#1
So I recently got my Marshall JCM 800 back from the repair shop. It's good to have it back

However, I find myself in a new dillema. I know it's an older amp, but I'm trying to get a heavier tone out of it. I'm not expecting any death metal tones out of it, but I am trying to get something like old Metallica, or maybe a "Hatebreeder" Childern of Bodom tone. Even with the volume on the overdrive channel cranked, and a bad monkey overdrive in front of it with the level cranked, and the gain about half way up, I still can't quite get those power tubes to break up enough! Granted, I AM using 6550 output tubes, but have wondered if switching to EL34's would do the trick? Help would be appreciated!
- Gibson Flying V 120 #1 (White)
- Gibson Flying V 120 #2 (Cherry)
- Gibson SG Standard ('61 style)
- Jackson DK2M

- ENGL Fireball 60
- Avatar 4x12

- Many pedals, plus other stuff
#2
You'll never be able to get a bare bones JCM 800 to deliver enough gain and saturation to sound like COB or metallica, reguardless of what power tubes. Its just not that style of amp.

I recommend a different head altogether, but a great pedal to use infront of a JCM 800 for Over the top distortion is the Damage Control Liquid Metal pedal. Its a 2 12ax7 pre amp that has gain for miles. Very thick and punchy distortion. Run that infront of the marshall and you'll be where you want to tone wise.
#3
i run EL34's in mine, the gain is Nice But for my desire to have harder sounds I blend it with a mesa dual rectifier running EL34s.. I did notice a nice gain sound when upgrading to svetlana tubes which is who makes mesa boogies tubes. Id stay away from the Sovtek/ Electro harmonix tubes, I bought 12AX7's and EL34's from Sovtek/EHX and they made the amp buzz and produce terrible shrill sound.. I did a proper tube burn in- tapped them, ran them hot, ran them long and the russian tubes aint cuttin it for me anymore, I ruled them out of my life for good....

Your not running single coils are you? I've had a few fender guys say that jcm800s are weak, they are wrong, strats are weak output, heh. Humbuckers sold seperately I suppose
#4
I've managed to get somewhere closer to what I want tone wise Not exactly COB or Metallica, but still, something with more balls than before. It does rely on the OD pedal and the volume knob of course though

I'm running humbuckers of course, haha. I'm using a 500T bridge pickup in my Gibson Explorer, and a Seymour Duncan JB in my Jackson DK2M.

As far as what tubes I'm running goes, I have Groove Tube 12AX7's in the pre-amp, and Valve-art 6550's in the power amp. I've thought about going back to EL34's for more breakup at high volumes, but I love the low-end from the 6550's, and fear going back to EL34's would make it impossible to get a decent clean tone. It's been almost 2 years since the amp was retubed though. Maybe it's due for some new tubes soon?
- Gibson Flying V 120 #1 (White)
- Gibson Flying V 120 #2 (Cherry)
- Gibson SG Standard ('61 style)
- Jackson DK2M

- ENGL Fireball 60
- Avatar 4x12

- Many pedals, plus other stuff
#5
is it a single or dual channel 800. the single channel JCM800's have less built in gain and are more liek 60's and 70's Marshall's while the dual channel 800's have more gain and bite. I'm suprised you need more gain. Remember those amps had a lot of gain in their day. By today's standards they are medium gained amps. I use a single channel 800 with a tubescreamer and it's all the gain I'll ever need.

I think a change of tubes might help. Try EL34's and adjust the bias so it's pretty hot (about 85% dissipation), And buy high gain pre-amp tubes.

If you still need more gain, you might want to look into a more modern high gain amp
#6
Ya, the 6550's take longer to break up than EL34's and especially EL84's which are notorious for breaking up at lower volumes.

Another thing to do is see if you can have a 1/2 power switch moded to it. I ALWAYS play with my JCM 800 at only 25w, and can crank the volume knob pretty high even in my bedroom. Another thing to do is get a good overdrive. Metallica's exact gear on Ride The Lightning was Humbucker-->Tubescreamer-->JCM 800. That's exactly the gear that I have and I get the RTL tone perfectly (hence my username), even with a Strat!
My Gear:

Guitars:
Fender American HSS Stratocaster

Amps & Effects:
Hand-Wired JCM 800 2204
Hand-Wired V30 2x12 Cab
Keeley TS-9 Tube Screamer
ISP Decimator
EHX Holiest Grail
Modded Dunlop Crybaby
Boss RC-2 Loop Station
#7
If it's a single-channel 800, you could try a Soldano Hot Mod. Works just like those Yellow Jackets, from THD.
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#8
It's a dual channel JCM 800 . The first year of the dual channel ones actually! (1982)

The thing actually has a butt-load of pre-amp gain. The problem is that it's not very usable. If I turn it up past 6 or so (1 o'clock), it starts to sound "overloaded" and harsh. What I do right now is leave the gain up around 5 or 6, then use my OD pedal in front of the amp for a boost. At high volumes, it's enough gain for early 80's metal rhythm, but a bit more sustain would be nice for lead. And pinch harmonics of course

I dunno if it's the tubes or what. I could've sworn one was going microphonic on me not too long ago too though. I think I had the gain up around 7 or so, cranked the volume, and it squealed like a pig.

Maybe some new pre-amp tubes and EL34's would be my best bet?
- Gibson Flying V 120 #1 (White)
- Gibson Flying V 120 #2 (Cherry)
- Gibson SG Standard ('61 style)
- Jackson DK2M

- ENGL Fireball 60
- Avatar 4x12

- Many pedals, plus other stuff
#9
you should definitely be able to turn the pre-amp up past 6. I would get a whole new set of tubes and go from their.