Hello,
I planning on building a WE91A clone for my next project and need help deciding on which pentode to use.
The practical side of my brain says 5693 (Pros: octal socket, 6.3V heater)
The exotic side of my brain says WE310A or WE328A (Pros: like the original and it looks cool)
The high tech in says Siemens C3M (Cons: not really WE91A clone, 20V heater, loctal socket….. But can run at high current to avoid “skew rate” issues)
So what would you folks recommend?
My second question is what current to run the 5693/310A at.
The WE91A is set at 2mA plate current.
From what I can tell from the datasheet, running this tube at 5ma (plate) produces a lot lower 2nd harmonic distortion, at the cost of a lower Av.
Any recommends on the operating point of the 5693/310A?
I planning on building a WE91A clone for my next project and need help deciding on which pentode to use.
The practical side of my brain says 5693 (Pros: octal socket, 6.3V heater)
The exotic side of my brain says WE310A or WE328A (Pros: like the original and it looks cool)
The high tech in says Siemens C3M (Cons: not really WE91A clone, 20V heater, loctal socket….. But can run at high current to avoid “skew rate” issues)
So what would you folks recommend?
My second question is what current to run the 5693/310A at.
The WE91A is set at 2mA plate current.
From what I can tell from the datasheet, running this tube at 5ma (plate) produces a lot lower 2nd harmonic distortion, at the cost of a lower Av.
Any recommends on the operating point of the 5693/310A?
The first WE91's indeed used a 6C6.
I tried a bunch of these pentodes as 300B drivers. My favorite was the 6J7G. I preferred it over the C3m. Two recommendations:
Use an OC3 to regulate the screens.
And use the smallest plate resistor you can get away with on the pentode. I had a fairly high output CDP at the time and I think I still had enough gain with half the size of what WE used.
Don't forget to recalc the operating point if you change the resistor! And up the plate current a little, but not too much. One thing I found is that generally I liked pentodes that liked to run at 3-5ma plate current better than those running 10ma and above. An exception was the 6SG7. It sounded really nice at 10ma, but you must choose an operating point that stays well away from the remote cutoff region.
I only tried octals and the C3m. I got bored and went onto something else before the miniatures made it to the table.
I tried a bunch of these pentodes as 300B drivers. My favorite was the 6J7G. I preferred it over the C3m. Two recommendations:
Use an OC3 to regulate the screens.
And use the smallest plate resistor you can get away with on the pentode. I had a fairly high output CDP at the time and I think I still had enough gain with half the size of what WE used.
Don't forget to recalc the operating point if you change the resistor! And up the plate current a little, but not too much. One thing I found is that generally I liked pentodes that liked to run at 3-5ma plate current better than those running 10ma and above. An exception was the 6SG7. It sounded really nice at 10ma, but you must choose an operating point that stays well away from the remote cutoff region.
I only tried octals and the C3m. I got bored and went onto something else before the miniatures made it to the table.
It's a voltage stabilizer tube.
See here
Right name is 0C3, not OC3. The first letter specifies the heating voltage as we all know. And because a voltage stabilizer has no heater, it has accordingly zero heater voltage. This explains the Zero as first letter.
Pentodes need a very tight screen voltage. It should be "locked" to the cathode. This can be done with a big cap, or better with a regulator valve. Unfortunatly these can be noisy.
Regards, Simon
See here
Right name is 0C3, not OC3. The first letter specifies the heating voltage as we all know. And because a voltage stabilizer has no heater, it has accordingly zero heater voltage. This explains the Zero as first letter.
Pentodes need a very tight screen voltage. It should be "locked" to the cathode. This can be done with a big cap, or better with a regulator valve. Unfortunatly these can be noisy.
Regards, Simon
OK, let’s see if I got this 0C3 voltage regulator right.
B++ is 370V
The 0C3 needs at least 5mA, G2 of the pentode needs .9mA. Let’s use 7mA to be safe.
The 0C3 replaces the lower resistor of the voltage divider, and the upper resistor must be adjusted to allow for the 5mA the 0C3 needs.
So 370V-105V = 265V 265V/7mA=37K 10W
Does this sound correct?
B++ is 370V
The 0C3 needs at least 5mA, G2 of the pentode needs .9mA. Let’s use 7mA to be safe.
The 0C3 replaces the lower resistor of the voltage divider, and the upper resistor must be adjusted to allow for the 5mA the 0C3 needs.
So 370V-105V = 265V 265V/7mA=37K 10W
Does this sound correct?
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