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Old 29th March 2012, 09:52 PM   #21
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Join Date: May 2007
Greetings from FixitLand!

Re the EF80 (AKA 6BX6)...looks rather like a 6AU6 on a B9A base. Thanks for the info; I'd been thinking of trying a pair of 6AU6s out as a flea-power amp just for laughs, and this makes it seem more likely to actually work.

Take care,
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J. E. Knox "The Victor Freak"
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Old 30th March 2012, 09:54 AM   #22
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Has anyone tried ECC99 as a power triode? http://www.jj-electronic.sk/pdf/ECC99.pdf

looks like it'd be good in something like this.
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Old 30th March 2012, 01:15 PM   #23
MelB is offline MelB  Canada
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Dude, with a 290AX you are going to end up with well over 400 volts on that 12au7.

That puts you right "off the chart" The curves I can find only go to 375v.

I'd start with -30 volts as a bias. You'd want 6K PER cathode. I'd go with separate cathode resistors as well. You will be totally maxing these tubes out. Start with a high cathode resistance and work your way down. That would be my approach.

Also this will require a lot of dicking around. Put a bleeder resistor on there for starters so you don't kill yourself.
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Old 30th March 2012, 01:33 PM   #24
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Try a 12BH7 instead of the 12AU7.
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Old 30th March 2012, 11:48 PM   #25
shonen is offline shonen  United States
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Hey dude... thanks, I am planning to step it down to around 300V somehow. Method not yet decided. The 125A OT arrived and it is teeeeeny!




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Old 31st March 2012, 03:32 AM   #26
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If you use a choke for filtering start off with it before the first cap. Lower voltage and better regulation ... if you think that's a good thing. Try running both Pi and choke input filters with that tranny in the Duncan supply modeler.
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Old 31st March 2012, 11:46 PM   #27
shonen is offline shonen  United States
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That's what I was wondering. An isolated choke vs taking power off the preamp rail after the first cap / resistor... thanks. gonna try to get a model working so I can kill myself virtually..

btw, ever use SPICE? i'm on linux primarily and have gEDA installed. have a feeling this will kill an entire day to get working as a tube amp simulator.

Last edited by shonen; 31st March 2012 at 11:52 PM.
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Old 1st April 2012, 02:47 AM   #28
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If you don't have a choke in there already a resistor before the cap will do the job. It will be a lot smaller than a dropping resistor - even 100R will probably be enough.
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