Preamp Tube Experiments

[KH Guitar Freak]

Interesting. The only valves I have replaced in my Roadster are the poweramp valves and the V1 preamp valves. The former being Winged C 6L6s, and the V1 preamp is the Mesa SPAX7 preamp valve. The latter made my amp just a tad tighter, with perhaps more headroom and less noise (maybe better dynamics as well???). Nevertheless, the Winged C 6L6s improved my tone overall, bar perhaps consistency and reliability if I replaced them with another quad of Winged C 6L6s...

Speaking of fizz, a lot of it goes away if you actually run a good power conditioner through your rig. I cannot stress enough the massive improvement you'll get from a good power conditioner. In fact, it arguably gives you a better bang for your buck in terms of rig improvements...

 

[ltd2recto]

this is a great read... I'm still getting my head around it. Do you think this applies to other Mesa amps like the rectifier series?

It would be interesting to try this on say a 3 channel DR and see if V1, V2 and V3 work in the same manner. I would assume they would be similar but not the same because if you play one of them stock side by side with a stock roadster there are differences right off the bat. So the principle of it may be the same but i have a feeling V1 would play an even bigger role in a standard DR/TR like they do with the 2 channel DR and TRs.

Maybe one of the tube guru's can chime in as I a definite newb with exerimenting with the preamp and knowing more about the design.

I'm not a tube guru but I found my single recto works the same way. V1 - trbele, V2, mids, V3 - bass. To tame the fizz I use a JJECC83s in V1.

 

[MrMarkIII]

The manuals, available at Mesa's website, have charts detailing what each tube does:
Dual and Triple, Two Channel:
http://www.mesaboogie.com/manuals/2chRecto.pdf
Dual and Triple, Three Channel:
http://www.mesaboogie.com/manuals/3chRecto.pdf

Or:
2 Channel Recto:
V1 A= Input Stage
V1 B= Not Used
V2 A= 2nd Stage
V2 B= 3rd Stage
V3 A= 4th Stage
V3 B= 5th Stage
V4 A= FX Send
V4 B= FX Return
V5 A & V5 B= Phase Splitter /Output

3 Channel Recto:
V1 A=Input Stage all 3 Channels
V1 B= Clean Channel
V2 A= 2nd Input Stage all Channels
V2 B= Channels 2 & 3 Boost Stage
V3 A= Channels 2 & 3 Boost Stage
V3 B= Same as V3 A
V4 A= FX Send
V4 B= FX Return
V5 A & V5 B= Phase Splitter / Output

Looking at the rear of the chassis, V1 is the 12AX7 furthest to the right, closest to the input jack. Each 12AX7 contains two amplifying elements, for example, V1 A and V1 B.
Hope this helps

 

[boogiewoogie]

Mesa Boogie Road King II Tube Functions

V1 A= First Gain Stage
V1 B= Second Gain Stage
V2 A= 3rd Gain Stage - Ch 1 & 2
V2 B= 3rd Gain Stage - Ch 3 & 4
V3 A= 4th Gain Stage - Ch 3 & 4
V3 B= Tone Stack Driver - Ch 3 & 4
V4 A= Reverb Return
V4 B= Reverb Driver
V5 A= FX Loop Send
V5 B= FX Loop Return
V6 A & V6 B= Phase Inverter/Driver

I haven't changed a single tube since I got this amp... the only issue I have with it is that I want it to be a tad more tight with less flub.... and more singing, warm leads with sustain... I can accomplish this to a degree with the xotic bb preamp... if I could improve things even more with new tubes then I definitely would give it a shot... the only problem is that some of those tubes jdurso mentioned are quite expensive heheh

 

[boogiewoogie]

Hey Jdurso

It's been a long while since anybody posted on this great (dead? I hope not) thread. How is everything going with those NOS tubes? Did you change any of them? I'm tempted to pull the trigger and go tube hunting at evilbay!!
Before I said those NOS tubes are expensive...why should that be a problem, hell I have Roadking II after all! :twisted: :lol:
My only concern with these NOS tubes is tube life. It's been 3-4 years and I never ever changed a single tube on my Road King II and it still kicks ass. Those mesa tubes are very reliable. I don't want to blow a lot of money for these NOS little tone bottles and have them crap out on me a month later, but maybe I'm just talking out of my ass... I don't know
Please chime in!

