Need only one half of 12ax7

[Jalmeida]

Hey,

So looking into a build and I find myself needing only one half of a 12AX7. Can I just leave other half alone and not use? What to do with other half to not damage tube?

And I did look into single triode 12ax7 alternates, but looking for tubes in current production which kinda limits me.

[Dave]

You can leave one half unused with no problem.


Alternatively, you can parallel the two halves if that interests you.


Dave

[sluckey]

Hey,

So looking into a build and I find myself needing only one half of a 12AX7. Can I just leave other half alone and not use? What to do with other half to not damage tube?

And I did look into single triode 12ax7 alternates, but looking for tubes in current production which kinda limits me.

Just leave the grid, cathode, and plate of the extra triode unconnected. Wire the filaments as usual.

6AV6 and 6AT6 are single triode alternatives and are readily available very cheap.

[PRR]

current production

How many do you plan to kill? Golden-age 6AV6 and 6AT6 are stockpiled in quantities no one builder can use-up this lifetime.

[dude]

current production

How many do you plan to kill? Golden-age 6AV6 and 6AT6 are stockpiled in quantities no one builder can use-up this lifetime.

Do these tubes, 6AV6, 6AT6 have same gain as 12ax7..?

[sluckey]

One of them does. Look it up and tell me.   

     http://tdsl.duncanamps.com/tubesearch.php

[roarshock]

I've "converted' some radios to amps and built some amps. I've run across a  6AV6 a few times, and I've drooled over the Harvard schematic several times. Sluckey, you are genuinely enjoyed by many, I'm sure.  Thank you for teaching people to fish instead of feeding them for the day. With that in mind: Build someone a fire, they're warm all night, set someone on fire, and they're warm the rest of their life.

[kagliostro]

Only one thing

 If your amplifier is to be played at a big show consider that a 6av6 is not easy to find during a concert so be prepared to always have a spare part on hand

As for the other aspects.... good/perfect exchange with a 12ax7 triode

Franco

[pdf64]

… Just leave the grid, cathode, and plate of the extra triode unconnected. Wire the filaments as usual.
…

Assuming a typical 6.3V heater system, there seems no benefit in wiring up the heater of the unused triode?
And a downside, in that theoretically, after perhaps a few hundred hours of 0 current flow, the cathode might become poisoned and degraded.
Which isn’t an obvious issue, but we often swap valves around as part of normal troubleshooting. So it can be beneficial to keep the valve in good nick.

[kagliostro]

if I haven't a practical use for that unused triode I l'll  give a try to a paralleled configuration

may be it will result in a beneficial effect

Franco

[Jalmeida]

current production

How many do you plan to kill? Golden-age 6AV6 and 6AT6 are stockpiled in quantities no one builder can use-up this lifetime.

You’re probably correct on that. But there’s something to be said about having an easy to find tube in a pinch like the 12AX7 versus digging through someone’s NOS stash. 

[sluckey]

… Just leave the grid, cathode, and plate of the extra triode unconnected. Wire the filaments as usual.
…

Assuming a typical 6.3V heater system, there seems no benefit in wiring up the heater of the unused triode?
And a downside, in that theoretically, after perhaps a few hundred hours of 0 current flow, the cathode might become poisoned and degraded.
Which isn’t an obvious issue, but we often swap valves around as part of normal troubleshooting. So it can be beneficial to keep the valve in good nick.

There are a lot of Fender Bassman amps with heaters wired as usual and pins 1, 2, and 3 not connected.

[HotBluePlates]

... Golden-age 6AV6 and 6AT6 are stockpiled in quantities no one builder can use-up this lifetime.

If your amplifier is to be played at a big show consider that a 6av6 is not easy to find during a concert so be prepared to always have a spare part on hand

You’re probably correct on that. But there’s something to be said about having an easy to find tube in a pinch like the 12AX7 versus digging through someone’s NOS stash. 

You do you.

But I built an amp with a socket for 6AV6 or 6AT6, and bought a lifetime supply of each the about 10 years ago.  I think AES had them at the time for about the same $6 each they charge today, but a different vendor was selling for $3 each.  Spend the cost of two 12AX7, and you can buy 8-10 6AV6s.

All the tubes I bought were old U.S. from RCA and G.E.  A decade later, I still haven't needed to make the first tube-replacement in that socket.  Meaning maybe I have "2 lifetimes' supply"...

[bmccowan]

Does anybody who gigs, not carry a spare set of tubes? It's not like somebody can run to the nearest 7-11 and buy a 12ax7 or any other tube.

[Jalmeida]

Does anybody who gigs, not carry a spare set of tubes? It's not like somebody can run to the nearest 7-11 and buy a 12ax7 or any other tube.

Guitar Center carries 12AX7, rectifier and output tubes quite often. So do some of the independent music stores.

I think that buying a bulk lifetime supply of NOS 6AV6 is something i’d have no issues with doing. A musician friend who doesn’t even change their own tubes?? Most non-tech types? Probably not. I don’t disagree with the arguments for a single 6AV6 instead at all.

But I just was curious about using just one side of a dual triode. I will have to do some digging into parallel triode stages. Thanks for the help guys.

[dude]

One of them does. Look it up and tell me.   

     http://tdsl.duncanamps.com/tubesearch.php

T is 70% gain factor, the V is 100% gain factor

[sluckey]

One of them does. Look it up and tell me.   

     http://tdsl.duncanamps.com/tubesearch.php

T is 70% gain factor, the V is 100% gain factor

Yay!

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