Otl

[dhaen]

how complicated and oversized most OTL designs are

Some of that seems to be to stabilize the output votage, so you can throw away the ouput cap.

Would 470K be enough leak to hold all those 6080's down?

I meant that each valve has a minimum recommended leak value, so it doesn't go "runnaway". When you parallel valves, I would think that value should be divided by the number of valves - though I could be worng..

 

[Joel]

I think you're confusing that with something else.
The data sheets I've seen only have maximum values for the grid resistor when used with cathode bias or fixed bias (1M, and 100k respectively).

 

[fdegrove]

RIGHT SAID FRED.

Hi,

How obvious can it be?

I would think that value should be divided by the number of valves - though I could be worng

Yes....I agree....number of valves or better numcer of triodes //'ed.

Complicated or what?

 

[dhaen]

I've seen only have maximum values for the grid resistor when used with cathode bias or fixed bias

Oh no!
I know I'm right here. They're max values of R, to make min values of I...
You can use 10 ohms (if you can drive it)

 

[Joel]

a) there's no current in the grid circuit, is there? So, why divide down the resistance value?
b) Lowering the value lowers the stage gain of the previous tube, and forces you to use a bigger coupling cap before the power stage.

 

[fdegrove]

SPREAD THE WORD...

Hi,

So, why divide down the resistance value?

Assume a recommended gridleak R of 500K...now if one // the two how about the gridleak R now?

Guys wake up please,

 

[dshortt9]

a. Where there is voltage, there is resistance and current. Ohm's law...

b. Fact of life we live with.

 

[dhaen]

There's no measurable current (for IHT'S anyway) until the moment of runaway.
I suppose it depends on whether the valves runaway at the same time or not

Lowering the value lowers the stage gain of the previous tube

Yes. That's why we choose the highest allowed / safe value.

In older days, there was also the leakage of coupling caps to contend with.

 

[dhaen]

Where there is voltage, there is resistance and current. Ohm's law...

Disagree.
Voltage is the only one that can exist in isolation.

 

[Joel]

a. Where there is voltage, there is resistance and current. Ohm's law...

So, I suppose a battery sitting on my desk has zero voltage potential - since there is no current flowing???

 

[fdegrove]

SO WHAT?

Hi,

Better read the datasheets carefully.

Brrrr,

 

[dshortt9]

A tube always has some input impedance. Whether it is 1 meg,10 meg, or 100 meg there is current flow.

 

[dshortt9]

There may be many gigaohms resistance between terminals but there is current flow.

 

[fdegrove]

YEPPIE

Hi,

A tube always has some input impedance. Whether it is 1 meg,10 meg, or 100 meg there is current flow.

Remember that volpot anyone?

Cheers,

 

[Joel]

Re: SPREAD THE WORD...

Assume a recommended gridleak R of 500K...now if one // the two how about the gridleak R now?

Frank, Rg is not a "gridleak"... this is the same thing we were discussing yesterday. The 6080's are cathode biased. The cathode is referenced to ground, and raised postive by the resistor in series with it. Meanwhile, we need to also reference the grid to DC ground so it will "see" the cathode as postive... we do this with a resistor. The resistor also happens to be a load for the previous tube, so we make it big, in order to not lose a lot of signal.

Is there still confusion??

 

[Joel]

There may be many gigaohms resistance between terminals but there is current flow.

And as I said in a previous thread there also is capacitance between my amp and Jupiter... do I care???

 

[fdegrove]

PHYSICS

Hi,

And electrons are going to flow the way you tell'em to?

Joel...physics are physics you know.


I read that book too,

 

[dshortt9]

When lightning decides to strike from Jupiter to Earth I guess. Ha!

 

[Joel]

Re: PHYSICS

And electrons are going to flow the way you tell'em to?

What does that mean?

 

[dhaen]

A tube always has some input impedance. Whether it is 1 meg,10 meg, or 100 meg there is current flow.

I think the reactive component (C - Miller)exceeds any perceived resistance that might occur due to spacecharge.
So in the absence of a grid leak R, you're just charging and discharging a few pf's.

To reiterate:
I don't believe that any current flows through the grid leak resistor, except at startup, and in the case of current runaway.

I'd be interested to be proven wrong