whats the purpose of using half a duel triode and have 2 tubes instead of 1?

Looking over a tube crossover schematic. The designer choose to use only half of the duel triode tubes, 12ax7. At first i thought this was just to make the schematic easier to read by showing each triode wired individually. However looking at the circuit boards, there are 4 tubes instead of wiring both sides of the dual triode which would lower the total # of tubes needed per channel.

Does this offer any advantages?

is it a dual crossover and the other tube 1/2 is used for the other channel?  Maybe HOPING the triodes are matched in each bottle and matched between sides?

Gus said:

is it a dual crossover and the other tube 1/2 is used for the other channel?  Maybe HOPING the triodes are matched in each bottle and matched between sides?

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It is a duel channel crossover however each channel uses 4 12ax7's and half the triode per tube.  In other words each channel has 4 triode stages and uses  4 12ax7's per stage instead of wiring up the other triode in the tube and having 2 per stage. Maybe that is what they are hoping for. Maybe they want to sell more tubes in the retube box?

Probably to avoid interaction between the two triode sections inside one tube.

chrissugar

chrissugar said:

Probably to avoid interaction between the two triode sections inside one tube.

chrissugar

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yes but isn't that what the screen is for?

Just guessing: crosstalk between two different tubes may be better than crosstalk between two tridoes in one bulb

> which would lower the total # of tubes needed per channel.

And that would be BAD, because it reduces the selling price.

In the world of 5-tube radios, 7-tube and 13-tube radios sold for more.

PRR said:

> which would lower the total # of tubes needed per channel.

And that would be BAD, because it reduces the selling price.

In the world of 5-tube radios, 7-tube and 13-tube radios sold for more.

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sadly it's probably nothing more serious then that.

pucho812 said:

PRR said:

> which would lower the total # of tubes needed per channel.

And that would be BAD, because it reduces the selling price.

In the world of 5-tube radios, 7-tube and 13-tube radios sold for more.

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sadly it's probably nothing more serious then that.

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+1

On the other hand, we could also imagine, that they need severe selection/matching of their tubes, then nowadays, it's easier to find one half of a 12AX7 which pass the selection process than a twin...

Axel

All bland answers...

There's two of them so that the microphonics are generated in STEREO!!!

I just thought that maybe just maybe there was some real design mojo going on instead of

look we have more tubes per channel

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Eh... you're missing the point completelly...

It's plain obvious, that in tube "A", the "left" triode is used, and vice-versa, in tube "B", the "right" triode is used.

So, if/when they wear-off, you simply swap both tubes, and you have a "fresh power" in your box again.

Imagine, it's like just having a spare-tire in your box!! Swap'n'drive!!



(I should patent this asap.. before it gets "copied")

pucho812 said:

It is a duel channel crossover however each channel uses 4 12ax7's and half the triode per tube. In other words each channel has 4 triode stages and uses 4 12ax7's per stage instead of wiring up the other triode in the tube and having 2 per stage. Maybe that is what they are hoping for. Maybe they want to sell more tubes in the retube box?

Click to expand...

Have you checked if perhaps the "unused" triode-half will be put into action, when/if you change/swap them from one socket to the other within the crossover ?? ( If wired like this, it will save you on tube-money.) But anyway - small-signal tubes will last for years and years - unless someone drops the crossover by accident or smack it with a hammer. Only output-tubes like those in the power sections of guitar/bass-amps will actually wear out

(W., you're replying to a 14years old thread - it's almost old enough to buy its own beer)

Ah thank you ! ( But those tubes should still be good - and maybe, by now, the crossover has turned Vintage !