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Old 3rd December 2012, 08:46 AM   #261
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Here are some curves, but they are unreliable at higher voltages - the actual bias is about 2v out, like at 220v and 30mA it's nearer -18v than the stated -16v
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Old 3rd December 2012, 09:18 AM   #262
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thanks guys, makes sense now!

regarding the high power cathode resistor, can we wind our own? using this wire?

337 8 Ohm M Precision Resistor Wire Manganin Net 158 9g | eBay

if we could, we could wind it to any resistance we need.

bg
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Old 5th December 2012, 05:49 PM   #263
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If you wind your own, you will get inductance, which may or may not be what you want in that position. The inductance might be too small to effect the operation, but worst case it will reduce the gain as the frequency goes higher, likely substantially out of band. Otoh, how much power do you think is needed? Power resistors are not terribly hard to find or buy.

Btw, I picked up a few of these tubes, thanks to Anatoliy's hearty endorsements!

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Old 5th December 2012, 06:17 PM   #264
Pano is offline Pano  United States
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I have a few of these funny pentodes on the way. Looking forward to playing with them.
Will be using some vintage Hashimoto iron to run the whole thing - PT & OPT. Probably 6SN7 to drive them, as I have some in stock. Need to figure out a filament supply for the 4P1L. Will experiment with other inputs tubes, too.
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Old 5th December 2012, 06:27 PM   #265
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Think 4P1L driving 4P1L - 6SN7s would be a backwards step. Try filament bias as well!
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Old 5th December 2012, 06:44 PM   #266
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HA! That is actually what I had in mind. But thought it was a crazy idea.

Was thinking pentode mode for the inputs, triode mode for the outputs. I can hit the input with about 1.5VRMS max, so need a gain of at least 15x in the input section to drive the outputs.
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Old 5th December 2012, 06:49 PM   #267
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Haven't tried it in pentode as driver, interested in your feedback and your impressions on its sound!
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Old 5th December 2012, 07:07 PM   #268
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Yes, likewise! Pentode in filament bias is a nice possibility.
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Old 5th December 2012, 07:49 PM   #269
Ejam is offline Ejam  Australia
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Default Or Pentode to Pentode with some Schade

You could also try running pentode driver to pentode output with Schade feedback (plate to grid) on the output. Direct coupling is also nice.
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Old 5th December 2012, 08:13 PM   #270
mogliaa is offline mogliaa  United Kingdom
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That is a topology discussed at length by Michel Koster and Revintage in other threads which is really interesting. Lars was after 6p21with Schade feedback driven by a depletion MOSFET. 4p1l MOSFET driving 4p1L in Schade is definitely an option to look for. Greater efficiency out of the 4p1l and minimum components. Again, key question here is about the sound.....
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