Tube for high input Z

[Wavebourn]

Interesting that it's run as a triode.

It's run as a pentode with equal voltages on plate and screen grid, wired as a cathode follower. Well, suppressor grid tied there too.

As I said before, another pentodes, like 6J1P, work in such schoolbook arrangement like a charm. You can buy a Ziploc of them for the price of Edamame.

 

[SY]

No, it's a triode. The screen does not swing with the cathode.

 

[Wavebourn]

No, it's a triode. The screen does not swing with the cathode.

Does screen swing with cathode in cathode biased stage? When I apply a global negative feedback to cathode of the 1'st pentode in my amp, is it triode connected?

 

[SY]

If cathode and screen are at the same AC potential, it's a pentode. If the plate and the screen are at the same potential, it's a triode.

A pentode CF would look like the attached.

 

[SY]

When I apply a global negative feedback to cathode of the 1'st pentode in my amp, is it triode connected?

In most amps with a pentode input stage (e.g., Dynaco, Mullard 5-20...), the screen is bypassed to the cathode, not to ground.

 

[Wavebourn]

In most amps with a pentode input stage (e.g., Dynaco, Mullard 5-20...), the screen is bypassed to the cathode, not to ground.

So in my amps they are what? They are bypassed to ground.

Neither to anode, nor to cathode.

How would you call them?

 

[Michael Koster]

I think if the g2-cathode voltage swing is approximately equal to the plate-cathode or output signal swing, it's going to follow the triode characteristic.

By contrast, a pentode follower would swing g2 with the cathode, much like a cascode or triode ACF would swing the plate with the cathode. I have a sketch of one of these I'd like to try...

I vote "triode".

Oops lots of posts... SY has the pentode version in #44.

 

[Wavebourn]

Let it be a Steerode: between Pentode and Triode Steering.

Hmmm... Sounds tasty! "I use Steerodes in my amp; they sound bright, strong and creamy!"

 

[SY]

Think of UL, where the screen swing lies between plate and cathode. Is it pentode or triode?

 

[Wavebourn]

Think of UL, where the screen swing lies between plate and cathode. Is it pentode or triode?

Still the same Steerode, of course!

(Hmmm... time to correct my Firefox's dictionary.)

 

[Sch3mat1c]

Screens bypassed to ground with unbypassed cathodes will produce UL behavior. As plate falls, cathode rises, so G2-K voltage falls, but not as much as A-K.

It doesn't matter if the cathode is driven by something else (like NFB) or itself, cathode voltage is cathode voltage.

Tim

 

[Wavebourn]

Screens bypassed to ground with unbypassed cathodes will produce UL behavior. As plate falls, cathode rises, so G2-K voltage falls, but not as much as A-K.

It doesn't matter if the cathode is driven by something else (like NFB) or itself, cathode voltage is cathode voltage.

You know Tim; Steerode sounds better for me than UL. UL is associated with taps in output transformer, while Steerode may be used as a common name that includes UL.

 

[Sch3mat1c]

Gee, and I was thinking you went and stuck electrodes on a bull!

 

[Wavebourn]

Gentlemen;
does anybody have a schematic of Altec M21D?

Does the mike have some resistors inside, or a tube only?