Submini and regular 12a.7 tubes difference

[demym]

Hi,

does the fact that submini tubes (at least, those that have been used in this forum, like 6111, 6112, 6021, ecc..) have about 100V of maximum voltage, compared to the 4/500V of regular 12a.7, means also that they will work at their full capabilities with 80/100V ? (being near at their limit as the 12a.7 are with 400V)

That is, would a 6112 at 100V crunch in the same way a 12ax7 (or a 6112 mu equivalent) would at 200-400V range ? I keep seeing that submini guys almost replicate 'real' tube amp circuits, maybe with some minor adaptation.. This makes me thing so.

I am such wrong ?

Just trying to decide if building or not a NE555 199V thingie....

I've tried with 12AU/X/T7 at 80V (also with two double triodes, 4 stages !), but it seems to be very distant, as distortion emptity, from a normal 9V jfet emulation....(and i'm talking specifically about J201)... I bring in the discussion the fets because till now they are the devices that better suit my gain expectations.... i'm in a look for a modern heavy sound (i have a pinnacle kind of pedal that really satisfies me soundwise, especially in boost mode)

What minimum anode voltage should i reach to begin to hear some of this kind of sound ?

I didn't try yet a double valvecaster at 80V, but judging on the samples i've hear, even the triple valvecaster (with 12AU7) doesn't seem to be my sound..

is it right that turning a 220K trimmer on the plate the tube does the jfet biasing thing (that is, sound is better at 1/2 V+?)... that's what happens me on some ex-jfet circuits (rog style) when i plug the triodes into the ex-tansistor sockets...

interested only in having a good tubish preamp, not interested at the moment into the poweramp section

thanks, please be patient with my continuous need for information

have a nice time

[merlinb]

That is, would a 6112 at 100V crunch in the same way a 12ax7 (or a 6112 mu equivalent) would at 200-400V range ?

No, they are completely different devices. After all, a 12AT7 and a 12AX7 do not crunch the same, even when operating at similar voltages!

The voltages are largely irrelevant, what matters is the characteristics of the device; especially its grid current characteristics. To duplicate the sound of a conventional 12AX7 stage using a different device (whether valves, transistors or even opamps), you need to try and replicate the transfer characteristic. This is no mean feat. Subminis come close, since they are valves already, but they will always have their own characteristic crunch, unless you pull off some clever circuit tricks to force the whole circuit to mimic a 12AX7.

[petemoore]

interested only in having a good tubish preamp
  Every one is an experiment.
  Find a layout/schematic that is known to work with the tube and use it as a starting or ending point.
  As a starting point, observing schematics allows specific data to provide specific answers.
  A good choice has produced excellent end results, tried/true is imminently recommendable.
  Note that preamps tend to be picky about layout and power supply.
  Choosing the Eq is a lion's share of what make amp X able to, and bound to sound different than amp Y.
  Duncans Tonestack Calculator's ''interactive tone knob twistin'' graphic displays passive loss curves and instantly super learns the user about exactly what frequency/signal loss can be expected and what is allowed to pass various TC configurations [shows them too of course], an instrumental device when choosing what kind of eq to choose.
  Power supply is excellent starting point for a tube amplification unit, that type of tube seems like it should be excellent choice to use in a preamp design.

[PRR]

> sound is better at 1/2 V+?)...

Sound stops when plate is at ground or at B+. When you need an output that is not much smaller than the available supply voltage, you generally go to rough-center: 1/3rd to 2/3rd of supply voltage. The "optimum" depends on things you are not considering (and vacuum triodes are different than crystal JFETs). And with over 50V supply, you do not need "maximum" output to make guitar-level signals.

> 6111, 6112, 6021, ecc..) have about 100V of maximum voltage, compared to the 4/500V of regular 12a.7

12AX7, 12AT7, 12AU7 are rated 300V-330V, not 400-500V.

6111, 6112, 6021 all have a 165V rating. If you have a very critical task, where failure means death or disater and replacement is a problem, yes you should stay near 100V.... but stage-pedals are not that critical.

The tube does not see the full Supply Voltage. Some Fender preamps run 390V supply to the 12AX7. But the biasing and load leave only about 70% of that on the tube, 270V, which is within rating. Other Fenders run the same plan at 230V supply, about 161V on plate, which is legal on 6111, 6112, 6021.

All the classic tube crunches use 12AX7. None of the tubes you cite are much like 12AU7. The 6111 is low gain high current, and at any "good" condition won't distort a guitar. A "bad" condition of course will distort, but the classic amplifier stages are "good" designs over-driven.

As for your bigger question.... good "crunch" is more than dropping odd tubes into a JFET circuit. You can have a lot of fun trying, sure. But if you want to make music, the shorter path is to find some 300V and known-good circuits.