Question on driving power....

[rsumperl]

Greetings,
   Been way too long since I've been out of school, so if my modulator tubes in Class B need 3.4 watts to drive them, how much power should the driver be able to provide? I don't remember what typical loss is through a transformer.

Thanks,
 Ray

[k4kyv]

To be on the safe side, I would recommend driver capability at least double that. A pair of 6B4's or 2A3's, class AB1, with cathode bias would do nicely.  Of course, you would need a good driver transformer.  A solid state driver or direct coupled cathode follower might be easier to build with obtainable components.

[rsumperl]

So, if I need 3.4 watts, will a driver supplying 6 watts be adequate?

Thanks,
 Ray

[k4kyv]

That would probably do it, but you need a driver transformer unless you go to something like direct coupled cathode follower.
A pushpull driver would be preferable to something single ended.

[rsumperl]

Why would a push-pull driver circuit be a better choice?

Thanks,
 Ray

[KM1H]

If the price of those tubes scares you off consider the 6N7 metal version which isnt of much interest to the audiophools. A pair of 12B4's or a pair of 12BH7's  with sections in parallel could also be used but the cost is jumping due to those audiophools.

If perfection isnt of interest PP 6AQ5's are quite respectable.

Carl
KM1H

[rsumperl]

Actually, I was considering a single 6Y6 as with 200v on the plate will give me 6 watts. I also looked at some metal 6L6's in P-P, however they'll eat some 140ma @ 250v.
Also looking at 6V6 P-P or 6BQ5 P-P

[wb6iyh]

If the price of those tubes scares you off consider the 6N7 metal version which isnt of much interest to the audiophools. A pair of 12B4's or a pair of 12BH7's  with sections in parallel could also be used but the cost is jumping due to those audiophools.

If perfection isnt of interest PP 6AQ5's are quite respectable.

Another choice is the 6fm7 which has two dissimilar triodes in one envelope.

The low mu, higher current unit has lower Rp than a 12B4, and the high mu trode is similar to a 6j5.

Two of them can be used to build a phase inverter and a push-pull driver with only two tubes.

http://scottbecker.net/tube/sheets/123/6/6FM7.pdf

I have a schematic I got from an audio site showing a schematic for this.

And they are cheap.

[rsumperl]

Greetings,
  If you're able to post the schematic or link, that would be great!

Thanks,
 Ray

[wb6iyh]

I didn't post the schematic because I wasn't sure of the copyright issue.

And I couldn't find the link.

Well, here it is.

http://www.sky.sannet.ne.jp/tossi/data/lib/9306_2.html

As you can see it's Japanese -- that explains why I had trouble finding it with google.

(When I first posted this message I had the wrong link. It's right now)

[wb6iyh]

Here is another schematic using the 6EM7 which is essentially the same tube, but the octal version.

http://www.sky.sannet.ne.jp/tossi/6em7/6em7pp.BMP

(When I first posted the previous message I had the wrong link. Fixed it now).