At 19:58 2000-06-25 , Larry, W7IUV wrote:
>I have shared your concern for many years, but the results of a recent
>project have altered that opinion somewhat.
>
>In this ham shack I have a rule: There will be NO high voltage present
>anywhere during receive mode. Period. Non-negotiable. End of discussion.
Larry, I see absolutely no reason for this.
It will only make things more complicated, and serves no purpose. 220V AC
(Europe) is just as lethal as HV and we find that in all power supplies in
the shack . Why not switch off the 220V AC too during receive mode.. ? :-)
The way to preserve safety is to use good cables, good connectors and to
think twice before sticking your fingers into ANY equipment.
Sounds to me like you make this statement to stick out from the rest of the
crowd by using more hardware and timing.. or is there another reason behind
your non negotiable decision ? Maybe you put your hand into the amp to pad
the tube for doing well after each tx period.. :-))
Ciao,
Peter SM2CEW
>This is relatively easy to achieve with choke input high voltage supplies,
>but normally precludes the use of cap input filters. In order to use a cap
>filter in the latest supply (for the YC156), I had to get creative to limit
>inrush current and still ramp up in a reasonable period of time.
>
>The final circuit consists of a double pole mercury relay in the 220 mains
>line with two 5 ohm 50 watt resistors in series with one side of the 220.
>The first resistor has a SSR (45 amp, zero crossing) across it with a time
>delay of approximately 50 mS. (about three line cycles) The second resistor
>has a duplicate SSR with time delay of 100 mS. Approximately 6 line cycles
>after the "TX" line is enabled, full mains voltage is applied to the
>transformer primary. The fluorescent lights in the shack dim less than when
>the home air conditioning unit kicks on.
>
>To accomplish "accelerated life testing" of this circuit, I simply tuned up
>to full power, adjusted the keyer speed to 5 wpm, set the FT1000D for QSK
>and started sending code. The supply has no trouble following the slow
>speed code. Of course, one must compensate for the slight delay in amp
>output, but it's not hard to do that. The supply has been used for several
>contests and a lot of DX pile-ups with no problems other than what appeared
>to be a single random diode failure.
>
>I still don't trust the SSR's enough to eliminate the mechanical relays
>entirely, but for surge control they seem to be an excellent choice.
>
>Just my opinion. Others may vary.
>
>73,
>
>Larry - W7IUV
>
>
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