General Music Chat

well if that thing is dialed in right it could be pushing 70 watts
much higher than my 37 to 42 or so.

I would like to see the schematic,
apparently 6550's are designed for high output.

Don't suppose you know the plate and screen volts for that amp?
was it built to run 6550's?

we are talking marshal right?

ahhh, here is what I found

In the early 1980s, Marshall tube amps sold in the USA were equipped with 6550s instead of EL34s. These amps can accept either type of tube. This was a common modification done to various models in the 1980s and 1990s. Some hard-rock guitarists prefer the sound of 6550s (they break up at much higher volumes than EL34s). Also, traveling musicians have found that 6550s are more rugged than EL34s in guitar amps because the screen grids in 6550s endure less current draw (and thus, less heating) than EL34 screen grids. Be warned, guitar tube amps were not one of the intended applications of the EL34 (actually, no power tube was designed to take such a pounding). Consult a service technician!



The 6550 was developed by Tung-Sol in 1955 [1] originally for use as a servo amplifier. It was used in audio equipment before semiconductor power amplifiers came into use, and continues in production today. It is often found in valve-driven bass amplifiers such as Marshall and Ampeg guitar amplifiers and the Leslie speaker system.

Based on the 6L6 vacuum tube, the 6550 was designed to have higher output power and better stability. It operates with a plate voltage of 600VDC, a screen voltage of 400VDC, and plate dissipation of 35 watts.[2] The KT88, KT90, and 6550, although not identical, are often interchangeable, dependent on external circuit parameters. The 6550's glass envelope was originally wider in the middle than at the top and bottom, but a straight-sided design was later introduced by GE and Philips.

givin this info i would not want a head like this.
you are right It won't sound right till your ears bleed.!

but it will sound good, for as long as you can stand it.!

see, mine is a spec clone of the JTM 45
it runs KT66 which was the European 6L6 , only 27 wats a tube then you subtract 30% and you see I'm way below you.
very much the quieter amp than that 80's monster you have.

once marshall went to el34 that made it a clean amp till you got past 7 on the dial.
adding 6550 probably took the JTM 50 up to almost 70 watts
pretty damn loud!

Semi clean, I would say.
I've heard good things about Fulltone OCD pedal in front of those, or a vintage Tube Screamer. Wouldn't necessarily have to dime it then.

You could mod it to hot rod it, or run an attenuator - both either of those adds extra stress to the innards.

see, mine is a spec clone of the JTM 45
it runs KT66 which was the European 6L6 , only 27 wats a tube then you subtract 30% and you see I'm way below you.
very much the quieter amp than that 80's monster you have.

once marshall went to el34 that made it a clean amp till you got past 7 on the dial.
adding 6550 probably took the JTM 50 up to almost 70 watts
pretty damn loud!

Perspective is still important. The measurable difference between 35 and 70 watts is only 3db (117db vs 120db SPL). So they are both pretty freaking loud.

It's even worse than you know.

The amp is 100W originally and you are 100% correct, it's an early 80's JCM 800 version.
(No Marshall logo but who fing cares>? You don't use that amp for what it looks like...)

I use a Axis Fuzz face and a Sweet Sounds Mojo Vibe only of late.
(my rocket octavia got very sensitive and the wah pedal I just stopped using for some unknown reason.)

But somewhere near 3-4 and it gets uncomfortably loud.

I use 2 Peavey 412S instead of Marshall cabs and I swear I think the stack is moving sometimes, so I put the head on the side and run longer connection cords else I have to watch for trouble.

If the Peavey cabs go boom, I'll just let em go.
But that head is something I would sacrifice my body under to avoid damaging it.

yea you would have to have a big room for that thing. I can't see turning that up at all where I am.
a very different animal all together from a JTM 45

like I said I can turn this about 4 to 7 or so and I don't turn the guitar up past 7 or so.
and I play this in my studio, about the size of a small bedroom.
despite what johnnny7 says there would be world of difference in volume.
wattage isn't the whole story
the type of circuit decides how you might use it.

yea you would have to have a big room for that thing. I can't see turning that up at all where I am.
a very different animal all together from a JTM 45

like I said I can turn this about 4 to 7 or so and I don't turn the guitar up past 7 or so.
and I play this in my studio, about the size of a small bedroom.
despite what johnnny7 says there would be world of difference in volume.
wattage isn't the whole story
the type of circuit decides how you might use it.

