software

Here's my delima. I have my Jeff Seal modded JCM, which I love. It's got a slight hiss on both the clean and OD channel, which I attribute to the power tubes.....it's time to have them replaced. The old version of my amp was so harsh that I went to great lengths to smooth it out and get rid of the harsh, that I think I may have gone too far. However, there is more.

I have been playing my Boss GT-6 primarily as of late, because I can use my wireless headphones with it and not disturbe the family. What I have noticed is that now when I plug into the Marshall, the quot;crunchquot; is not as tight as I remember. Part of this is due to not having played the Marshall in a while, and having my ear used to the GT-6. I've talked to Jeff, and the circuit is not the issue. He suggested trying the GT12-75's again, as those are the speakers it was voiced towards....I'm putting those back in tonight.

Here's what I am running tube wise now.

V1 - NOS RFT
V2 - NOS RCA Blackplate
V3 - NOS Bugle Boy
V4 - JJ
PI - Balanced JJ

Power - Svetlana Winged C's

What tubes do you all think will make the difference? My original plan was to order some NOS Siemens (that are very close to old Mullards) for power, and to go with GT 12AX7-M's for at least V1 and V2, but now I wonder if that would be too smooth again. I don't want grit or harsness, just better crunch, while still remaining smoothness. I'd also like a tad more gain from the amp. I'm going with a Carl Martin Plexi boost soon, but want the majority of the crunch to come from the amp.

GT 12AX7-C's?
GT6CA7's for power?

Give me some suggestions. Remember, not harsh, not gritty, not overly sharp like 5881's or 6550's...I like the EL34 sound, but want a little more bite and clarity.

Anyone.....Bueler?

I think some of the hiss might be from a NOS preamp, just because they're not new enough.?? I'd buy GT 12AX7C's for all the tubes except the PI. I've found that the C's have the tightest sound in highgain amps. The M's are best for non mastervolume type amps. The power tubes are probably perfectly fine, although it wouldn't be a bad idea to check the bias on it.

Opinions may differ on bias, but to me it's easy, I just pull the chassis out, and carefully adjust the mini pot till the amp sounds it's best. I wouldn't recommend that to anyone who has no electronic experience, but hand biasing by ear will get the amp sounding exactly how you like it, and most likely it'll be pretty close to what it would read on a scope. It's best to do this with a cheap bias probe hooked up between a power tube and the socket, just so you know the mA's are around 35-39mA

It would probably help if I knew where the mini bias pot was. I'll give the GT-C's a try....I figured that's what you'de recommend GJ. If I do need to replace the power tubes, do you think those GT 6CA7's are good, or will they have too much of a 6550 vibe? I don't want to lose the midrange squish of the EL 34's, just tighten up the crunch a bit.

Also consider:

Sovtek 12AX7LPS
JJ E34L's

i find the chinese 12ax7 to be a very warm tube, jj ecc83 has a little more crunch to it, gt sells it as a gtecc83s.

I really like the Sovtek 12AX7LPS and the Sovtek WXT EL34's. I also use EH el34's and love them also. I think the EH's have more of a bite and a tad more brightness with a bit more clarity. The JJ's are good but, I think they are more along the lines of the Sovtek LPS's if I remember correctly.

I would recomend EH's for what you want.

If it's hiss, it's most likely the preamp tubes. Power tubes just get dull sounding over time. Pre tubes display all kinds of symptoms. 1 on the Sovtek LPS Those, and the Chinese pre's always sound really good in highgain Marshalls.

Jeff, I would never use the tubes you're using in a high gain situation, but that's just my opinion. I'm not a tube roller, but I am a high gain player.

For preamp tubes, I would look into Chinese GTs if you want more grit. They're cheap enough to experiment with and can always serve as emergency backups. I use Siemens fer my Marshall, tho. Not too soft at all.

I would go with Elctroharmonix before Sovteks; mostly because all of the Sovteks I've used sound like muddy, indistinct crapola.

Thanks guys....I think there may be more to the situation. I'll start a new thread to explain.

You grabbed my attention with your current tube line-up..............I'm curious, what did Jeff Seal put in there when he modded it or did that not include tubes?

I put RFTs in my Splawn amp; IMO they make the JJs sound silly...amp; I've got the Mullard EL34s........but I'm not really a high gain kinda' guy; more '70s style rock.

In playing around with tubes when I had the UniValve, I thought the Sovteks were definitely the grittiest while still sounding good. And GJ turned me onto the Chinese 12AX7s...they were pretty good too.


Originally Posted by PUCKBOY99You grabbed my attention with your current tube line-up..............I'm curious, what did Jeff Seal put in there when he modded it or did that not include tubes?

When Jeff modded it, I sent him the tube lineup that I was using at the time. It was a series of tubes that Mike @ KCANOSTUBES suggested to me.

V1 - RFT
V2 - NOS GE White Lable
V3 - EH 12AX7
V4 - EH 12AX7
PI - JJ - Balanced

I don't believe that Jeff voiced the amp to those partictular tubes. I've done plenty of tube swapping in this amp, and have only recently had issues with hiss.

FWIW, I like the RFT better than any tube I've tried so far (in V1 for gain)...including a NOS Bugle Boy and a NOS Mullard. I'm going to try some of the GT12AX7-C's, and some of the M's, to see if I like them, once I get this hiss thing figured out.