12AT7/12ATY7 in a JCM800?

[DrNewcenstein]

Probably been asked a billion times already, but anyone put 12AT/AY7s in a JCM800 to get a bit more useable Cleans from it?

I know, crazy, right?

But I'm finding myself gravitating more towards relying on pedals for all the dirt, rather than just boosting what's already there, and I may as well just run into the Return in that case.

So, what value preamp tubes would I need to get cleans up to about 3-5 on the Gain knob, but still be able to push it up to 10 with a pedal to get the "classic Marshall sound"? I mean, if I could tone it down to where Gain on 10 = Gain on 5 now, that'd be nice.

Right now the Gain is on like 2, maybe, and if I get too heavy-handed it breaks up, which I'm not after.


I know, I know, "just get rid of the Marshall, thou unworthy and blaspheming heretic!" but there it is.

Then again, I guess with the M13 I could maybe rig it up so it goes into the front and the loop - dirt pedals go through the Input, but when I switch to the clean crap I go into the Return. Hmmm.

Thoughts?

 

[zzmoore]

Re: 12AT7/12ATY7 in a JCM800?

Its one of those questions that is almost not worth asking.
There are only a few choices, the new tubes (and some of the NOS) are not expensive, just try it. Nobody knows what you will prefer.
The AY will drop the gain "A Lot".....but maybe that is what You want. Also try a 5751.
good luck

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

Thanks. It's a starting point, anyway. And yeah, dropping the Gain is what I'm after, unless, as I said, I can rig something up so that dirt/boost pedals go in the front but when I go to the clean stuff it switches to the power section, bypassing the preamp.

 

[vinta9e]

Re: 12AT7/12ATY7 in a JCM800?

Ultimately I realized that the 80s Marshall sound I had in my head for years does not come from any factory stock amplifier. Incidentally, the right mod delivered unrivaled clean up, too.

 

[TwilightOdyssey]

Re: 12AT7/12ATY7 in a JCM800?

Another valve I would recommend trying is the ECC832.
If your amp uses both sides if the triode, the first half of the ECC832 is an ECC83 and the second half is an ECC82.

I have found that it retains the sound, feel, and response of an amp designed for the ECC83 but drops the gain WAY down. It also retains the sponginess of the ECC83; one of the things I don't like about the 5751 is how stiff it is.

You can still wind up the gain as well, and it takes drive pedals REALLY well.

Out of curiosity, what is the sound you are after? What guitar/cab are you using?

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

No specific sound in mind - not like "I want JC120" or "Twin" tone, as there are differences in the circuits, but something as clean as those get. I haven't checked out 2-channel Marshalls, so I'm not familiar with the clean tones they can get, but basically what I'm getting now with the Gain on 2 and the Master on about 8 or 9, but with the Gain and Master on about 5 each. That way I've got room on the knob to go higher if I need it for some reason.

Cab is a Carvin 2x12 with their British 12s. 300w power rating.

Guitar in use is a wide range of humbuckered Jacksons. Mostly Floyded Alder and Basswood bodies, a few mahogany w/maple cap, with an equally-wide range of Duncans: Distortion, JB, Customs (A2, A5, and Ceramic versions), Invader, PATB 1 and 2, Alt 8, 59B/N, JazzN, as well as "the big 3" EMGs (81, 85, 89).

I know you need at least some amp dirt for a boost pedal to work with, but tweaking the Gain knob up to 10 while I kick on a Tube Driver and then back down when I'm done isn't really something I want to get involved with.

Maybe if I take it in steps and inch the gain saturation down one tube at a time I can find a happy medium.
I certainly don't want to castrate the amp, I just want to scale back the built-in dirt.

 

[zzmoore]

Re: 12AT7/12ATY7 in a JCM800?

from reading your above post, I would say start with an AT7 in the PI.

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

Cool. I think I actually have one on-hand.

 

[dystrust]

Re: 12AT7/12ATY7 in a JCM800?

Good luck with your tone quest; I really hope your attempt works out better than mine. I spent a few weeks tube rolling with my bro's '78 JMP 2203 and I was never able to find the balance you're looking for. The stock 12AX7s had too much gain to really be able to play clean with the guitar volume rolled up. Switching to 12AT7s dropped the gain too far; overall volume dropped off and the amp would barely break up even with the gain dimed. I didn't have access to 5751s or ECC832s, so those might work better.

I ended up trying a Mesa Studio Preamp and an ADA MP-1 into the low input as well as running the amp completely clean and using various dirt pedals. Finally I just gave up, put the 12AX7s back, and used a different amp for those other sounds.

 

[El Supremo]

Re: 12AT7/12ATY7 in a JCM800?

Lots of folk recommend a 5751 in the V1 position from what I've been reading. Haven't tried it myself with the JMP 2104, but that would be my first shot.

 

[Gearjoneser]

Re: 12AT7/12ATY7 in a JCM800?

