Marshall JMP 2204 Tube change

[tomteriffic]

I've got a friend(!) who is considering selling his JMP 2204 half-stack. It's got 6550 output tubes, which, in general, I haven't been too crazy about in the past. So, I was wondering, how tough is it to change over to EL34's. In addition to re-biasing, I assume that there would have to be some changes to the innards?

Anybody have experience with this?

[JES1680]

The way it was done on mine was an additional resistor was added to the bias circuit to allow it to be biased for EL34s.

I payed a tech to do this many years ago without knowing what was involved. When I reversed the mod recently, I was pretty pissed at what I was charged for adding a single resistor and bias.

[edgar_allan_poe]

I know it is an expense but see if you can get hold of some decent NOS or ANOS 6550s. I have a set of RCAs in my Elmwood and it sounds like god wrapped in a million dollar lottery ticket.

[Turdus]

To do it right, I believe 3 resistors have to be changed. There's also a wire that needs to be relocated at the ohm selector.

Pittman's tube book has some info on this. Gotta be some info online about it.

[Brewmaster]

The way it was done on mine was an additional resistor was added to the bias circuit to allow it to be biased for EL34s.

I payed a tech to do this many years ago without knowing what was involved. When I reversed the mod recently, I was pretty pissed at what I was charged for adding a single resistor and bias.

Nobody ever considers a bench fee when taking an amp to a tech. I wonder why that is?

My bench fee is $50.00 and that covers the first hour. Parts are extra. Bias is included in the bench fee as is cleaning the pots, checking *all* the voltages, and testing the tubes.

I know how to do the mod, it is easy to do but I won't post it. I'm willing to share a lot of info but "how tos" posted on the internet leads to problems.

A tech should do it for about $60-75.00.

[Jimbilly]

I've got some good 30 year old-ish brown base EL34s in my 2204, and all real/old Mullard 12AX7s, I think it's one of the best sounding amps I've ever heard.

If the price is at all reasonable, you should snap it up.

[Brewmaster]

I forgot about this. Two years ago somebody brought me a JMP, forget the year. It had Sovtek 6550 in it and it sounded like crap. I put a set of Winged C KT 88's in it and the amp sounded like a different beast altogether.

I did the same with a heavily modded JMP I bought off this board. I had the amp for a while and when I sold it it had the KT88's in it. Last I heard they were still rockin and the kid is still in love with it.

No mod required for the KT88's.

[kurtsstuff]

I've got a friend(!) who is considering selling his JMP 2204 half-stack. It's got 6550 output tubes, which, in general, I haven't been too crazy about in the past. So, I was wondering, how tough is it to change over to EL34's. In addition to re-biasing, I assume that there would have to be some changes to the innards?

Anybody have experience with this?

I'm looking for a clean and stock JMP 2204 and he should sell it to me

I like em with the 6550's in em

[JES1680]

The way it was done on mine was an additional resistor was added to the bias circuit to allow it to be biased for EL34s.

I payed a tech to do this many years ago without knowing what was involved. When I reversed the mod recently, I was pretty pissed at what I was charged for adding a single resistor and bias.

Nobody ever considers a bench fee when taking an amp to a tech. I wonder why that is?

My bench fee is $50.00 and that covers the first hour. Parts are extra. Bias is included in the bench fee as is cleaning the pots, checking *all* the voltages, and testing the tubes.

I know how to do the mod, it is easy to do but I won't post it. I'm willing to share a lot of info but "how tos" posted on the internet leads to problems.

A tech should do it for about $60-75.00.

I've no problem With bench fee and paying someone for their work. However $200.00 and I provided the tubes is just dishonest.

[Brewmaster]

A tech should do it for about $60-75.00.

I've no problem With bench fee and paying someone for their work. However $200.00 and I provided the tubes is just dishonest.

Yep, that's a rip-off. Guys who pull that crap piss me off.

[Disturber]

I've got some good 30 year old-ish brown base EL34s in my 2204, and all real/old Mullard 12AX7s, I think it's one of the best sounding amps I've ever heard.

If the price is at all reasonable, you should snap it up.

I had old Teslas in my 2104. Played it, it sounded great. I checked the bias and it was at 20mA. So I started to adjust it to run a little hotter. BOOM! One tube just exploded. Scared the shit out of me literally, (I had a SERIOUS hangover too). I ran with the amp to my tech, thought the output tranny had blown. But it was fine, and now sports new tubes - sounds as fine as ever with two new cryotreated EL34's from Watford.

(not to say that your old tubes will blow, reading your post just brought back this memory).