[Amps] Utilization of old TV transformer

[Manfred Mornhinweg]

Vic,

> So the primary is good for 313 VA continuous.

Yes - but the secondary isn't!

> I was doubling that to allow for the duty cycle. I agree that this is
>  skating on the edge (standard ham practice, right?)

Actually it's quite a bit over the edge! You are forgetting that 
doubling the current QUADRUPLES the power loss in the windings! That's 
OK only if you reduce the duty cycle to 25% maximum, and also make the 
cycles short enough to keep the wire from overheating during one cycle.

I would say, pushing a transformer to twice its continuous current
rating is perfectly OK for the PEP level of a SSB amplifier, as long as
not too much voice processing is used. But definitely not OK for CW!

> However... the 813's deserve better. So I think I am going to look 
> around for a transformer that I can get 2400 - 2800 V at 350 - 400 mA
> from.

That's MUCH better!

About ten years ago I wound one like that. It also has the 10V filament 
winding, and windings for screen an bias supplies. And I never used it, 
because while I was building the amp, I got the chance to buy the 
National Radio amp for almost no cost, and that made me shelf the 813 
amp project.

But shipping that beast to you would certainly be more expensive than 
getting one locally!

Manfred.

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