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Svetlana 1st September 2006 12:16 AM

Loftin-White coupling Questions
he uses a Loftin-White to couple the 6sl7 to the 845.

Is there any info on the theory of this?

I want to try it, (6sl7/6sn7 > 211) but not sure how the bias, supply voltages, and cathode conditions operate.

It seems using a 6c45 is a popular choice to drive a 211.


States that a 6c45 with a plate of 160, will drive the grid of a 211 B+ @ 1.25kVA, into "soft A2"

What voltage swing will the 6c45 present to the grid of the 211?

With the plate of the 211 at 1.25kva, a bias voltage that swings the grid positive using a 6c45@160V will exceed the 211's dispersion rating?

bear 5th September 2006 01:08 AM

I dunno what others like, but I want my 845s and 211s driven in A2.

The guy with the wierd pinkish purple pages does not show a least not one that I saw - reading his text quickly wasn't terribly illuminating, he says something about using an 845 as a driver? Makes little sense to me actually. If you find the schematic somewhere there, post the page link? The part that said schematic shows a block diagram and power supplies... or maybe I missed it?

The other guy uses a "parafeed" driver to run the output tube in A1. Not my fav. Parafeed is fun, and good in the right circumstances too.

Guess these folks put a lot of thought and time and effort into their building. But in the end the amp is going to depend on the output stage and its performance, all other parts being fairly equal (they're not, of course).

Of the ways to build an amp, these are two? :D

_-_-bear :Pawprint:

Edit: sorry that is a schematic... oog.

Two parafed stages... why the extra 845? Tryin to swing that grid!

The advantage to the parafeed idea is that you get the DC off the primary winding... so that makes good sense when you are driving a transformer...

...thinking out loud - can't recall is the gain of a grid driven 845 only 2?? does it need 750volts of swing on the grid to drive it to full A1 output? Hmmm... maybe I should pull out the tube book and check.

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