What's wrong with the 12AV7? Try this out!

[Brit01]

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.

[sorenj07]

My problem with a sleeve of Raytheon 12AV7's is that the filament isn't centertapped

[Brit01]

ah yes, this also has a line out to use as a linestage. Some RTI 1uF as coupling caps.

[thoriated]

My problem with a sleeve of Raytheon 12AV7's is that the filament isn't centertapped

Is it marked as a 12AV7? All the ones I have have the center tapped filament.

[kevinkr]

Originally posted by thoriated


Is it marked as a 12AV7? All the ones I have have the center tapped filament.

Mine too. Same pin out as all other 12A...7 series tubes.

[Brit01]

Bias question:

I have some yellow led's (2.0V I believe)
\

Interested in trying out the led bias system.

Could I incorporate in this design easily?

[kevinkr]

Originally posted by Brit01
Bias question:

I have some yellow led's (2.0V I believe)
\

Interested in trying out the led bias system.

Could I incorporate in this design easily?

Measure the voltage across the cathode bias resistors and if it is close you can substitute them for the bias resistors and caps.

[Miles Prower]

Originally posted by Brit01
I've been experimenting with various tubes lately and the 12AV7 has a bad reputation in home audio. Maybe for being non linear?

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. .

sorenj07
My problem with a sleeve of Raytheon 12AV7's is that the filament isn't centertapped.

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]

White cathode follower operation isn't so critical, but you can do a helluvalot better for the first gain stage

Maybe I can try a nice 5687 in the gain stage before the WCF.

Slight change in the pin connections on one of the 3 sockets and I'm all ready to go.
Would be good to compare.

Maybe the power/punch I'm hearing is actually the distortion

[Miles Prower]

Originally posted by Brit01
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.