Switching to lower power tubes?

:?:

Anyone tried this much(see below)..Like, dislike.... experiences......?

A word about the 12AXTUY7:

If a12AX7 tubes has "100% gain" then the 12AT7 has 40% less output, or put another way 60% gain. The output is further reduced another 20% with the 12AU7 with 40% gain. Finally, with the 12AY7 a further 20% output reduction is achieved to have a 20% gain. With this in mind, some suggest that using a lower gain tube in V4 gives the reverb a better tone. As well, one can put a 12AT7 in V3 and soften the overall gain of your amp. Check it out, no harm can come to the amp and one can soften the gain quite a bit.

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They're not really lower power, just lower gain. Means the sound is cleaner, not lower in volume. If you run the gain/overdrive/distortion on your amp at 6 with a 12AX7, you'll need to crank it up to 10 with a 12 AT7 in order to get about the same level of dirt. You need to look at the tube tasking chart or a schematic to figure out which tube does what - not all amps use the same tube positions (V1, V2, etc.) for the same tasks.

I just looked at the Mark II Maintenance & Repair docs that came with the amp. They do show position V2 can use;

1. 12AT7 for cleaner sound

2. 12AX7 for distortion

What about when you put the EL34's in 1st and 4th positions for the output side. And then just play those tubes...will it sound kinda like a Marshall amp? I forget what I've heard that sound called..Brown sound or something like that....

RocketRick said:

What about when you put the EL34's in 1st and 4th positions for the output side. And then just play those tubes...will it sound kinda like a Marshall amp? I forget what I've heard that sound called..Brown sound or something like that....

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Don't know what amp you have. A Mark II? Simul-Class?

Mark IIc+..Has EQ and the export input Voltage switch. According to Mike the best one made and with the 105 Pwr trannie. Mike did the burn in so to speak.



Does that help?

RocketRick said:

I just looked at the Mark II Maintenance & Repair docs that came with the amp. They do show position V2 can use;

1. 12AT7 for cleaner sound

2. 12AX7 for distortion

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Is that document titled "Mesa Boogie Mark II-B Maintainence & Repair"? I have the same document that came with my IIC. However, the Mark II-C Maintainence & Repair document (PDF availalbe at Mesa's site for download) calls for 12AX7 for all five preamp tube sockets.

"If a12AX7 tubes has "100% gain" then the 12AT7 has 40% less output, or put another way 60% gain. The output is further reduced another 20% with the 12AU7 with 40% gain. Finally, with the 12AY7 a further 20% output reduction is achieved to have a 20% gain."

by this math, if i have 3 12AT7's in v1-v3, i'll have -20% gain. that's pretty low output. maybe if i use some low output pickups and roll my guitar's volume knob down, i can get to -100% gain. that would be pretty awesome amirite?

Looks like MMIII has a clue at least...

I have the same amp: loaded Simul C+ with export trans. I would highly recommend a 5751 in V1, particularly a black plate, triple-mica RCA (the triple-mica really keeps it quiet). The 5751 is a lower gain 12AX7, and for me it smoothed out some the C+ growl in a very good way. I've also had great luck with a new Mullard 12AT7WA (CV4024, balanced triodes) in V5 (phase inverter). This also helped smooth out the sound. I like it so much in V5 that I didn't even try it in other slots! I've also tried vintage AT7s and AU7s in assorted slots, but I wasn't very impressed with the results. For me, I don't think I'll ever run the C+ without the RCA 5751 in V1.

It also depends on the sound you're after. I'm not a high gain player, but more of a Keith Richards style rock'n'roller. I play almost exclusively on the lead channel, as I prefer an aggressive, barking, articulate rhythm sound with both a Strat and Les Paul - the "Fender on steroids" sound. I use pickup selection and guitar controls when switching between rhythm and leads. It's easier on the LP as the pickups have independent volume controls...more of a challenge with the Strat. It depends on what sound you're after.

dodger,

Thanks for that. I'll def try those tubes. If they tame it down some especially with the hum etc it'll be an improvement.

1st will try the El34's in outside positions.

Well I want to do reg Rock, R&R and some jazz stuff a little. I too have an awesume Strat and Studio LP, 2 Studio DC's(P-90's) and Tele Lead II + '54 Jr and and '54+/- ES140T 3/4.

I have two Marshall heads, JCM 800 and DSL 2000, and it will be nice to see how the tube changes of the Marks II sounds compared to the Marshalls.

