Mesa Boogie Peeps

[Casper]

Hi Folks-
Getting ready to do some amp stuff for end of the year as we have some down time in January. For Mesa owners..what are you guys using for
V6/Phase inverters tube wise 12 AX7 or 12 AT7..?
Does it REALLY make a difference? I'm changing my power tubes (6v6/EL84s) and I ordered a TungSol Balanced 12AX7 for the PI. After reading some various blogs, it seems I should have gone with the 12At7 instead. I have an AT7 in there now and it is fine..(I couldn't rmemeber at the time I ordered the tubes)
Any opinions or experience here?
Shaun

[picnic]

I stick with the stock MB tubes in my LSS. I tried JJ's but found the MB tubes nad a sweeter sound

[MojoRojo]

I ran tung-sol 12ax7's in my Mark II's with JJ power tubes. Used ax's and no at's.

[Casper]

Question: Do preamp tubes have "tone" already or pre-designed for tone OR is it their power or plate voltage in a certain valve position that determine what tone the amp will have? (12AX7 vs. 12AT7 or etc..)

If they DO have tone, how do I determine which tube or manufct, has more or less bass/mids/treble?
Thoughts?

[tom]

That's a pretty simple question with a very complex answer. I won't begin to say I understand the "why" of different tones but it is a complicated relationship between many components.
The different letters assigned to preamp tubes describe gain but tone and gain are again related. Tube brands also sound different.
Tube Depot does a pretty good job of describing different brands but I'm sure there are lots of other sources.

[Casper]

Thanks Tom! I have an understanding of the letters and what each preamp gain range is,..but what I've learned so far is that a 12AT7 has 10 to 15 times more plate voltage BUT has 30% less gain than a 12AX7. For tone's sake, my question still stands... Example: Does a Mesa 12AX7 have more bass response than an NOS Jan 12AX7 or would the plate voltage of a given tube make the tonal difference?
In simplistic terms, does the gain or the plate voltage make the difference in tone or does the valve position..as related to the tone stack?
I know..I'm probably over-thinking and Mesa amps are stock all 12AX7 tubes, but everyone tweaks their preamp tube cocktails..
Just some Sunday wonderin'..:rolleyes:

[dplight]

Casper, I've seen preamp designs that put the plate as low as 50V on a 12AX7 and and going up to the 200-300V range. I think the lower voltages are to make the tube distort at a lower gain and to make it to make it less linear along it's operating curve. It's commonly called a "starved plate" design and is used a lot in solid state/tube hybrid gear where the tube is just there to add it's mojo to the sound.

[tom]

I thought your question was about the tonal difference a particular Tube would have in your amp, not what circuit design parameters make tonal changes. If you're talking about design parameters like how much plate voltage the circuit puts to the tube you are way out of my scope of knowledge.

[Casper]

I should have provided a little background. From what I've read, the V2 position on my Blue Angel is the most important tube position in the amp and dictates the tone. I have a 12AT7 there now and it apparently is fine. Wanting the amp to be its best..and wanting a little more low end, I was wondering if a particular 12AX or AT or even AU would be able to give me more lows..and I didn't know whether that came from the tube 'type', gain or plate voltage...
sorry folks... but thanks so far! :)

[pipedwho]

The different tube types AT/AX/AU/AY,etc not only have a different effective gain structure, but also have a different output impedance. The AX7 is the highest impedance tube (and also the highest gain in the right circuit), the AU7 is the lowest impedance (and usually the lowest gain). But, the circuit design must be matched to the tube to maximise the performance (in gain and frequency response).

If a circuit is designed for an AU7 tube, substituting it with an AX7 may not increase gain. It is possible that the AX7 will be unable to drive the heavier expected load and become 'muffled'.

The AT7 is a good low impedance drive tube, and works well when a strong drive is required. But, that being said, sometimes having a non-ideal match and muffling the low/high frequencies with faster breakup (higher gain) is a desired characteristic within a particular gain stage, and in that case an AX7 could work better. It really does heavily depend on the circuit design around the tube, and on how any given stage relates tonally to the other gain stages in the amp.

The tone shaping of each stage in a tube amp is generally done with a specific tube in mind, but some people will prefer a slightly different response. Changing the tube (brand and/or type) is an easy way to experiment with this.

If you preferred the bass response of the AT7 over the AX7, then it would be worth trying an AU7 in that position. It won't have the same gain structure, but it will provide a lower impedance, and depending on the circuit it's in, that may be sufficient to give you that extra punch. OTOH, if the tube impedance of the AT7 is already at the ideal match (for your preferred bass response), the AU7 may go the other way. No guarantees either way, but definitely worth a try.

[Casper]

Thanks Piped..always insightful my friend..
That gives me direction..