Help with tubes please!

[Cack]

Right, I recently bought a Marshall JCM900 Dual Reverb (100w combo) (for €300). Its in perfect condition apart from the tubes in it are a bit worn. Can anyone tell what preamp and power amp tubes they would recommend for a high-gain puchy kind of distorsion (I mostly play metal). Keep in mind I don't want to be spending too much on them.
Also I have another little question, On the back of the amp there is a swirch that changes it from 100w to 50w, what's the pupose of this???
Oh yeah this is my first tube amp as well!

Thanks,

[Foolius Maximus]

Re: Help with tubes please!

Paging Pete and John, paging Mr. Pete and Mr. John- Hey cack, I believe that amp uses el34 power tubes- I'm not real sure what brand would be best for that amp but I'd suggest Electro Harmonix or Sovtek 12AX7's for the preamp section- I use them both and are very happy with them- Neddi

[Cack]

Re: Help with tubes please!

Hmmm, as far as I can see, there are 2 EL34's and two 6L6GC's in it. I guess the previous owner was messing around with it..... Are the preamps those metal tube things beside the power amps?
Right at the moment the distorsion on it is a bit weak, this is proably to do with the tubes being 6 years old... Will buying new tubes give me a stronger punchier distorsion or am I wasting my time and money?!?! Also, send in some more tube recommendations! The guy from thetubestore recommended Electro Harmonix 6L6GC's for metal.

[Cleveland Metal]

Re: Help with tubes please!

Well maybe Pete will know how they have 6L6 AND EL34 in the same amp... I always was under the impression that they had different pin outs. 6L6s are good for metal as well as EL34, depends on your taste.

I'd say you need to get that amp to a tech to see what the previous owner had done to it BEFORE sticking any power tubes in it... That does not sound right to me having both of the styles of tubes in the same amp...

As for more tube suggestions, I've been playing extreme metal (Slayer, Iced Earth, Coroner, Savatage, King Diamond, Sepultura etc) for 25 years, and that's what I use in my CAE3+se preamp and my VHT 2150 amp, and every marshall I've owned witch have been many. I used most brand of tubes and that's what I would use, Svetlana.

Electroharmonix power tubes are crap.. But, hey, he's a salesman. I'm sure he's selling exactly what he, umm you need...

Yeah, the metal things are RF shields that twist over the 12ax7 preamp tubes...

[Cack]

Re: Help with tubes please!

Thanks Cleveland you've been a great help. What preamp would you recommmend, as I understand that controls the gain etc. Have you ever had a JCM900 and were u able to get decent distorsion out of it? I am gonna get it serviced but 1st I want to get new tubes so that they can be biased while the amp is being serviced. Which model of svetlana's was it you said were good? Oh yeah and apparntly the JCM900 came with 5881's which are a varient of 6L6's aren't they? (thats if you bought it new)

Thanks

[ December 10, 2002, 03:54 PM: Message edited by: Cack ]

[Cleveland Metal]

Re: Help with tubes please!

Well, like I said in my first post which you must not have really read... [img]images/icons/frown.gif[/img] I've owned several, two that were brand new (came with EL34s in mine)... I also told you things what outboard things I used to get good crunch out of them...

Umm, I also mentioned that I felt the "chinese" 12ax7 tubes from the tubestore were easy to get, cheap and the best sounding tube. The chinese 12at7 or 12au7 "SINO" brand tube for the driver tube is available at the tubestore too.

Don;t put the power tubes in till the tech checks it out... You wish to let him decide what the amp is set up for before buying the power tubes.

Svletlana EL34 is "my" choice, and they only make one style of EL34.

Maybe read through my earlier posts to you here, I think you may have missed some stuff, hehe.. [img]images/icons/smile.gif[/img]

[OklaStrat]

Re: Help with tubes please!

I'd look on the tubes to make sure they were EL34s and 6L6s or 5881s or whatever - they should have printing on them.

Only difference other than bias on an EL34 vs a 6L6 variant is pins 1 and 8 have to be tied together for an EL34.

Interesting aside... my mesa single recto, which uses 6L6s and has no el34 switch, already had pins 1 and 8 soldered together. [img]images/icons/grin.gif[/img]

It is possible to run EL34s and 6L6s together if they are matched for current draw - bob at eurotubes sells sets like this.

El34s have more mids, and looser lows than a 6L6. 6L6 tubes tend to have better/tighter lows, slightly scooped mids, and slightly brighter highs.

I prefer EL34s, but I don't play real heavy music either. I need to get a schematic for my single recto so I can put a bias pot in there [img]images/icons/grin.gif[/img]

Pete

[Troy from VENTT]

Re: Help with tubes please!

That's so wierd that you say that... Now keep in mind I'm a total dummy when it comes to tubes (As with MOST things), but I noticed a DRAMATIC improvement in Low End Tightness when I went from the stock 6L6's to Svetlana EL34's. Now I DID notice a slight increase in Mids also though.

[OklaStrat]

Re: Help with tubes please!

were the 6L6 mesas? mine SUCKED in the single recto... the NOS 5881s I put in there (which are a variant of 6L6s) sound about 3 times better.

