Help please! 1973 Marshall Super Lead - EL34 to 6550s bias question

[Greg_L]

How would you describe the sound difference between EL34s and 6550s?

From previous experience, I'd say the 6550s are a little tighter, more bass, more highs, normal mids. Cleaner headroom. EL34s are mild in the lows and highs and rage in the mids. Good compression and sustain. EL34s sing better, 6550s punch you in the face better.

For this particular amp, I don't know yet. I'll report back later on that.

I have five other EL34 Marshalls. This is my only 6550 amp.

[Helmholtz]

From previous experience, I'd say the 6550s are a little tighter, more bass, more highs, normal mids. Cleaner headroom. EL34s are mild in the lows and highs and rage in the mids. Good compression and sustain. EL34s sing better, 6550s punch you in the face better.

For this particular amp, I don't know yet. I'll report back later on that.

I have five other EL34 Marshalls. This is my only 6550 amp.

Thanks!
Here in Europe all Marshalls I ever saw, played, owned were equipped with EL34s (and KT66s with JTMs). I always considered the 6550 a great tube for bass amps.

[Greg_L]

Thanks!
Here in Europe all Marshalls I ever saw, played, owned were equipped with EL34s (and KT66s with JTMs). I always considered the 6550 a great tube for bass amps.

Yeah, I think it's pretty well documented that a long run of Marshalls from the early 70s and into the 80s came to the US slated for 6550s. Dealers in the US got tired of warranty work on broken EL34s so the amps were shipped empty and dealers installed their own readily available 6550s. That's the story anyway. My amp has a big sticker on it "USE 6550 ONLY", and the build tag says "USA". It's a Marshall made specifically for the USA market. There is no mains voltage selector - it's US 110v only, and there's a polarity switch, which is disconnected because I've got a 3-wire power chord. There are also four speaker jacks, which was pretty common for US Marshalls. I guess we like lots of cabs. Lol.

And being a guitar player, I love the roar of a Marshall. I'm not a "high gain" guy. I like an AC/DC-type raw garage rock kind of tone. Not clean for sure, but not heavy metal type gain either. Just good ol Marshall rock and roll guitar tone. I hope the 6550s give me a little different flavor from the same type of cake.

[Leo_Gnardo]

Thanks!
Here in Europe all Marshalls I ever saw, played, owned were equipped with EL34s (and KT66s with JTMs). I always considered the 6550 a great tube for bass amps.

I'm sure someone can expand on this: to the best of my knowledge, when Marshall started to become a "thing" in the USA, very late '60s, they started to have their amps imported through an agent. The import agent demanded the amps be equipped with 6550 tubes, I suppose with some idea the bigger, tougher tubes would last well beyond the warranty period and the agent & stores would be seldom pestered with demands for repairs. What really happened was a series of botches & bungles, with overshoots & undershoots in bias, until it got more or less straightened out eventually. IIRC the import agreement ended after 15 years. Then began the Korg/Marshall era. Marshalls started to arrive in USA equipped with EL34's, the way Marshall preferred. That was about the time the JCM800 series started up. In the meantime, some players especially in the USA came to prefer the 6550 sound.

There's more as the history winds on. I'm sure you're familiar with Marshall's abandonment of EL34 in the mid 90's substituting Sovtek wafer base "5881." Which was a good move at the time, as good EL34's were hard to find in manufacturing quantities.

I agree, I like 6550 for bass amps. And I like KT88 even more both bass & guitar. Regardless of my preference, I worked 15 years for an English guitar wiz who preferred 6550 in his 3 or 4 onstage Marshalls. Enough for now.

[Greg_L]

I'm sure someone can expand on this: to the best of my knowledge, when Marshall started to become a "thing" in the USA, very late '60s, they started to have their amps imported through an agent. The import agent demanded the amps be equipped with 6550 tubes, I suppose with some idea the bigger, tougher tubes would last well beyond the warranty period and the agent & stores would be seldom pestered with demands for repairs. What really happened was a series of botches & bungles, with overshoots & undershoots in bias, until it got more or less straightened out eventually. IIRC the import agreement ended after 15 years. Then began the Korg/Marshall era. Marshalls started to arrive in USA equipped with EL34's, the way Marshall preferred. That was about the time the JCM800 series started up. In the meantime, some players especially in the USA came to prefer the 6550 sound.

There's more as the history winds on. I'm sure you're familiar with Marshall's abandonment of EL34 in the mid 90's substituting Sovtek wafer base "5881." Which was a good move at the time, as good EL34's were hard to find in manufacturing quantities.

I agree, I like 6550 for bass amps. And I like KT88 even more both bass & guitar. Regardless of my preference, I worked 15 years for an English guitar wiz who preferred 6550 in his 3 or 4 onstage Marshalls. Enough for now.