One nice thing about the JCM800 is it's second input makes the amp entirely different. It turns it into a big bassman tone where your master and gain can be turned way up. Then, it's a big fat clean tone perfect for using gain pedals. I've heard people say 800's don't sound like plexi's, but they may have never used the second input with the volume high before.

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

True, there is the 2nd input with reduced gain. Actually forgot about that and it's 3 feet away from me. Derp.

 

[dystrust]

Re: 12AT7/12ATY7 in a JCM800?

One nice thing about the JCM800 is it's second input makes the amp entirely different. It turns it into a big bassman tone where your master and gain can be turned way up. Then, it's a big fat clean tone perfect for using gain pedals. I've heard people say 800's don't sound like plexi's, but they may have never used the second input with the volume high before.

True, there is the 2nd input with reduced gain. Actually forgot about that and it's 3 feet away from me. Derp.

I wouldn't say the 'low' input sounds like a plexi, but it's definitely a different amp. I definitely agree w/ the Bassman vibe, but the feel seemed a lot more stiff than a Bassman or non-master Marshall. Maybe the difference is in the power supply or power section damping?

I didn't recommend using the low input in my earlier post because I was under the impression that DrNewcenstein wanted some overdrive to still be available. With my bro's JMP I could hardly get any breakup from the low input even with the gain cranked and 12AX7s in the preamp. If you're OK with using an external preamp (like an ADA-MP-1) or a distortion pedal, the low input works great for that.

 

[Gearjoneser]

Re: 12AT7/12ATY7 in a JCM800?

The other day, I used my JCM800 head and combo's 2nd inputs with all my Bogner pedals, and it was shockingly good. It made me realize that I can use JCM800's with boost pedals into their #1 inputs for tight highgain, or dirt pedals into their #2 inputs for huge fat gain. The more I play with 800's, the more I dig them. They are one of the best platforms for pedals, and depending on your tubes and speakers, you can always get a JCM800 situated to sound perfect to you.
Their status as classic amps isn't without merit. I'm talking 6 knob versions. The channel switching ones were good, but the single channel ones really have a great tone, once you get it all dialed in.

 

[TwilightOdyssey]

Re: 12AT7/12ATY7 in a JCM800?

The other day, I used my JCM800 head and combo's 2nd inputs with all my Bogner pedals, and it was shockingly good. It made me realize that I can use JCM800's with boost pedals into their #1 inputs for tight highgain, or dirt pedals into their #2 inputs for huge fat gain. The more I play with 800's, the more I dig them. They are one of the best platforms for pedals, and depending on your tubes and speakers, you can always get a JCM800 situated to sound perfect to you.
Their status as classic amps isn't without merit. I'm talking 6 knob versions. The channel switching ones were good, but the single channel ones really have a great tone, once you get it all dialed in.

I totally agree with this line of reasoning!

GJ, if you ever have the chance, I strongly recommend grabbing an NOS (or even OS, as legit NOS are getting virtually impossible to find) Telefunken 803S or Siemens ECC83 for the V1 slot in the JCM800...

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

Going through my tube box, I've got:

Magnavox:
-USA:
--6CY5 with the numbers 31, 33, and 79 next to EC
--6EU7
--12AT7
--5U4GB

-Japan:
--6BA6
--6BE6
--6BQ5

-Great Britain:
--6EU7 with the number 1022-206

RCA 6EA8 (USA)

and one USA-made without a logo 6AL5

I've also got some 12BZ7s (I believe?) somewhere that I got off Ebay a couple of years ago. They're an extra-long 12AX7.

 

[Gearjoneser]

Re: 12AT7/12ATY7 in a JCM800?

I'm not sure using tubes to knock down the gain level will get you what you're looking for.

Have you tried plugging into the #2 input, turning the gain and master to 6, and using drive pedals?

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

See post #12 :lol:

I tried both inputs when I first got the M13, but IIRC I didn't really want the pedals doing all the work - may as well just run into a poweramp if I'm going to do that.

But then I'm schizo with C.R.S., so I'm often undecided on some things and forget what those things are :lol:

 

[JeffB]

Re: 12AT7/12ATY7 in a JCM800?

The problem I have found with tryng low gain tubes in v1 is that they always thin the amp out, while also reducing gain.

I have not tried the 832 though.

That said, I think you might be trying to turn an apple into an orange..The whole MV/2203 was designed around the need for more gain. The great clean tones they get, like, e.g. Andy Summers, are done with low output bright pickups and low volume levels

 

[DrNewcenstein]

Re: 12AT7/12ATY7 in a JCM800?

I haven't tried it yet, but suppose I ran an A/B pedal with A going to the High Gain input and B going to the Low Gain input? Or if the M13 can do its own internal switcheroo so I can route cleans out of one Output into the Low Gain input and Dirt to the High Gain input?

Or is the amp set up so you can only run either/or, and it defaults to one or the other if both inputs are occupied?

Worse, would it break something if I ran into both at once?