All other things being equal, a 6L6 tube should have a tighter bass and glassier highs, with a scooped midrange. The EL34s should have a more pronounced midrange and looser bottom end... at least my VHT, Univalve and Dual Recto behaved that way. I wonder if your 6L6s were worn when you replaced em, or just craptacular to begin with.

The 6L6s also have a tendency in my experience to stay tighter longer, and not overdrive as fast as an EL34. Again, just my opinion. [img]images/icons/grin.gif[/img]

Pete

[Cleveland Metal]

Re: Help with tubes please!

Pete, I would agree with everything in that last post totally...

[Cleveland Metal]

Re: Help with tubes please!

I believe you asked this question on the old board, and I'll also re-answer your bias question too, and the question about getting "crunch from power tubes"...

And welcome to the most excellent world of tube amps...

_____________
Yes, you will have to bias any amp when you change power tubes (not preamp tubes). PARTICULARLY THAT AMP... When I bought a pair of 4100 JCM 900s brand new and tubed them, the bias on both was so far off they had to change the bias circuit resistor to get it to adjust in spec. Due to the crappy tubes Marshall initially used in it.

Biasing is important. If it's running cold, the amp will sound weak, if it's too hot, it will kill tubes quick. You want that happy medium for the most part. I personally, like my misc amps biased a bit hot.

So yes, get it biased...

Note: MESA amps are the only ones that aren't biasable. And that "can' be a problem...

As for easy to attain and reasonably priced tube... Tubestore.com is a good place... There are others, I use them a lot though.

My personal preference would be Svetlana EL34 Power Tubes for that amp, and most other amps really. I did also use Teslas in my 900s for a bit and they really weren't "bad".

"Basically", power tubes won't give you any noticable gain in crunch or distortion.

Some of the Groove tubes that are rated low will go into saturation a little lower in volume. But that is sort of a flabby saturated eric clapton-ish distortion. Not an edgy, crunchy metal distortion.

Some higher rated ones will sound tighter with more edge, and not saturate as much. More metal like.

Power Tubes will however, affect tone somewhat, and that would be a personal thing. Different muances that you "would" hear in the tone, is usually more noticeable when the tubes in the amp are saturating at high volume levels. That's when you'll hear the true character of the tubes I think. That is what you hear before you go deaf at full volume of a 100 watt Marshall, haha.

Again, I liked the Svetalanas mostly and the Teslas somewhat in the 900s...

Preamp tubes can have a noticeable difference in the crunchability of the amp. The Chinese 12ax7 preamp tubes at the Tubestore are also my choice of tube for that app. They are easy to find and cheap to get. DON'T get the new Svetlana 12ax7s. They are noisy, popping, humming crap...

There are others brands that work ok, and many like the EH 12ax7 that are out now.

If you want more crunch out of that amp. I have to say, I feel that they are they are somewhat anemic out of the box... They can be coaxed into a good sound, and I was often complimented and quized heavily on my very nice sounding 900s...

Crunch stuff for the JCM900:
I used, a cheesy Nady 201 wireless around that time and it had a hotter output than the cord did. That helped give me a lot more edge in the sound over using the cord. Umm, a EMG PA-1 preamp would be a good thing to try also to heat up the front end. Although that worked, the amp didn't like any traditional booster or distortion pedals... Quite weird...

I also used 31 band EQs and also an old Rockman EQ at different times in the loop. Both were quite an improvement and would be somewhat mandatory in my eyes to have.

I sometimes used a BBE422a in the loop also. That was a love hate thing for me... I ended up not using it in the end.

That output Mode Switch you're asking about switches the amplifier from high to low power
output. The “low” setting changes the output
to 50 Watts on 100 Watt amps. The “high” power setting gives “pentode” operation for the full rated 100 watt output. It does not turn off any tubes, it change how they work. AND will change the tone somewhat...

Hope that long winded explanation did it for you! [img]images/icons/grin.gif[/img]

[ December 10, 2002, 12:30 PM: Message edited by: Cleveland Metal ]

[StuTDavis]

Re: Help with tubes please!

Just a clarification on the biasing...you need to re-bias when you have different power amp tubes put in, NOT when you change preamp tubes. John did an awesome, long, informative post, but I didn't see this distinction.

Another funky thing to think about/consider... If you think you want more "power tube distortion", one thing you could look at are the THD Yellow Jackets. They're adapters that allow you to plug an EL84 power tube in the socket of an EL34/6L6 power tube in an amp. In theory, the EL84 should gain-up and distort quicker than an EL34/6L6 and give you more "power tube distortion", and a somewhat different character.

[Cleveland Metal]

Re: Help with tubes please!

Doh, I just edited the post to clarify that..

Thanx man! I was spewing so much gibberish, I missed that at first...

[OklaStrat]

Re: Help with tubes please!

Some of the JCM900s shipped with 6L6s or variants... I think mine had sovtek 5881s loaded in it. Pull a power tube (big ones) and just look on it. EL34s are generally long and skinny, 6L6s and 5881s are more squat and fatter.

Pete

[OklaStrat]

Re: Help with tubes please!

BTW, those amps are easy to bias - they already have a pot there. Mesa amps use the same biasing setup, but with no adjustment pot... as soon as my single recto goes out of warranty, it's getting modded... or maybe sooner. It's awful cold, even with my Tungsol 5881s in there.

Pete