>In message <19980314202033.AAA7609@[205.231.11.91]>, Rich Measures
><measures@vc.net> writes
>>The circuit shown in Figure 1 at:
>>www.vcnet.com/measures
>>is simple, uses a pair of inrush resistors so that it works on 120v and
>>240v, and can be powered by the AL-80's 12vdc (?) supply. The timing
>>element is the hv supply filter capacitors. When the caps. are 2/3
>>charged, the relay closes. For an AL-80 a pair of 7w c. 25 ohm resistors
>>should work satisfactorily.
>>later, Jack
>>
>>cheers
>>Rich...
>
>You might consider using current limiting resistors with a higher
>resistance and power rating, especially where you have a separate HV
>transformer.
The resistors w-rating is chosen according to the size of the amplifier.
25 ohmers limit the inrush current to roughly less than 8A.
> If there is a fault which draws high primary current and
>stops the HV output rising to the value that shorts out the resistors,
>they sit there with most of your line voltage across them until they go
>bang.
That is the idea. The resistors act as fuses in the event of a major
circuit fault. If all's well, the 7w resistors barely get warm during the
c. 1 second step-start.
>I guess it's more difficult with a single transformer as you need
>to let the auxilliary supplies build up to operate the relay.
>
- Two or more transformers act like a single transformer when the
primaries are in parallel.
>Having suffered once, I now use a fixed timer which gives a few seconds
>delay - if there's a fault then the line fuse blows.
>
A fixed timer changes only the capital investment.
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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