Tubelab SE with a 6BX7 to drive 845s - diyAudio
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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 3rd March 2009, 09:02 PM   #1
rknize is offline rknize  United States
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Default Tubelab SE with a 6BX7 to drive 845s

So I have a box of parts that was filled while inspired by Morgan Jones' push-pull 845 direct-drive ESL amp. I now have a family and a 2-year-old, so such a project is simply out of the question for safety reasons alone, let alone the fact that I will likely never have the time or energy or money to build a set of ESLs.

Anyway, I have a couple of Tubelab SE PCBs. While I wait for transformers for one, I am looking into possibilities of building an 845 SE amp with the other. 45 tubes are getting really expensive and 300Bs are...well...300B-expensive. I have these NOS 6BX7s that I picked-up after reading that book and looking through the TDSL. I think Jones had the right idea that these tubes are a great choice for driving an 845 cheaply. Stick a "PowerDrive" type circuit in-between and it seems like that would rock. The bias adjustments would even let you compensate for imbalance between the two halves reasonably well.

Looking through George's "845SE" pages, it seems like the first FET stage should have no trouble driving a 6BX7. So it should just be a matter of tweaking the final CCS to move the 6BX7 to a better operating point and maybe tweaking the input impedance of the second FET.

It would be sweet to do *something* cool with these "Made in Chian" 845s and it would also look kind of funny seeing those big bottles driven by one little octal tube.

Anyone ever try anything like this?
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