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In Reply to: RE: What tubes to use with this Interstage Transformers? posted by Tre' on August 24, 2016 at 18:11:06
So, the CMiller and the r at the Output tube is dependent upon the Frequency and it will make the frequency roll off somewhat problematic. It's also true the impedance from the output tube got reflected to the plate of the driver tube but as long as it's not very high, I don't see how it poses a problem.
In the case of the 801A, the data sheet suggest the 425V B+ at 18mA plate current will require about 10K ohm load resistance so if I load it with 10K-15K Primary of the IT, I think it should work fine. Would you otherwise thinking it will not work?
I just need to make sure the Secondary of the IT is connected to the overall Impedance of 160K or more if possible. Thus, the quest for the suitable output tube begins.
1:4 IT isn't a problem to drive the output tubes. I just need to find the right tubes. Tango has NC14 with 1+1:1+1 and you can wire it as (0.5:2) which is 1:4. NC14 have lower Primary load impedance though.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Follow Ups:
"I just need to make sure the Secondary of the IT is connected to the overall Impedance of 160K or more if possible. Thus, the quest for the suitable output tube begins."Using a 1:16 IT you will need an output tube with a very low Miller capacitance to meet that goal......like a pentode....I was assuming that because you are using a direct heated driver tube that you would be looking for a direct heated output tube.
Direct heated output tubes have very high Miller capacitances.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/28/16
Thank you Tre! I appreciate your valuable input and I am now looking closely at the values for Grid to Plate C of the output tubes in my quest.
You are right that I am only looking to drive DHT output with DHT driver tube.
Thanks,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
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