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using #47 in p-p
using #47 in p-p
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Old 9th November 2008, 10:39 PM   #1
diesel_tech is offline diesel_tech  United States
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Default using #47 in p-p

Its been awhile since i've posted. But winter is here now.

I've been wanting to use a couple, ore even a quad of #47'S in a simple amp. I've found Gary pimm's, but the end schematic looks way to over complicated. It doesn't have to have perfect frequency respnse. Just has to sound good when using a CD player to drive it. Looking for something simple. Any ideas?
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Old 9th November 2008, 11:33 PM   #2
Eli Duttman is offline Eli Duttman  United States
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Dude,

A look at the type 47 data sheet suggests that "El Cheapo" style circuitry will work.

To keep #47 grid leak resistance low and 12AT7 LTP gain high, insert IRFBC20 source followers that are DC coupled to the 'T7 anodes between the LTP and the "finals".

You choose between self and "fixed" bias.

Don't forget to regulate #47 g2 B+ with a stacked VR150/VR105 setup.
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Old 10th November 2008, 12:06 AM   #3
diesel_tech is offline diesel_tech  United States
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Lamens terms please, i'm new to using solid state stuff, and pretty much all the audio terms.
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Old 10th November 2008, 12:29 AM   #4
Eli Duttman is offline Eli Duttman  United States
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Quote:
Originally posted by diesel_tech
Lamens terms please, i'm new to using solid state stuff, and pretty much all the audio terms.

You have mail.

LTP = long tailed pair, which is a phase splitter derived from a differential gain block.

The IRFBC20 is an enhancement mode MOSFET. As forward bias is necessary, DC coupling to a preceding vacuum anode is very easy. Read MOSFET Follies.

Please notice that the IRFBC20 has a low and stable reverse transfer capacitance. That's the crucial parameter in determining suitability for voltage follower service.
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