Marshall tube question

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I have exactly the same head as you (in Purple)
When I eventually get around to getting some time - I will be looking at replacing the 5881s with EL34s (which should have gone in the early 1990s JCM900s but there was a problem I do believe with availability so they built a 5881 model)

Not quite sure what I have to do to put the EL34s in though...
 
the tung-sol data sheet describes the 5881 as-

"the 5881 is the electrical equivalent to types 6L6 and 6L6G except the plate and screen dissipation ratings have been increased approx. 20% It embodies a complete mechhanical redesign which results in greater resistance to shock and vibration. the use of treated grids and anodes greatly increases its overload capabilities and thereby provides desirable improvement in continuity of service. the addition of a low-loss barrier type base will provide obvious advnantages in certain applications"

so the 5881 seems to be a healthier version of the 6L6, and if it is going in a marshall, seems tobe a good idea.
 
I would personally go for EL34s unless you prefer the more American cleaner sound.

What sort of music will be going through them?
 
6L6 types can be very confusing, especially since you have to distinguish between the "old" 6L6 family tree, and the "new" one.
Main old 6L6 types (not complete list):
6L6 (metal)
6L6G (large coke bottle glass)
6L6GA (smaller coke bottle glass)
6L6GB (straight-sided glass)
all the above have basically the same "book" ratings, then:
5881 (small bottle, industrial ruggedized/improved 6L6 as noted in a previous post)
6L6GC (VERY rugged, higher ratings compared to 5881)
Plus further changed/improved types like 7581, KT66, EL37, etc.

So for NOS note that the 5881 is more rugged than "standard" 6L6 types, but less so than 6L6GC.

However, for new production, lots of extra suffixes, etc. have often been added to standard or inferior types with little rhyme or reason. The main contemporary tube branded a 5881 is the Sovtek type, which is reasonably more rugged than the cheap "standard" 6L6 types from China and former Soviet manufacturers (some of which have been erroneously called 6L6GC at different times, and by different distributors).

But there are also some contemporary "GC" types which approximate the "old" GC types, and those can be more rugged than the contemporary (Sovtek) 5881. Confused yet?

Anyway, to attempt to answer your question, the stock 5881 is probably more rugged than the cheapest new 6L6 types, but the better 6L6GC types are probably as rugged or more so than the Sovtek 5881, so you would likely be safe with one of these.

I'm not really sure of the origin of the specific "6L6GCR" you mentioned. A web search of this number turns up a bunch of links to standard Chinese types that I personally would probably NOT use to replace the Sovtek 5881.

I also second the advice to use the duncanamps TDSL, although it mostly refers to the data sheets for the NOS types.

Hope this helps.
 
[quote author="rodabod"]I would personally go for EL34s unless you prefer the more American cleaner sound.

What sort of music will be going through them?[/quote]

Hard rock I guess, but he plays fairly clean most of the time to make his notes stand out in the mix
 
Maybe you should stick with the 6L6 / 5881 valves then.

The EL34s give you more of that "brown" sound because they break up fairly early and nicely.

The 6L6 / 5881 are a bit more solid and might be better suited. It just depends on taste.
 
I had my JCM900 4100 modded from 6L6s to EL34, and I think the tone is much better. I always found 6L6s (at least in this model) to be a bit harsh. I play heavyish type rock I prefer the sound with the EL34s.

But as rodabod said, it's a matter of taste.

And shouldn't this be in "The Lab?"
 
You can put EL34's in a 5881/6L6 circuit, but the output transformer impedance will be off. A lot of that Marshall sound is in the output iron. So you will have a set of EL34's that sound like a Fender amp.

I have the Marshall book and remember reading something about them exporting 5881's instaed of EL 34's because they were having so many problems with tubes popping in the US, for reasons I forgot. Maybe mains problems or the lack of availibility of good Mullards. Maybe someone with the book can re read and make a post on that. I remember their rep took a hit because of the 5881 thing, which led to the downward spiral.

The 5881 is a killer tube if it's the old NOS stuff. I believe that's what Keith Richards runs in his favorite Bassman. But he has a ton of amps so you never know what you are hearing. People give him amps on a daily basis. The early Bassman's were choke input, BTW, which gives a bit more sag due to dcr/poor regulation.

Never mind. That was a 6550 Marshall thing. Not 5881. :oops:

cj
 
[quote author="CJ"]
I have the Marshall book and remember reading something about them exporting 6550's instaed of EL 34's because they were having so many problems with tubes popping in the US, for reasons I forgot. Maybe mains problems or the lack of availibility of good Mullards. Maybe someone with the book can re read and make a post on that. I remember their rep took a hit because of the 6550 thing, which led to the downward spiral.
[/quote]
(quote edited with author's own correction)

According to the Groove Tubes book the distributor was replacing the stock EL34 with 6550 just on the basis of mechanical strength. Supposedly they didn't even rebias the amps for the 6550 at first.
 
