Tube DIY Asylum: Re: Looking for a GOOD 211 / VT4-C Schematic by Paul Barker Do It Yourself (DIY) paradise for tube and SET project builders.

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Posted by Paul Barker (A ) on July 19, 2003 at 06:02:25

In Reply to: Re: Looking for a GOOD 211 / VT4-C Schematic posted by Super_BQ on July 19, 2003 at 02:19:59:

Balanced? Main benefit is in low level stages, once you've amplified signal to 2vrms maybe the benefits do nopt outweight the added complexity. That said Steve Bench has an 845 circuit which is push pull up to the 845 and then single ended. This could be adapted to retain your balanced topology right up to the 211, but it would be a lot easier to stay single ended.

2vrms is quite good, 2.828v peak.

I was wrong about power out. It takes greater voltage swing than I thought. That's working with the 212 for you, it's clouded my judgement. Take the standard high voltage operating point of 1250v 60 mA into your 10k load. You can develop 13 watts from a grid drive of 60v peak (theoretical maximum just under 20 watts from 75v peak drive)

To develop 60 volts from 2.828v requires a voltage gain of 21. It's no use saying good the 6sn7 idea will get us there, because you will necver develop a voltage gain equal to the mu of the valve, and not many 6sn7's you test will actually have a mu of 20. I think you must select a valve that has a little more gain in the first place.

It's now becoming clear why the 6c45pe is populare for this application but it's not the only option, and it isn't pressed into service without some care in application (parasitic oscilation around the 6c45pe can make the resultant amp sound quite solid state like).

That said the circuits already exist and hand it to you on a plate. Buiuld it on a bread board and see how you like the sound, then try something else, to see if it can be improved upon.

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