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Sweet!

Posted by Paul Joppa (P) on June 21, 2004 at 10:48:35

In Reply to: Simple 84 posted by Gordon Rankin on June 18, 2004 at 10:44:59:

I love the simplicity of a one-tuber "spud" amp. I've often thought that a single EL-84 would be nice, except that it needs a little too much drive. The step-up is a great solution!

I see it is drawn as a pure pentode amp. Looks to me like it could be wired with a switch, triode - ultralinear - pentode. Gordon, any comments on this choice?

The only risk I see is that the 5v winding on the PGP8.1 is rated 1.25 amps, and the 5Y3 draws 2.0 amps. Maybe Mike (once he is back from vacation) can answer how far this winding can be safely "pushed"? I know he is generally conservative in his ratings. If not, the lowest current 5 volt tube I know of is the 5W4 at 1.50 amps. In 6 volt rectifiers there are 0.6 amp tubes, for a total of 2.12 amps from the 6v winding - that's only 6% over the 2A rating.

The other solution would be silicon diodes, which I like but I recognize that not everyone does. In this case, they would raise the voltage quite a bit, perhaps too much. Even the 6X5 has a fairly high perveance and will raise the voltage some.

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