JMP with 6550's vs EL34's?

[Capulin Overdrive]

been trolling ebay for JMP's and seems like some of cleaner ones have 6550's instead of 34's.


so how hot can you bias the 6550's on the JMP's, or more like how high is the plate voltage?


and how much work would it be to get them to run EL34's?



guess i'm scared that the JMP will be like the Deliverance with 6550's? i feel that they don't have enough voltage going to the 6550's in the Deliverance, i seem to like the higher voltage of the Sig-x or the Elmwood M90, or prefer an EL34 amp biased up hot?

 

[Tnjpekar]

I put mine over 52 and she handles it just fine. if anything, the tubes cook a bit faster, but so what.

 

[JTyson]

Changing 6550's to EL34's is not a big deal at all, your only changing a single resistor in the bias supply on the board. If it is a 50 watt, you'll be changing from a 150K to a 220K for 34's. If its a 100watt, It goes from a 15K to a 27K resistor for the 34's. The EL-34 suppressor grid is not tied to the cathode, like the 6550's, you have to re-bias, 6550's run 10V more negative than EL-34's. Cant find my voltage charts for biasing, but I'm sure someone here has that info, ask around, and I'll see if I can find it - Jim

 

[Capulin Overdrive]

thanks guys!


so if i pay top dollar for a clean unbutchered one with 6550's, would i screw up it's value by changing it to 34's?



or should i quite being a pussy and get a 6550 version just to have one?

 

[Plexihacker]

6550s rock in those old JMPs! Slam the preamp with an EQ or overdrive pedal for your distortion. The 6550s will have much more bottom end and won't get all flubby like some old EL34 based amps can do sometimes.

 

[Marshall Law]

for me, I hate 6550's they sound cold to me, I have el34's in all my Marshall's that is the classic Marshall sound, they sound warmer and break up a little quicker, IMO

 

[Marshall Freak]

for me, I hate 6550's they sound cold to me, I have el34's in all my Marshall's that is the classic Marshall sound, they sound warmer and break up a little quicker, IMO

Couldn't agree more.

 

[Greazygeo]

thanks guys!


so if i pay top dollar for a clean unbutchered one with 6550's, would i screw up it's value by changing it to 34's?



or should i quite being a pussy and get a 6550 version just to have one?

You'll make it sound worse.....6550's are great when you get the amp tweaked for them...much bigger and ballsier sounding with 6550's. KT88's are similar in sound but alittle smoother.

You might have heard this in Scott's thread, but here's my modded plexi (similar to a 2203) with 6550's....

 

[JTyson]

I've heard both that blew my socks off. 6550's seem to be a little more { for lack of a better term } mechanical sounding, but this is what a lot of guys who did heavy stuff liked about them. If you decide to change them, it will give the potential buyer some leverage to get you a little off your price, but any decent amp tech could put it back to spec for 50-65 dollars { or less } plus tubes. If he charges more than that, he's robbing you. It would take less than 30 min. to change 1 resistor and re-bias the amp. We are not talking about some huge mod, its probably the least evasive mod you can do to the amp. The 6550 vs. EL34 debate will go on forever, I think each does lean towards a given tone, each brings somthing the other can't to the table, it just depends on the table you like to eat at - Jim

 

[Gainfreak]

for me, I hate 6550's they sound cold to me, I have el34's in all my Marshall's that is the classic Marshall sound, they sound warmer and break up a little quicker, IMO

+1

 

[Digital Jams]

You fuckers better stop looking for JMPs

Bad enough when I miss one 30 minutes from me and Jdud buys a fucking Uhaul full of them

 

[Les Zombie]

i personally like the 6550 better than the el34 in my 2203.
i think marshalls sound awsome with them, i can see how some like 34's better because they will breakup sooner also, you really cant go wrong either way.

 

[thegame]

]You'll make it sound worse.....6550's are great when you get the amp tweaked for them...much bigger and ballsier sounding with 6550's. KT88's are similar in sound but alittle smoother.

You might have heard this in Scott's thread, but here's my modded plexi (similar to a 2203) with 6550's....

http://www.greazyspoon.net/clips/Pl...ge for 6550s without changing that resistor ?

 

[Gainfreak]

6550's also have a cry to them or a whine that I can't stand and they also have a weird attack. They are bass tubes and they almost always need a boost pedal in front of the amp in order to get drive out of them. If you want to hear the cry im talking about listen to Zakks solo in no more tears.

The only way Ive heard 6550's sound great is when someone tweaks the amp. Every old marhsall that Ive heard that had nothing done to them that had 6550's has sounded bad to me but YMMV.

 

[duesentrieb]

To me they sound "hollow" (6550).

 

[Digital Jams]

NONONONONO................

People looking for old JMPs need to look for the 6550 models......yup those are the ones mang.

 

[Plexihacker]

If you want to hear what an old Marshall with 6550s sounds like, listen to just about any heavy band from the late 80's (Slayer, etc.) that used modified Marshalls. Just about every tech I knew in the Hollywood/LA area were using them at the time. Whether that tone is good or bad is up to your ears.

KT77s are about half way between an EL34 and a 6550. A lot of guys are putting these in their amps now thanks to JJ reissuing them. The original GEC/Genelecs have always been outrageously expensive, thus practically nobody used them in Marshalls back in the day.

 

[Greazygeo]

6550's also have a cry to them or a whine that I can't stand and they also have a weird attack.

The only way Ive heard 6550's sound great is when someone tweaks the amp. Every old marhsall that Ive heard that had nothing done to them that had 6550's has sounded bad to me but YMMV.

Do you hear that in my clip I posted? You really need to tweak any amp for different power tubes than what was intended IMO.

 

[Greazygeo]

]You'll make it sound worse.....6550's are great when you get the amp tweaked for them...much bigger and ballsier sounding with 6550's. KT88's are similar in sound but alittle smoother.

You might have heard this in Scott's thread, but here's my modded plexi (similar to a 2203) with 6550's....

http://www.greazyspoon.net/clips/Pl... already anyway, time to change them. YAY!!!

 

[Greazygeo]

I've heard both that blew my socks off. 6550's seem to be a little more { for lack of a better term } mechanical sounding, but this is what a lot of guys who did heavy stuff liked about them. If you decide to change them, it will give the potential buyer some leverage to get you a little off your price, but any decent amp tech could put it back to spec for 50-65 dollars { or less } plus tubes. If he charges more than that, he's robbing you. It would take less than 30 min. to change 1 resistor and re-bias the amp. We are not talking about some huge mod, its probably the least evasive mod you can do to the amp. The 6550 vs. EL34 debate will go on forever, I think each does lean towards a given tone, each brings somthing the other can't to the table, it just depends on the table you like to eat at - Jim

There is actually alittle more to changing over than one resistor. Its stil not hard though...