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Re: [Amps] Options

To: amps@contesting.com
Subject: Re: [Amps] Options
From: Steve Thompson <g8gsq@eltac.co.uk>
Date: Sun, 06 Aug 2006 08:27:55 +0100
List-post: <mailto:amps@contesting.com>

Martin Sole wrote:
> Start with an assumption.
> You have a quantity, i.e. more than 10, Eimac 8930's (4CX350R some say) 
> with bases and teflon chimneys. Tubes are unknown condition but were 
> removed from service a couple of years ago as working. You have a 
> quantity of transformers marked 1752 volts rms 275 madc, a similar 
> quantity of oil filled capacitors rated 5uF 3000 volt and assorted other 
> componentry, non tank circuit.
> 
> Question.
> What do YOU think might be the most efficient way of utilising this 
> hardware assuming the goal is some minimally specified HF band amp (80 
> through 10 metres).
What's minimal - modest power or no frills, or?
What are you wanting out of it - a simple amp for minimum effort or some 
fun experimenting?

If it's the former, I think there's incompatibility in the hardware you 
have. The transformers will give you 2.2-2.4kVish, which will work the 
valves in the region where you need comprehensive protection etc. Where 
you have the quantity, I'd put extra in parallel and run them at much 
lower voltage, say 1500V, and all the headaches go away.

As a gross generalisation valves are cheap, transformers expensive, so 
parallel up the transformers (use a separate bridge on each and common 
the bridge outputs) to get the power you want, then choose valve(s) to 
suit. A pair of GI7 triodes will cost next to nothing and give you 800W out.

Steve
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