 

[TremoJem]

Pre-amp tube gain factors explained here;
http://thetubestore.com/gainfactor.html

Many people associate "headroom" with "low gain", but it's not exactly same thing.
Headroom really means, "How loud can I turn up the power section before it starts to distort?"
A 100 watt amp has more "headroom" than a 20 watter, regardless of the distortion supplied by the pre-amp tube(s).
Replacing a 12AX7 (gain factor = 100) with a 5751 (gain factor = 70) will give you 30% less pre-amp gain. This means that if you get a particular lead-type sound with the gain knob on "7", you now need to turn the knob up to "10" to get the same level of distortion.
However, your amp doesn't get louder.

Please elaborate. For example how or what does one do or use to get more "headroom"?
If I swap a 5751 for a 12AX7 in V1 how does this affect: the amp individual channel volume, the output tubes (do they end up working harder and breaking up to introduce output stage break up), the over all tone if applicable.
I use channel two on my Tremoverb in the Modern mode. I generally have my gain maxed (I know... I suck). The problem I have is that my channel master is barely freaking on. I would love to have the channel master at about 20%-25% rather than 5%-10%, but to get the gain I like from the gain knob, it is too loud.
Thanks Brother.

 

[TremoJem]

Interesting. The only valves I have replaced in my Roadster are the poweramp valves and the V1 preamp valves. The former being Winged C 6L6s, and the V1 preamp is the Mesa SPAX7 preamp valve. The latter made my amp just a tad tighter, with perhaps more headroom and less noise (maybe better dynamics as well???). Nevertheless, the Winged C 6L6s improved my tone overall, bar perhaps consistency and reliability if I replaced them with another quad of Winged C 6L6s...

Speaking of fizz, a lot of it goes away if you actually run a good power conditioner through your rig. I cannot stress enough the massive improvement you'll get from a good power conditioner. In fact, it arguably gives you a better bang for your buck in terms of rig improvements...

O.K., I'll bite...I have been considering this for awhile.

What do you use?

Is it a conditioner or regulator?

Thanks Brother.

 

[TremoJem]

Mesa Boogie Road King II Tube Functions

V1 A= First Gain Stage
V1 B= Second Gain Stage
V2 A= 3rd Gain Stage - Ch 1 & 2
V2 B= 3rd Gain Stage - Ch 3 & 4
V3 A= 4th Gain Stage - Ch 3 & 4
V3 B= Tone Stack Driver - Ch 3 & 4
V4 A= Reverb Return
V4 B= Reverb Driver
V5 A= FX Loop Send
V5 B= FX Loop Return
V6 A & V6 B= Phase Inverter/Driver

I haven't changed a single tube since I got this amp... the only issue I have with it is that I want it to be a tad more tight with less flub.... and more singing, warm leads with sustain... I can accomplish this to a degree with the xotic bb preamp... if I could improve things even more with new tubes then I definitely would give it a shot... the only problem is that some of those tubes jdurso mentioned are quite expensive heheh

Tremoverb/Road King II

V1A - first gain stage/First Gain Stage
V1B - reverb return/Second Gain Stage
V2A - second gain stage/Gain Stage - Ch 1 & 2
V2B - third gain stage (split-load, although output is from plate only)/3rd Gain Stage - Ch 3 & 4
V3A - fourth gain stage/4th Gain Stage - Ch 3 & 4
V3B - tone stack driver (cathode follower)/Tone Stack Driver - Ch 3 & 4
V4A - FX loop return/Reverb Return
V4B - FX loop send (cathode follower)/Reverb Driver
V5A - reverb driver/FX Loop Send
V5B - post-FX loop gain recovery stage/FX Loop Return
V6A & B - phase inverter/Phase Inverter/Driver

Hoping for some similarities...oh well.