Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: xcortes on June 29, 2013, 02:31:25 PM
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Looking at the WE 421A datasheet it seems that a plate follower preamp could be built with a plate resistance of less than 400 ohms at somewhere around 40 to 60 mA. The crack ps delivers up to 140mA at 170 v so instead of the 12au7 an active shunt regulator could be used for both channels, maybe even one per channel. It looks like there's enough room for active shunt reg and c4s loading.
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80v rp, 60mA and -8v bias look perfect to allow extra voltage and current for regulation and c4s. I could dump around 15mA through each section of the 12au7
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At that voltage, could you get away with a choke-input PSU filter?
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Yes, we did that. Used a pair of 7233s. Bass was great, but the highs still had an edge which was removed by using the 300B.
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I have an unused crack and a WE 421A. So I'll give it a shot with the soeedball boards.
Paul, did you skip or maintain the 12au7? I'm planning on skipping it.
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The 9 pin socket was maintained to provide the shunt regulator for the preamp tubes. I think a 5687 was used, but there are other choices.
With the plate follower, you won't need equal regulator current.
If you want to try whacky things with the Crack chassis and parts, you can always e-mail me ;)
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Yeah we got a whole bunch of PB's frankencracks around here.
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Thanks guys. I'm so impressed with the Beepre and having the crack lying around it's a no brainer.
PB: you will get mail!