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Author Topic: Marshall JCM 800 preamp tube type/combination  (Read 4595 times)

Nick Aghababian

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Marshall JCM 800 preamp tube type/combination
« on: February 04, 2011, 04:06:51 pm »

I spent an hour on google trying to find a suited answer and I couldn't. I figured there is enough knowledge on PSW to answer my question.

So finally, after almost 10 years of playing guitar (didn't realize it had been that long til just now) I upgraded from my Roland Micro-cube practice amp to a 50w MKII JCM 800 (NO mods). Before I had no reason to play at any other volume then bedroom level, but now it is time to start the collection and maybe start recording/playing out.

Currently there are 12ax7 pre-tubes (electro-harmonix I believe) and for my ears they are a little too bright and it's not something the treble or presence knob can fix. I like the gain, but I don't necessarily use all of it and if I sacrifice a little gain I'm ok with that. I have a set of new old-stock Amperex 12ax7's I could throw in if that might help.

I also have a set of RCA 12au7's and RCA 12at7's, but I don't know anything about the characteristics of these tubes. I read something about using different preamp tube combinations too.

Thoughts, comments and suggestions are appreciated.
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Bob Leonard

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #1 on: February 05, 2011, 02:11:46 am »

Nick,
Any 12AX7 can sound bright in any amplifier, however, Marshalls tone stack tends to add gain in the mid range and high end. Many people tend to confuse this piercing treble as chime. Glad to see that you haven't. Gain is not the reason for the extra treble response, although higher gain can and will accentuate the effect. What you need is a warmer tube in the pre amp stage of the amp.
 
I suggest that you try using a 5751 which has 80% of the gain of a 12AX7 and warmer response. The EH tubes are great tubes in Fenders, but stay away from Chinese tubes if at all possible as they are almost all too bright and piercing. I would also recommend trying a 12AT7 for the phase inverter. This will be the tube closest to the output tubes when looking at the back of the amplifier. Both these steps will tame the amp a bit and "warm" it up as well.
 
The output tubes could be the culprit also change those last if you still feel there is too much treble for your taste.
 
GT makes a great 5751 and would be a good source for the other tubes as well.
 
The last component to look at will be the speakers. I don't know what's in your amp now, but Celestion Vintage 30s seem to be the way to go, or Weber Blue Dogs, if smooth is the goal.
 
I don't know if Steve Hurt is lurking, but maybe he can compliment on the tubes I used when I rebuilt his amps. 
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Mike Reilly

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #2 on: February 09, 2011, 02:03:57 pm »

Nick,

Honestly, my first thought was if you've only spent an hour chasing tube info & opinions on the web, you've barely dipped your toe in the water.  ;D

Most of my tube-amp-tweaking was in the pre-internet days, but I found the Tube Amp Book by Aspen Pittman (founder of Groove Tubes) very helpful.  Note that currently a GoogleBooks search actually previews some of the pages (116-134) comparing different preamp & poweramp tubes.

The Groove Tubes website has some comparisons.  There's also guitaramplifierblueprinting.com which seems to be kind of an offshoot of the GT website.

Also vacuumtubes.com has comparisons.

Way back when (the 90's) Guitar Player magazine ran quite a few articles & columns about tube comparisons & swapping & amp tweaking. I don't know if any of those can be found on the web, but it's worth a look.

My own personal experience (again, roughly 15 years in the past) is that the interaction of tubes & amps & guitars & the player's ears tends to be . . . . highly individual.

Maybe it's just the specific tubes in your amp, and you could replace them with new EH tubes and be happy, maybe EH tubes in general are too bright and you would be happier with a different brand.  Some brands even separate tubes by country of manufacture, giving you even more options. Maybe (as Bob suggests) you could try a variation on the 12ax7.

My point being that while experimenting with tubes can be great fun, don't be too disappointed if your real-world experience doesn't match up with the info you find.  Lots of people will swear by NOS tubes, but you might hate that particular set of Ampegs in your amp with your guitar.

And like Bob points out, power tubes and speakers also play a big role in the sound of an amp.

HTH.

P.S.: I'm 99% sure any 12**7 tube can technically work as a plug-n-play replacement, but in practice, the 12au7 and 12ay7 are too low-gain - you could try a 12at7.

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Ned Ward

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #3 on: February 09, 2011, 09:40:42 pm »

Talk to Mike at kcanostubes.com. He's been my guy for over 12 years and tell him your tonal goals and your budget and he'll get you great glass, both new and NOS.
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Bob Leonard

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #4 on: February 10, 2011, 09:04:23 am »

Talk to Mike at kcanostubes.com. He's been my guy for over 12 years and tell him your tonal goals and your budget and he'll get you great glass, both new and NOS.

