• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tubes to avoid

Status
Not open for further replies.
Jump to Latest
#44
RE:The comum grid stage...

Hi,

The comum grid stage...
Click to expand...

Nope, same circuit as before bar the gridleak resistor...it's tricky though and it's much easier just to use the resistor for I/V conversion but it can be done.

Don't waste your time looking for a solution, it's only obvious when you're having it right in front of you.

As I said I'm a bit of a tease and you're a bit like me so that's why...

Ciao,😉
 
#45
Something new...under the moon!!!

fdegrove said:
Hi,

Nope, same circuit as before bar the gridleak resistor...it's tricky though and it's much easier just to use the resistor for I/V conversion but it can be done.

Don't waste your time looking for a solution, it's only obvious when you're having it right in front of you.
Click to expand...


Can you clarify it...in the name of the "Science"!!!...

Arrivederci 😉
 
#46
RE:Something new...under the moon!!!

Hi,

Ah,ah...gotcha.

Something new...under the moon!!!
Click to expand...

There you have your answer...look out through the window, it is full moon isn't it?

No, the trick is to us the output impedance of the DAC as a gridleak for the tube.That only works if that impedance is reasonably linear across the band and very low.

Which is rarely the case, hence my remark that it's easier to use a gridleak of low value to do the I/V conversion.

Cheers Jorge,😉
 
#47
The powerfull grid!!!

fdegrove said:
Hi,
There you have your answer...look out through the window, it is full moon isn't it?

No, the trick is to us the output impedance of the DAC as a gridleak for the tube.That only works if that impedance is reasonably linear across the band and very low.
Click to expand...

Oui la Lune est trés belle aujourd'hui !!!

But how can the grid "suplly" the 1 or 2 mA that the DAC need??

A bientôt 😉
 
#48
LE MONDE A L'ENVERS.

Hi,

Eh,eh...

But how can the grid "suplly" the 1 or 2 mA that the DAC need??
Click to expand...

The grid doesn't supply anything, the DAC does the work.
I hope you understood it correctly from the start, it's the DAC feeding the tube stage not the other way around.

Cheers et a bientot quand-meme,😉
 
#49
The missing current....

fdegrove said:
The grid doesn't supply anything, the DAC does the work.
I hope you understood it correctly from the start, it's the DAC feeding the tube stage not the other way around.
Click to expand...


But the DAC for to work need to source or to sink 1 or 2 mA...where in this case they come from??



il ne faut jamais remettre au lendemain ce qu'on pourrait faire aujourd'hui.´😉
 
#50
NOTHING'S AMISS...

Hi,

Last one for tonight...

But the DAC for to work need to source or to sink 1 or 2 mA...where in this case they come from??
Click to expand...

The DAC sinks the current into the natural impedance that exists when the tube is added, i.e. the resistance between the grid and ground when the cathode of said tube is at ground potential.

As said it seems complicated, it is'nt and it doesn't always work well.
Just don't take it for something you can just do and get away with, I understand you want to get to grips with this but I certainly won't proclaim this as "good practice", I just wanted to get you thinking a little.
More importantly,I'd never put out any product made like this, it can "work", sort of.
From a designer POV see it as an exercise in engineering, not something you want to to market with, the balance is just too delicate.

il ne faut jamais remettre au lendemain ce qu'on pourrait faire aujourd'hui.´
Click to expand...

Absolutamente.😉
 
#60
stokessd said:
My shop "ears" currently go out to 100 Mhz. But the crappy ones stuck to the sides of my pie-hole seem to be pretty low bandwidth and really are only good to 18KHz or so. I want a refund.


The only real tubes to avoid are chinese power tubes (or they were to be avoided). A friend had fire shoot out of his Citation II because of chinese KT88's.

Sheldon
Click to expand...

Me too.. 😱 Other than that can't think of any tube that is not applicable to some application if you want it to be. FWIW, I can get 250kHz out of a 12AX7/ECC83, its only major problem really is the inability to drive a reasonable load directly, (aside from noise performance and miller capacitance) and as SY will explain that is easily fixed - and its quite linear. I've heard much worse, not that it is any sense a favorite of mine either.

Lots of people around here use 866A in big, high voltage DHT amps so a prior comment about its applicability is not true either.
 
Last edited:
Status
Not open for further replies.
Top Bottom