On Apr 12, 2006, at 9:42 AM, Rich wrote:
> Good day gentlemen, I am putting together a small amp with an old tube
> from my junk box trying to learn as I go. I built a large power supply
> last year for a 4-1000 but I am a little cautious of 5000v my first
> time
> around so I will start small with a 40M monobander at lower voltage.
> I am working on the power supply now and just bought a relay for the
> soft start. The input will be 240v both side switched with two SS
> relays. When I install the soft start do I need to put a resistor on
> both sides of the hot line or is one side sufficient ?
> The main question today is the soft start relay, 25A@240VAC P&B PR7DYI,
> plenty good to the low power I will be running. The 24vdc coil is 287
> ohms, it will be on the 120VAC line with a 1N5408 in line. What size
> resistor and cap should I start playing with??
If you are planning on using a half-wave rectifier and C filter running
direct off of 120vac to power the step-start relay, you will start with
c. 150vdc under load, so you need to drop roughly 130v with a series R
in order to set the relay step point at c. 2/3 of normal HV. My guess
is that this resistor will turn out to be c. 1500-ohms / 10w.
Another method of powering the relay coil is to run a FWD
rectifier-filter from the filament winding. This should produce about
20vdc, which should be enough DC to pull in a 24v relay. One 10 to 20
ohm, 10w resistor in each side of the 240v mains should do the job.
> Rich , kd0zz
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>
Rich Measures, 805.386.3734, AG6K, www.somis.org
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