>From: Steve Thompson <g8gsq@eltac.co.uk>
>To: amps@contesting.com
>Subject: Re: [Amps] Options
>Date: Sun, 06 Aug 2006 08:27:55 +0100
>
>
>
>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.
>
One of the problems with trying to build a multi-tube amp using tubes of
unknown and variable characteristics is keeping the tubes balanced. To build
an effective multi-tube amp would really require making a jig to test and
grade each tube. (One use for a socket, transformer and capacitor).
As an experiment, but not necessarily an efficient use of hardware, you
could built a number of a stand-alone self contained low power amps and
combine the outputs. The combining network could be quite an interesting
exercise.
Regards
David G4FTC
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