There is still a fairly large number of 6550 equipped JCM 800s out there. Those started in 1981 and many of them over here originally had 6550s in them. It's not uncommon at all to see them on the used market. A lot of high gain players prefer the 6550 sound.

I also have a 1979 JMP 2204. This is the 50w master volume predecessor to the JCM 800s. My 2204 is supposed to be a 6550 amp. I converted it to EL34s a long time ago and it's staying that way. It sounds killer.

[Helmholtz]

Yeah, I know the literature.
Own a '67/'68 Super Tremolo and a '68 Super Lead as well as a '66 JTM50. But the best distorted "Marshall sound" (with my then SG with P-90s) I ever had was with a 2203 (JCM800) in a recording studio in the early 80s. Just loved the PU feedback I was getting with that.
No personal experience with 6550s in a guitar amp so far.

(Actually I am more of a JTM45/KT66 guy.)

[drewl]

My '73 1987 is a MKII that was set up for 6550's w/150K bias feeds even though someone had installed EL34's when I got it in the 80's.

I set it up properly like a '69 Plexi and it just roars!

[Greg_L]

Yeah, I know the literature.
Own a '67/'68 Super Tremolo and a '68 Super Lead as well as a '66 JTM50. But the best distorted "Marshall sound" (with my then SG with P-90s) I ever had was with a 2203 (JCM800) in a recording studio in the early 80s. Just loved the PU feedback I was getting with that.
No personal experience with 6550s in a guitar amp so far.

(Actually I am more of a JTM45/KT66 guy.)

Awesome! I love the 2203 circuit...maybe even more than the 1987/1959 circuit for most things. I love P90s too. We probably have mostly the same kind of taste in guitar tone.

My '73 1987 is a MKII that was set up for 6550's w/150K bias feeds even though someone had installed EL34's when I got it in the 80's.

I set it up properly like a '69 Plexi and it just roars!

Cool man!!!

[Greg_L]

Update....

All seems to be going well so far. Nothing has exploded and the amp sounds pretty righteous to me.

Here's some sound samples if you're interested.

1978 Gibson Les Paul Custom - Bare Knuckle Riff Raff bridge pickup
1973 Marshall Super Lead 100 - now w/ 6550s
All tone controls on 5
Ch 1 vol - 7
Ch 1 high input only
Marshall 1960B 4x12 - Celestion G12-65
R144 on axis, 3" off grill, dead center - SM57 on axis, 3" off grill, dustcap/cone seam
50/50 mic blend
No FX or EQ

"Cold" bias - 50%
https://drive.google.com/open?id=1NN...oDlByGsLOwTq5t

"Medium" bias - 60%
https://drive.google.com/open?id=1IC...Zo4KbKj6YyUIB4

"Hot" bias - 70%
https://drive.google.com/open?id=14v...Z9GrQsgolvHeF-


This was done really loud in my home studio. It's so loud in the room I can't really tell the subtle differences with the bias settings, so I recorded them for my own research and thought maybe some of yall might wanna hear it.

[Chuck H]

Definitely 70%

Colder sounds a bit hashy/static-y and not nice in the mids. I don't think you need to go hotter than 70% though. That sounds pretty good.

[Greg_L]

Definitely 70%

Colder sounds a bit hashy/static-y and not nice in the mids. I don't think you need to go hotter than 70% though. That sounds pretty good.

Yeah thanks. I was thinking the medium bias had about the same sound as "hot" and it makes my nerves feel a little better with the tubes being a little cooler. Lol. Thanks for checking it out and all your help.

[g1]

Just for the record, % is with reference to 6550 being a 42W tube? Or the 35W JJ spec?

[Greg_L]

Just for the record, % is with reference to 6550 being a 42W tube? Or the 35W JJ spec?

These are Sovtek 6550WE tubes. The spec sheet says 42 watts, so that's how I did my figures.

[Greg_L]

New question if you don't mind....

I think I might put a PPIMV on this thing. I like using it loud and proud in the studio, but maybe sometimes I might wanna gig with it.

I've put LarMar PPIMVs on other NMV Marshalls, but I'm looking for something less invasive to the board.

The Trainwreck type 3 MV seems ridiculously simple and easy.

What are the drawbacks of this MV on a very loud high power NMV amp?

[Helmholtz]

With Marshalls I prefer the standard pre-PI 2203/2204 type MV.

PPIMVs including the "Type3" have to fight against the NFB, so e.g. presence strongly reduces at lower MV setting.
PPIMVs are fine, though, for amps without NFB like AC30s.

The "Type3" MV is a type of PPIMV and works by loading down and eventually shorting the PI outputs, so I expect it to introduce additional PI distortion.