RR
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ev1ltwin said:

"If a12AX7 tubes has "100% gain" then the 12AT7 has 40% less output, or put another way 60% gain. The output is further reduced another 20% with the 12AU7 with 40% gain. Finally, with the 12AY7 a further 20% output reduction is achieved to have a 20% gain."

by this math, if i have 3 12AT7's in v1-v3, i'll have -20% gain. that's pretty low output. maybe if i use some low output pickups and roll my guitar's volume knob down, i can get to -100% gain. that would be pretty awesome amirite?

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Low gain does not equal low output. If you replace all the tubes with the highest gain possible, all that's needed to reduce the output to zero is to turn the Master down to zero. Anyway,the power tubes determine output, because they're in the, uh, output section.
Hope this helps.

RocketRick said:

dodger,

Thanks for that. I'll def try those tubes. If they tame it down some especially with the hum etc it'll be an improvement.

1st will try the El34's in outside positions.

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If I'm not mistaken, there is a minor mod that needs to be done in order to SAFELY run EL34's in the outside sockets. PM Boogiebabies; he'll know for sure.

dodger916 said:

RocketRick said:

dodger,

Thanks for that. I'll def try those tubes. If they tame it down some especially with the hum etc it'll be an improvement.

1st will try the El34's in outside positions.

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If I'm not mistaken, there is a minor mod that needs to be done in order to SAFELY run EL34's in the outside sockets. PM Boogiebabies; he'll know for sure.

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Yes, pin 1 and 8 need to be connected.

gts said:

I understand the pin 1 and 8 being connected mod but you can use El34's in the two outside sockets of a Simul-Class amp without the mod. Mesa designed Simul-Class amps to use El34's in these slots. If I'm not mistaken the mod adds a level of safety.
I think Joey B had an issue with El34's in one of his Simul C+'s. But I have used El34's in the outside sockets of mine with no issues to date.

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You're right, they were designed to do so. I talked to Mike B about this a few months ago. He basically put it as EL34s were much higher quality back then and the mod wasn't necessary to protect the tube but now they recommend the mod because of the quality of new stock tubes. Mike said he recommends having it done if you use EL34s in the outer sockets.

All,

Mike said that my amp, and he tested it and signed off on it, can use some of the older Sylvania or GE tubes, that have pins 1 & 8 connected, in positions V1 & V4 w/o the mod. Other wise, you need to do the mod.

From talking to him, it sounded like the mod was not done on their amps unless sent back for service. Whether it was done automatically I don't know.

Really neat to be able to talk to other owners of the amp and share info.

Thanks Everyone and rock on!!..

I emailed Myles at the "Musciplayers" forum about the mod. He said;

I would not use EL34's in the amp for two reasons .... the output transformer is not a match for EL34s and the screen resistors may not be 1K ohm 5 watt resistors as would be best used.

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and

If the screen resistors are 5 watters rather than 470 ohm 3 watters then I'd go ahead and try it.... if you like it then thats all that matters.

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rick

RocketRick said:

I emailed Myles at the "Musciplayers" forum about the mod. He said;

I would not use EL34's in the amp for two reasons .... the output transformer is not a match for EL34s and the screen resistors may not be 1K ohm 5 watt resistors as would be best used.

Click to expand...

and

If the screen resistors are 5 watters rather than 470 ohm 3 watters then I'd go ahead and try it.... if you like it then thats all that matters.

Click to expand...

rick

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I do not doubt that this guy is giving you sound advice for the EL-34's. But would this setup be optimal if you wanted to switch back to 6L6's? The Simulclass C+ was initially designed for all 6L6's , and later allowed a substitution of the 6CA7 in the outer sockets. Hence, the not so optimal transformer for the EL-34 type tubes.

FWIW, you have spoken to Mike Bendinelli about this issue, correct? He and Randall Smith are the highest authority on the design of the MkIIC+, in my opinion. Neither of them would steer you wrong. 8)

AAMOF, I talked to Mike today and he confirmed what you guys said. That lots of the amp thru the years have done it w/o problems.

So I'm on board so to speak.

I was just wanting to get another opinion.

So Joey, are you NOW using that config?

Rick

As we speak, both of my C+ amps are running a Sylvania STR-415/416 combination without any issues whatsoever. They both have the 1-8 pin mod, wheather they need it or not. 8)