opinions on preamp tube experiment on Mark IIb ?

[gonzo]

i have a '81 60 watt graphic eq mesa boogie mark IIb, that i've only ever put the standard boogie tubes in..

i'm curious to experiment with some different brands and strengths...

i'm now using the head to record with, and to that end, i've added a Weber Mass Lite (100W) attenuator, and am pulling a direct feed to the recorder via a Palmer PDI-09 Junction box, which is fed BEFORE the weber.

the palmer captures the full output, and then the WEBER attenuates the volume for monitoring (i sometimes mic the cab, and blend it with the palmer).


so, i'm running the master volume on 5.
the lead master, on 6.

anything higher, only gives me compression, which is not what i'm really after.

what i'm finding is that because of the power amp saturation and distortion, i'm having to run the Vol 1 much lower than usual (about 5-6 on Vol 1) to get a clean-ish tone on the rhythm channel.

i was thinking that maybe a cleaner V1 (maybe a 12ay7 ?) might be worth the experiment.

also, i guess, while i'm at it, which POWER TUBE SET would give me the least amount of compression at saturation?

i feel like such a noob....

 

[ANIMATED SUSPENSION]

Which type of M/B tubes are in it ? I'd try STR440's in code white and back off the guitar's volume a bit. If the pre amp tubes are Russian 1's or 2's and are pretty new, they should be fine. Using lower gain pre amp tubes doesn't sound like it would help your problem.

 

[stokes]

A good NOS 5751 will get you in the direction you are looking for,the 12AY7 will be too low gain.But dont use the current production 5751's,to me they sound like cheap 12AX7's,brittle,harsh and weak.

 

[Tubegear Junkie]

A good NOS 5751 will get you in the direction you are looking for,the 12AY7 will be too low gain.But dont use the current production 5751's,to me they sound like cheap 12AX7's,brittle,harsh and weak.

agreed!!

General Electric made a special 12AX7 with slightly
less gain called a 5751.
I believe this is the one that stokes is referring to.

 

[Rocky]

The 5751 is not exclusive to GE. Many companies made 5751s

A 5751 has about 30% less gain than a 12AX7A/ECC83/7025

 

[Tubegear Junkie]

The 5751 is not exclusive to GE. Many companies made 5751s

A 5751 has about 30% less gain than a 12AX7A/ECC83/7025

I didn't say this, "exclusive"- stop putting words in my mouth.
What's up with the constant harassment from you- your acting like a immature little kid- maybe you are.

 

[Rocky]

Not harassing you at all, just pointing out that the 5751 wasnt a GE invention...rather the 5751 is just a variant on the 12AX7.

 

[gonzo]

OK GUYS...
the current tube sets are:

preamp:
mesa 7625 str
12ax7-A ecc83

power:
6L6 GC
STR-420


these have typically been the tubes sets i've always used..
now, the sets that are in there now, are well within spec for each tube tested...

so, i guess i'm simply looking for a different flavor, and with lots more clean headroom, because i'm driving the output into serious saturation, but what i want is less compression, and more harmonics.

??????
i'm clueless here..
and appreciate all opinions and suggestions.

 

[stokes]

"so, i guess i'm simply looking for a different flavor, and with lots more clean headroom, because i'm driving the output into serious saturation, but what i want is less compression, and more harmonics."

If the power tubes are stock biased Mesa tubes,I seriously doubt you are anywhere near "driving the output into serious saturation".Mesa sets the bias way too cold to get near saturation,all the overdrive you hear is from the preamp.Try a NOS 5751,GE or RCA or whatever you can get your hands on,as long as it isnt the current production Russian 5751.

 

[ANIMATED SUSPENSION]

Changing pre amp tubes isn't really going to help the power amp saturation. The problem is the STR420's, they're renowned for their early distortion, I say again, get some STR440's code white or blue, they'll give you the max headroom and still be in spec for the amp.

 

[gonzo]

ok great!

got some ideas to try out....

now, i can guarantee, the power amp is seeing saturation, either that, or the transformer is weak from age...
i haven't had it tested, tho the entire amp was given a checkup about 7months ago, and is entirely in spec now.....

but the idea of the 5751 on the pre side, and the STR440's sounds like a plan!~

i like the feeling the amp has, when everything is about at it's optimum setting....
where the power amp side pretty much hits the ceiling, and then i back it down a touch from there...

so, it' makes sense that i'd want cleaner preamp tubes too-- if what i'm really looking for is happening more on the power out side..

if i wasn't using the attenuator, i wouldn't even be changing anything....
but this is a great experiment!