I think that's it. The trauma from shipping to the US was killing the 34's.
People over here wondered why their amps sounded different.

Thanks on that.
 
I personally like the sound of a good 6L6gc a funny point about the 6550's is that if you look at an original 6550's internal structure and a us made 6CA7 (el34) they look pretty darn Identicle. that is my absolute favorite in a marshall 50 is the sylvania 6CA7 Wil

Wilebee
 
OK I read last night that another reason for exporting the 6550 to the US was that it was easier to get that tube over here vs the EL-34.

It looks like Marshall amps were changing all the time, not just tubes, but transformers and other components, so the history is quite involved. I think that most of the sound comes from those 4 x 12 cabs with the crunchy 30 watt Celestions. I built the varoius versions on my proto chassis, plexi this, .001 cap that, and had to go rent a Marshall cab from GC for a day to get that sound, otherwise it just sounded like a Fender, with a bit more crunch from the EL 34's.

The first Marshalls were based on the early Fender bassman, and went from there. A 2 ohm feedback resistor instead of 16 ohms, tube rectifiers for most models, running out of phase, EL 34's and different output iron and those speakers seem to make up most of the difference.

Don't forget that the early versions had 6L6 and KT66 tubes, like the Bluesbreaker and JTM 45.

KT stands for "Kinkless Tetrode", an attempt to get the tube curves straightened out between the class A > class A/B transistion zone.

MO stands for Mullard-Osram, a division of GEC which stands for General Electric Company, an English branch of G.E.
 
> KT stands for "Kinkless Tetrode", an attempt to get the tube curves straightened out between the class A > class A/B transition zone.

No, the kink is at low plate voltage, and particularly at low plate current. This is not really an interesting area for Power amplifiers: they must swing to low plate volts at high plate current.

It has some slight effect with very oval loadlines, meaning speakers near bass resonance.

The main point of the KT line was so they did not have to pay RCA for Beam Tetrode patents.

[/i]if you look at an original 6550's internal structure and a us made 6CA7 (el34) they look pretty darn Identical.[/i]

Several different tubes were sold as 6CA7; some not much like Euro EL34s.

I think most of the key patents ran out by the 1950s. Anyway everybody was buying tubes from each other (an RCA or GE distribution catalog offered about 99% of all types ever made, but surely they never actually made that many types). Most types were minor variations of others. And TungSol was challenging the market with new types like 6550 (and 6336). So I think tube production "rationalized" in the 1950s.

In the same period, Ford Motor Company made well over a dozen "different" engines for Ford, Mercury, Edsel, and Lincoln. The "unique" engine was a feature of the Edsel. But there were just 3 basic blocks (2 blocks covered 90% of production) and about 5 different pistons. Mix-n-match, you get 239, 256, 272, 292, 312, 383, 410, 430, 462, 332, 352, 360, 361, 390, 406, 410(again), 427, and 428. Looks like a lot of engines, but they are just a few different parts stuck together in combinations. Contrast that with GM, where every division had its OWN truly-unique engines from the 1920s through much of the 1970s. GM later shifted everything to the Chevy and Olds engines; the tube companies did the same rationalization decades before. If a car idles and pulls well, if a tube idles warm and makes its power, nobody cares the exact shape of the torque or current curves or whether it derives from KT or 808/6L6 patents.
 
[quote author="CJ"]OK I read last night that another reason for exporting the 6550 to the US was that it was easier to get that tube over here vs the EL-34.

It looks like Marshall amps were changing all the time, not just tubes, but transformers and other components, so the history is quite involved. I think that most of the sound comes from those 4 x 12 cabs with the crunchy 30 watt Celestions. I built the varoius versions on my proto chassis, plexi this, .001 cap that, and had to go rent a Marshall cab from GC for a day to get that sound, otherwise it just sounded like a Fender, with a bit more crunch from the EL 34's.

The first Marshalls were based on the early Fender bassman, and went from there. A 2 ohm feedback resistor instead of 16 ohms, tube rectifiers for most models, running out of phase, EL 34's and different output iron and those speakers seem to make up most of the difference.

Don't forget that the early versions had 6L6 and KT66 tubes, like the Bluesbreaker and JTM 45.

KT stands for "Kinkless Tetrode", an attempt to get the tube curves straightened out between the class A > class A/B transistion zone.

MO stands for Mullard-Osram, a division of GEC which stands for General Electric Company, an English branch of G.E.[/quote]


The The JAN-Sylvania 5881 JAN-Philips 6L6WGB is a classic tube with classic tone. This stubby bottle, black base 5881 tube is the same tube occasionally found labelled JAN-Philips 6L6WGB. Our stock is in JAN military boxes date-coded 1979 to 1980.

Heavy bottom, very faster, warm and taut in the middle and completely purifies sliky / seidige heights. The distortions somewhat in former times, but much controls and very softly. The old NOS Tung Sol is somewhat better.
 

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