Drive Current for EL509 Enhanced Triode - Page 6

Andy Bartha · 13th February 2006, 05:38 PM

Wrenchone,
This amp is set as pentode with regulated screens. I'm sure it can be set up as triode but the amp is optimized for pentode. So some messaging will be needed to get the best sound for triode operation.

wrenchone · 13th February 2006, 07:35 PM

From the tube curves for the EL509, a screen driven triode amp will be a very different beast as compared to a pentode implementation, as a lot more voltage drive is required for significant output power, along with some significant screen current. I'm currently wrestling with how to do that while at the same time keeping the number of stages to a minimum.

Andy Bartha · 13th February 2006, 07:44 PM

Wrenchone,
No argument, I was just recommending the output transformer from Electra-Print. For a driver you could consider a mu stage. El-84 over a 6N1P or something like that. Svetlana had a tech tip showing this circuit. They said it could swing something like 350v which would be enough.

Tony · 13th February 2006, 08:40 PM

Andy,

thaks a lot.

Wrenchome,

have you seen david bernings' ut used 2x 12at7's and a 6cg7 tube complement.

wrenchone · 14th February 2006, 01:47 AM

I want to try and do my own circuit for this amp and not lean too heavily on other people's results.
I am very suspicious of using a mu-follwer in this application given the amount of drive voltage needed (at least 150V p-p). I don't see how someone could keep within the peak filament to cathode ratings of the tubes without using separate tubes for top and bottom and isolated filament supplies. At this point I'm thinking of using a pair of 6GF7 vertical oscillator/amplifier dissimilar triodes for amplification and follower duty. I may back this up with an 8CG7 for extra gain if needed. I I'm looking at using a differential pair at the input, maybe with cascode to get more gain, with a 400V regulated supply and about 250V at the plates.
I'll be using Hammond iron at the output, as is reasonably inexpensive and readily available - the 1650R, if I remember correctly. Anyway, it's the 5k, 100W transformer. This strikes a compromise between output power ( more than enough for my purposes) and required drive voltage and output tube peak current.

Tony · 14th February 2006, 03:07 AM

have you read Allan Kimmel's article regarding mu followers? they can really swing a lot of voltage. for instance a 12by7 pentode on top, and a 6cg7 triode at bottom and a supply of 600volts can give you a lot. then you can buffer this with a 6cg7 to set output tube operating point.

downside is you have to have a separate floating supply for the top tube, 12by7 heaters.

13th February 2006, 08:40 PM	#54
Tony diyAudio Member Join Date: May 2003 Location: Palatiw, Pasig City	Andy, thaks a lot. Wrenchome, have you seen david bernings' ut used 2x 12at7's and a 6cg7 tube complement. __________________ http://www.electronicslab.ph/forum/i...?topic=32688.0

14th February 2006, 03:07 AM	#56
Tony diyAudio Member Join Date: May 2003 Location: Palatiw, Pasig City	have you read Allan Kimmel's article regarding mu followers? they can really swing a lot of voltage. for instance a 12by7 pentode on top, and a 6cg7 triode at bottom and a supply of 600volts can give you a lot. then you can buffer this with a 6cg7 to set output tube operating point. downside is you have to have a separate floating supply for the top tube, 12by7 heaters. __________________ http://www.electronicslab.ph/forum/i...?topic=32688.0

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13th February 2006, 05:38 PM	#51
Andy Bartha diyAudio Member Join Date: Sep 2004 Location: Oregon	Wrenchone, This amp is set as pentode with regulated screens. I'm sure it can be set up as triode but the amp is optimized for pentode. So some messaging will be needed to get the best sound for triode operation.

13th February 2006, 07:35 PM	#52
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	From the tube curves for the EL509, a screen driven triode amp will be a very different beast as compared to a pentode implementation, as a lot more voltage drive is required for significant output power, along with some significant screen current. I'm currently wrestling with how to do that while at the same time keeping the number of stages to a minimum.

13th February 2006, 07:44 PM	#53
Andy Bartha diyAudio Member Join Date: Sep 2004 Location: Oregon	Wrenchone, No argument, I was just recommending the output transformer from Electra-Print. For a driver you could consider a mu stage. El-84 over a 6N1P or something like that. Svetlana had a tech tip showing this circuit. They said it could swing something like 350v which would be enough.

14th February 2006, 01:47 AM	#55
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	I want to try and do my own circuit for this amp and not lean too heavily on other people's results. I am very suspicious of using a mu-follwer in this application given the amount of drive voltage needed (at least 150V p-p). I don't see how someone could keep within the peak filament to cathode ratings of the tubes without using separate tubes for top and bottom and isolated filament supplies. At this point I'm thinking of using a pair of 6GF7 vertical oscillator/amplifier dissimilar triodes for amplification and follower duty. I may back this up with an 8CG7 for extra gain if needed. I I'm looking at using a differential pair at the input, maybe with cascode to get more gain, with a 400V regulated supply and about 250V at the plates. I'll be using Hammond iron at the output, as is reasonably inexpensive and readily available - the 1650R, if I remember correctly. Anyway, it's the 5k, 100W transformer. This strikes a compromise between output power ( more than enough for my purposes) and required drive voltage and output tube peak current.

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