put it back to original, if not, I will probably just go for a full refund.

Thanks,
Doug

So how did it go? Keeper or returned?

Update 12/26/12

It's been a crazy month for me buying and retruning amps. I have not owned a Marshall JMP in over 30 years and this past month, I have owned four JMPs and returned 3 JMP's (Thank you GC for your return policies).

1st) A JMP-1 liked the JMP-1 alot, but for a few hundered dollars more I could own a vintage JMP (Status Returned)
2nd) A 1979 JMP 50w Master Lead Combo, loved the look, but too modded and sounded bad (Status Returned)
3rd) A 1977 JMP 50w Master Lead Head, nice shape but an earily '77 model without cascading gain, ie no gain, (Status Returned)
4th) A 1981 JMP 50w Master Lead Combo, mint conditon, 6550's, all original, sounds excellent (Status a Keeper)

Future, I still want to purchase an original late 1977 or 1978 JMP Master Lead Head at a fair price.

I will post some pictures on the 81' combo in a new thread.

Thanks for the interst, Love these old Marshalls

I second the idea of having an amp tech check it out - make sure you check out the tech first!

Right on Glad to hear you found "the one". Sad that so many of these old amps got butchered.

What speakers does it have in it?

michael_dba wrote:Right on Glad to hear you found "the one". Sad that so many of these old amps got butchered.

What speakers does it have in it?

Original Celestion branded G12-65's that look brand new.

GuitarBuilder wrote:I second the idea of having an amp tech check it out - make sure you check out the tech first!

Today I left the amp at a shop that I trust and have done business with before.

They have an amp tech that is good and is friends with a few people that I work with so I trust the guy.

The amp has Groove Tubes in it and I may swap these out with something better. The shop swears by JJ's. Guess I will wait and get the update.

Thanks for your help.

Doug