ALternate NOS tubes in classic circuits

[jcool666]

Has anyone Ever tried to sub a 12AV7 in place of a 12AY7?

I built a 5E3 Deluxe a while ago but didn't have a Y for V1 so I put in a 12AX7 instead and put in a Blackface tone stack to tame the extra gain. It sounds okay but not right. So I was going to buy a brand new JJ 12AY7 from Antique Electronic Supply and use the X to make channel 2 into a distortion channel. But while I was browsing around I found a couple of NOS 12A tubes that got me to thinking. the 12AV7 has nearly the same gain as the Y but is asymmetrical with a bit more gain on the 2nd triode, (which would be the input stage on my distortion channel.) They also have the 12AZ7, which is close to a T in gain.

So I thought that if I used the 12AV7 as V1 and used the 12AZ7 in the high gain channel, I could have NOS tubes throughout my preamp and it'd only cost a buck or 2 more than the new-production JJ 12AY7. The bonus is that if the Z doesn't have enough gain for my taste I could drop in the X and find a use for the Z later.

Thoughts?

[thetragichero]

before dismantling it (terrible build quality, used the parts elsewhere) the 5e3 i made used 12av7 because at the time i had the same thought as you. seemed to work okay
nowadays i would plug the information into some of the calculators on the ampbooks sure to make sure everything is going as if expect it. at the time i just saw similar gain figures and decided it would work

[jcool666]

If it worked for you I'm just going to do it. So far I've had good luck with NOS tubes from Antique electronic supply. I got an amperex 6cm6 and an rca 12v6 for about 6 bucks each. While they wouldn't work for classic amps, custom builds are another matter and I cant complain about those brand names.

[Leo_Gnardo]

So I thought that if I used the 12AV7 as V1 and used the 12AZ7 in the high gain channel, I could have NOS tubes throughout my preamp and it'd only cost a buck or 2 more than the new-production JJ 12AY7. The bonus is that if the Z doesn't have enough gain for my taste I could drop in the X and find a use for the Z later.

Thoughts?

Won't hurt to give it a go. If you get a result you love, you'll have a unique tube lineup to boast about.

[Phil_S]

I bought a couple of NOS 12AV7 many years ago thinking they'd be an acceptable substitute for other 12A?7 tubes. My ears told me they are not. I don't have a technical background, so I'm not able to explain this very well. If you look at the data sheets, you'll see the 12AV7 has a plate resistance that is much more like a 12AU7. I believe the gain factor is only part of the picture. Ra is the other. The 12AV7 isn't really a close match to the 12AY7. The JJ 12AY7 is a $14 tube plus shipping. I suggest, if you've come this far, get the proper tube for the circuit. If you want to use the 12AV7, you'd probably benefit from a different cathode resistor and bypass cap choice. Of course, if you plug it in and you like it, that's good, too!

[jcool666]

I bought a couple of NOS 12AV7 many years ago thinking they'd be an acceptable substitute for other 12A?7 tubes. My ears told me they are not. I don't have a technical background, so I'm not able to explain this very well. If you look at the data sheets, you'll see the 12AV7 has a plate resistance that is much more like a 12AU7. I believe the gain factor is only part of the picture. Ra is the other. The 12AV7 isn't really a close match to the 12AY7. The JJ 12AY7 is a $14 tube plus shipping. I suggest, if you've come this far, get the proper tube for the circuit. If you want to use the 12AV7, you'd probably benefit from a different cathode resistor and bypass cap choice. Of course, if you plug it in and you like it, that's good, too!

After taking a closer look at the datasheets I saw that the plate current, plate resistance and transconductance more closely match the T instead of the Y. I'm now starting to wonder if you couldn't use a V as a cathodyne phase inverter. That might be something I'll play around with, but not in this amp. the phase inverter works and I don't want to mess with it.