I came across Dennis Grimwood’s article (link below) about triode strapped Pentodes/Beam Tetrodes and then did a forum search and can see that some of his suggestions have been discussed before but didn’t see much on the two subjects I am interested in.
He describes Triode operation using G2 as control grid and G1 connected to cathode. He says it needs more drive and more negative bias but behaves more like a true triode than the conventional approach of triode strapping a pentode with G2 connected to the plate with a 100ohm resistor. I was wondering if anyone had tried or has any thoughts on the theory and roughly how much extra bias and drive it is likely to need. The acticle mentions Class B drive, but that doesn't make sense to me if more -ve bias is required. I'm mainly interested in class A1 A2 single ended.
I did see posts about Screen Drive/Crazy Drive but gather that’s a different connection or maybe I am getting 😕
The other suggestion of Mr Grimwood’s that caught my eye is the diode between G2 and anode when using the conventional approach of triode strapping G2 to anode. Would I be right in thinking that in this application the negative half of the amplified ac signal on G2 would be blocked but the positive half of the amplified signal on G2 would pass through the diode ? It’s not clear to me whether there is any benefit in blocking the ac component of G2 and if there is wouldn’t it be better to use a suitable choke perhaps with an appreciable DCR to also help reduce the dissipation on G2.
Link
Tubes
He describes Triode operation using G2 as control grid and G1 connected to cathode. He says it needs more drive and more negative bias but behaves more like a true triode than the conventional approach of triode strapping a pentode with G2 connected to the plate with a 100ohm resistor. I was wondering if anyone had tried or has any thoughts on the theory and roughly how much extra bias and drive it is likely to need. The acticle mentions Class B drive, but that doesn't make sense to me if more -ve bias is required. I'm mainly interested in class A1 A2 single ended.
I did see posts about Screen Drive/Crazy Drive but gather that’s a different connection or maybe I am getting 😕
The other suggestion of Mr Grimwood’s that caught my eye is the diode between G2 and anode when using the conventional approach of triode strapping G2 to anode. Would I be right in thinking that in this application the negative half of the amplified ac signal on G2 would be blocked but the positive half of the amplified signal on G2 would pass through the diode ? It’s not clear to me whether there is any benefit in blocking the ac component of G2 and if there is wouldn’t it be better to use a suitable choke perhaps with an appreciable DCR to also help reduce the dissipation on G2.
Link
Tubes
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David Bernings patent of 1976
http://davidberning.com/images/patent3995226/DB-patent3995226.pdf
Best regards, Frank
http://davidberning.com/images/patent3995226/DB-patent3995226.pdf
Best regards, Frank
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Yea, triode with amplification factor of 1.5 or so.
Diode between plate and screen is nonsense.
His ideas about voltage rating of triode-connected pentode is also nonsense.
Diode between plate and screen is nonsense.
His ideas about voltage rating of triode-connected pentode is also nonsense.
yes, screen drive it is
to drive through G2 you have to bias G2 positive not more negative
and you have to drive the variable screen current, so you need cathode follower or mosfet source follower as driver
a basic description and example in this article may help you further:
www.frihu.com/images/2019/10/tech-bulletin33.pdf
crazy drive is more sophisticated, both grids are driven
a diode does *NOT* block AC, when forward biased it conducts current thereby dropping a few hundred mV and passes *all* AC, unless it becomes reverse biased in which case it blocks both ac and dc
a diode between plate and g2 will always have to be forward biased and conduct, as a pentodes plate current would drop to near zero without g2 current ...
to drive through G2 you have to bias G2 positive not more negative
and you have to drive the variable screen current, so you need cathode follower or mosfet source follower as driver
a basic description and example in this article may help you further:
www.frihu.com/images/2019/10/tech-bulletin33.pdf
crazy drive is more sophisticated, both grids are driven
a diode does *NOT* block AC, when forward biased it conducts current thereby dropping a few hundred mV and passes *all* AC, unless it becomes reverse biased in which case it blocks both ac and dc
a diode between plate and g2 will always have to be forward biased and conduct, as a pentodes plate current would drop to near zero without g2 current ...