I've been experimenting with various tubes lately and the 12AV7 has a bad reputation in home audio. Maybe for being non linear?
Was curious to see how it sounded.
Took some adjustments. First time was awful. But then some tweeks and wow.
Playing some Metallica with this configuration really impresses me. Huge presence, power, bass, punch, and more.
Maybe the 5687 is better for the softer music, wasn't impressed using this for heavier music.
Let me know if anyone want to try this:
Some NOS GE 12AV7's. Nice glow also.
Was curious to see how it sounded.
Took some adjustments. First time was awful. But then some tweeks and wow.
Playing some Metallica with this configuration really impresses me. Huge presence, power, bass, punch, and more.
Maybe the 5687 is better for the softer music, wasn't impressed using this for heavier music.
Let me know if anyone want to try this:
Some NOS GE 12AV7's. Nice glow also.
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Brit01 said:
No maybe's about that. You didn't specify operating points on that schemo, but it looks like this loadline ought to come pretty close Loadline. Typical hideous 12AV7 loadline, and 10% THD is more like BJT territory than vacuum tube. Of course, it gets better if you can keep the output swing below the max Vop-p. White cathode follower operation isn't so critical, but you can do a helluvalot better for the first gain stage. If you need a sinfgeton triode there, trioding a pent like the 6AU6, 6SJ7, etc. would be a better way to go.
12AV7s might be the cheapest 12A*7 type (WHUDDA SURPRISE!
) but there are duals that are even cheaper and more linear as well.Still, if you can get the durn things actually sounding good, then you've really accomplished something. I'm definitely not one to fall for audiophool fads in either tube types or topologies, and have used VTs without any audiophool pedigrees, both in small signal and power applications. Lots of "sleepers" out there that don't command audiophool prices. .
Either you're using the wrong pinout diagram, or you was had. 12AV7s are all dual heater and center tapped for either 6.3V or 12.6V operation, just like the rest of the 12A*7 family. There's a 6.3V only version of the 12AX7, but they certainly don't call it a 12AX7
Brit01 said:Maybe the power/punch I'm hearing is actually the distortion
That's very possible. Distortion isn't all created equal, and certainly contributes to the sound. The h2 that SETs produce (especially if they don't employ gNFB to reduce it) definitely contributes to how these sound. That applies in spades to guitar amps where that "Fender sound" or the "Marshall sound" is pure distortion.
As for how 12AV7s actually sound, that depends on what the distortion profile looks like. Based on a lot of on-line comments, it would seem that these produce mainly h2. "Dark" is how it's frequently expressed, and that means too much h2.
You still haven't said how much output this preamp is designed to supply. If it isn't more than a volt or two, the resulting distortion will be less for the lower output swing, will not be excessive, and may be making for a nice effect when playing Metal.
Then I think I was had then. I'll post pictures of my particular specimens.Miles Prower said:
12AV7s might be the cheapest 12A*7 type (WHUDDA SURPRISE!
Either you're using the wrong pinout diagram, or you was had. 12AV7s are all dual heater and center tapped for either 6.3V or 12.6V operation, just like the rest of the 12A*7 family. There's a 6.3V only version of the 12AX7, but they certainly don't call it a 12AX7
About the loadline distortion: It looks to be mostly 2nd harmonic, am I right? I use some 12AV7-types (5965's) in LTP with a constant current source, with the assumption that the differential topology should cause this distortion to cancel out.. right?
There aren't that many dual triodes with the essential characteristics of highish gain, lowish plate resistance, and low cost
sorenj07 said:
Most triodes produce mainly h2. Some of the types with high u-factors can produce more h3 under some loadlines. For 12AV7s, it looks like these do produce mainly h2. If you used them in an LTP with active tail load, then the balance would cancel most of that distortion.
There aren't that many dual triodes with the essential characteristics of highish gain, lowish plate resistance, and low cost
I tend to favor 6BQ7s for those very characteristics. However, these like to see unusually high Vpk's in order to show good linearity, so you'll need to have the DC to get that voltage up (or use an active plate load). Also, beware of the 6BQ7s with series connected heaters as these can be terribly microphonic. The ones with parallel connected heaters seem to be much better in that regard. The Sylvania's with the series heaters ring like bells, but the parallel heater Sylvania's and Motorola's are nice and quiet.
Arnulf said:
1) Av is voltage gain. It's a commonly used symbol for voltage gain.
2) Vave= (Vp(max) + Vp(min)) / 2 (Average value of the max and min output voltages)
THD= [ (Vave - Vpkq) / (Vp(max) - Vp(min)) ] X 100
That's the graphical estimate for h2. It doesn't take into consideration higher order harmonics, and estimating those graphically is so tedious you could breadboard the circuit and measure directly in the same amount of time. Also beware that graphical THD estimates tend to run high. Still. it gives a good idea as to what to expect so far as linearity is concerned.
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