Nonsense JCP. It's physics 101. Get out your SPL meter, test it and let us know what you find.

http://www.musiccenters.com/vol.html

Johnny 7, he's just barely smart enough to do a job,
and more then dumb enough to swallow what they
feed him. If somebody don't tell him something he
don't know nothing. I'm gonna call the nursing home and
tell them your down in the rec room on the computer.
Even though playing at the nursing home is probably a
step up from where you usually play, church. Right
Johnny7 huh old man, your old ladies got a wooden leg
with a kickstand on it.
Your real name Johnny is it Neal and Bob or is that what
you do?

yea you would have to have a big room for that thing. I can't see turning that up at all where I am.
a very different animal all together from a JTM 45

like I said I can turn this about 4 to 7 or so and I don't turn the guitar up past 7 or so.
and I play this in my studio, about the size of a small bedroom.
despite what johnnny7 says there would be world of difference in volume.
wattage isn't the whole story
the type of circuit decides how you might use it.

Nonsense JCP. It's physics 101. Get out your SPL meter, test it and let us know what you find.

ok
you may find it on a meter or you may not
but if you don't know what I'm talking about you never played a marshall super lead
and i have never seen any one put a meter on these amps
they just talk about it.
I play them

My DSL opens its throat between 2 and 3. Loudest I've ever set it for a gig was 5.
Definitely not built to be a practice amp, but if I crack it just past where it opens up, it's manageable.

yea you would have to have a big room for that thing. I can't see turning that up at all where I am.
a very different animal all together from a JTM 45

like I said I can turn this about 4 to 7 or so and I don't turn the guitar up past 7 or so.
and I play this in my studio, about the size of a small bedroom.
despite what johnnny7 says there would be world of difference in volume.
wattage isn't the whole story
the type of circuit decides how you might use it.

Nonsense JCP. It's physics 101. Get out your SPL meter, test it and let us know what you find.

ok
you may find it on a meter or you may not
but if you don't know what I'm talking about you never played a marshall super lead
and i have never seen any one put a meter on these amps
they just talk about it.
I play them

It's simple math that is easily tested with a meter. There is a lot of mythology surrounding Marshall amps but they did not change fundamental physics. They are all pretty freaking loud.

http://www.musiccenters.com/vol.html

yea you would have to have a big room for that thing. I can't see turning that up at all where I am.
a very different animal all together from a JTM 45

like I said I can turn this about 4 to 7 or so and I don't turn the guitar up past 7 or so.
and I play this in my studio, about the size of a small bedroom.
despite what johnnny7 says there would be world of difference in volume.
wattage isn't the whole story
the type of circuit decides how you might use it.

Nonsense JCP. It's physics 101. Get out your SPL meter, test it and let us know what you find.

ok
you may find it on a meter or you may not
but if you don't know what I'm talking about you never played a marshall super lead
and i have never seen any one put a meter on these amps
they just talk about it.
I play them

It's simple math that is easily tested with a meter. Marshall did not change physics.
http://www.musiccenters.com/vol.html

this google nonsense,

no one dose a set up with a decibel meter,
there are gain circuits to consider,
anyone who has played guitar amps for any length of time knows that
the degree of payability depends very much on what frequencies your hearing a at what volumes.
gain , preamps all sorts of set ups.
85 watts on a mesa MKIII is a very different animal than 85 watts on a 66' fender twin.
ask any experienced guitar player.

I could set up 3 types amp in a room and I defy you to tell me what the decibel levels are without a meter.

Identical speakers and impedence? Sorry JCP, pure mythological nonsense. Hit a Physics 101 course and get back to me. Be sure to confirm all your findings with a meter. It's a done deal. Don't take my word for it though, email Jim Marshall and ask him...

Is Jim still alive? For some reason I was thinking he'd passed on.