Hey Ned,
 
Not to swerve far from the OPs post but I was able to pick up a pair of Deluxe Reverbs last Saturday for $2200. One is an untouched 1965 and the other is a silver faced 1972 ($800).
 
The 1965 Deluxe ($1400) was blowing fuses so when I got it home I found an arcing 6V6, replaced it and the power supply caps. No problems now. The 72 is perfect, untouched and is AB763 to the last component. Never overlook those silver faced amps.
 
OP, the quickest and least costly way for you to experiment is to buy a pair of 5751s and put them into V1 and V2.
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Ned Ward

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #5 on: February 10, 2011, 09:28:16 pm »

Bob - very nice pick up! my princeton is a 73 and my PR a '77, but they still sound very sweet indeed.


Haven't been able to spend on the guitar amps lately; although was tempted spending a half hour at Truetone music, where they left me alone in their Dr. Z amp room with a 56 goldtop reissue...


Hopefully the taxman will giveth some back.


Agree a pair of 5751s would be a good start for the preamp tubes.
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Steve Hurt

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #6 on: February 19, 2011, 11:03:19 pm »

I don't know if Steve Hurt is lurking, but maybe he can compliment on the tubes I used when I rebuilt his amps.


I don't know if it's the tubes or the wires or the elbow grease or the eletcro-thing-a-ma-bobs, but I will say that
Bob did a hell of a job on my 2 amps.

I had a local guy with a national rep do one of them and Bob had to tear it all out and do it over to make things right.
The other one was a total rear down and rebuild. 

Both amps are significantly better than anything I've heard available new.  Bob knows what he's doing with tube amps!

Now if he's just put down those Gibsons and get a Telecaster!.............
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Walter W Wright

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #7 on: February 20, 2011, 10:56:34 pm »

+1 on bob's suggestion of the 5751s. they'll take some edge off (along with some gain). i ultimately took 'em back out of my old marshall, but they were an interesting variation.

i'd be wary of ATs and AUs, those aren't really the same kinds of tubes.

gotta argue about the vintage 30s, though. those are bright, loud-ass guitar speakers, especially with naturally sizzly master volume marshalls. the best thing i ever did with my '78 2203 (an older, 100-watt version of the same amp) was ditch the V30s in my 2x12 cab in favor of a pair of the celestion heritage G12-65s. these are noticeably darker and quieter (less efficient at like 97dB vs. 100dB for the V30s), having a smooth, creamy tone that lets me turn the amp itself up for more sonic goodness without getting my band fired from the club. they made way more difference than the preamp tubes.

it's like the G12-65s were made for those amps.
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Bob Leonard

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #8 on: February 28, 2011, 07:06:00 am »


I don't know if it's the tubes or the wires or the elbow grease or the eletcro-thing-a-ma-bobs, but I will say that
Bob did a hell of a job on my 2 amps.

I had a local guy with a national rep do one of them and Bob had to tear it all out and do it over to make things right.
The other one was a total rear down and rebuild. 

Both amps are significantly better than anything I've heard available new.  Bob knows what he's doing with tube amps!

Now if he's just put down those Gibsons and get a Telecaster!.............

You're very kind Steve, thank you. The offer to increase Headly Lamar still stands FOC except shipping. Oh, and the Gibsons stay.
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Jeff Bankston

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Re: Marshall JCM 800 preamp tube type/combination
« Reply #9 on: March 09, 2014, 07:34:56 am »

old thread. i have a pare of jcm800 2205 amps. i like the EH(Electro Harmonix) EL34 and the EH 12ax7 in 4 places. mine are 1988 and 1989 and V2 is only active in the clean channel. 1981-1983 2205 and 2210 amps are hardwired and is the first circut design. there were problems with channel bleed and the 1984-1986 amps circut were redesigned and no longer hard wired. there was still channel bleed problems and in 1987 the circut was redesigned again and stayed the same from 1987-1990. all 3 circut designs have their own sound. from what i'v learned tubes will sound different in different designs. the 1981-1983 V2 tube is also active in the distortion channel. a foto of my "Double Trouble" stack. can you say keyboard amps ? i use the celestion g12t-75 speakers. maybe your laying sideways and are a foreinger with double vision.
« Last Edit: March 09, 2014, 08:57:46 am by Jeff Harrell »
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