Hi David,
If you want to the meter to read 1500V full scale with a 1.5M series
R you'll need a meter with a 1 milliamp movement.
The 10 R's in series is a bit of an overdo for the multiplier string,
unless that's all you had handy. The dissipation in the R is only 1.5 W
(max. at 1500V) though, unless you have an HV rated R, two or three 2W
parts in series is a good solution.
73 & Top of the wee hours to you,
Marv WC6W
On Sat, 23 Mar 2002 00:02:01 +0000 David & Wendy Dodds
<gm4wll@talisman41.freeserve.co.uk> writes:
> Hi.
>
> I hope you big guns will excuse a really basic novice question?
>
> I've just finished building my first HT PSU. (Very proud of myself.)
> It produces 1150/1350v at 400mA. Not big by the standards of this
> list, but big enough for a 2c39 amp on 23cm.
>
> The beast is working very nicely, with one exception, which is the
> HT voltmeter. It barely reads at all, when the Avo meter is twanging
> off the end-stop! The PSU is based on the N6CA design and I've
> followed his practice of hanging the meter off a string of resistors
> attached to the rectifier output. As I am using a 100mA FSD meter I
> calculated the multiplier resistors as needing to total 1M5, so I
> used 10 2W 150k resistors.
>
> Can anyone tell me if I've fouled up the arithmetic? (we medieval
> history graduates aren't too hot at this theoretical stuff!!)
>
> My thinking was as follows...
>
> R(multiplier) = voltage / I(fsd) - R(meter)
>
> therefore R(multiplier) = 1500v / 100mA - 0.7 Ohms
>
> therefore R(multiplier) = 1M5
>
> Power rating was calculated as follows....
>
> Power rating = I(fsd) squared x R(multiplier)
>
> therefore Power rating = 100mA squared x 1M5
>
> therefore Power rating = 1.5 W
>
> Am I talking nonsense here? The formulae are lifted from the RSGB
> Rad Com handbook, but maybe I'm not using them right....
>
> 73 de David GM4WLL
>
>
> Please reply to:
> gm4wll@talisman41.freeserve.co.uk (Wendy)
> gm4wll@qsl.net (David)
>
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