Soft start plans needed for Johnson Viking 500

[N2IDU]

I need to know how to hook up a soft start to my JV500 transmitter. I have on hand many high wattage low value resistors and relays to do this project. I have never done a soft start so I would need to know very specifically how to accomplish this. Anyone out there have an existing working circuit for a JV500 that they could share with me?
Thanks,
Peter  N2IDU  "Old Shincracker, Vt.

[WA1GFZ]

Take a 115 VAC coil voltage relay and wire it across the power transformer primary 115 VAC winding.
Wire a power resistor in series with the AC lead hot (2 if you are running 240 one on each hot lead. use 10 to 25 ohms at least 25 watt rating) Now wire the relay contacts (you need 2 poles if 240 VAC) so the resistor(s) are shorted out when the relay pulls in.
Power Turn on sends current though the resisitor(s) slowly increasing the primary voltage until the relay has enough voltage to pull in and short out the current limiting resistors.  Play with the resistor values to get the delay you want. 1 second is plenty slow enough.
KISS

[KC2ZFA]

I second GFZ's KISS method.

When I was building my two 1250V supplies (each with a 10H choke and 90 uF of capacitance) I wanted to first determine what the inrush current was by blowing fuses. I determined it was between 7 and 9 amps (blew a bunch of fuses till I got to 10 amps which didn't blow but the supplies shook on start-up). So I put in two KISSes with a large 5 ohm resistor and now the supplies start with a 4 amp fuse and, significantly, no earthquake.

[K5UJ]

There was an article about soft start for the 500 in ER a number of years ago.  I'm only an armchair non-expert.  To  me the problem with relays and resistors is that while they are FB for amps where the B+ is on all the time after you switch the amp on the first time during an operating session, AM rigs key the high and medium v. on each transmission by switching the transformer primary 60 cycle current on and off so the relay/resistor method may not work as well? 

Anyway, the ER article said that 500 inrush (as with any rig) depended on where you hit the line service v. cycle the instant you keyed the rig.  The author recommended using thermistors in series with the primary supply lines.   The two probs I have with that are A. the thermistors get real hot (but that can be dealt with by placing them in locations away from things) and B. I think they have to cool down in order to do their thermistor thing on the next transmit cycle i.e. they are only good if you go to receive for long enough for them to cool down.  Maybe they cool down real fast though.   They seem to be appealing as passive non-mechanical devices.

I have been experimenting with thermistors in small things like audio amps and transformerless 5 tube broadcast receivers where the cold filaments get a big current surge.  I've metered the line current and they do seem to help.

[WQ9E]

I installed inrush limiters in mine as per the ER article and I have been pleased with the results.  Mine has been operating this way for about 5 years now.

Many Viking 500s, including mine, had a problem with the "mechanical delay" relay that controls the external antenna relay and is supposed to have a slow release to avoid hot switching the antenna.  The delay disappears over time so you end up with the antenna relay opening too soon on the transition to receive and it will either fire across the protective gap (if properly adjusted) or will jump across the much maligned HV connectors if the gap is open too wide.

I installed a small (10 uf as I recall) capacitor across the relay coil along with an isolating diode to provide a small delay on break and had no further problems with the gap firing.  I have the original power supply connectors which are fully capable of withstanding the normal voltages without arcing to ground and mine have never flashed over.  If the gap is open too wide AND you replace the connectors with some capable of higher voltage then the HV pulse from hot switching will find another, likely more expensive, way of going to ground.  The Viking 500 instructions exacerbate this problem by instructing you to open the protective gap further if nuisance arcing occurs.

If you install a capacitor across this relay, carefully observe polarity.  As I recall this relay is fed by a negative polarity DC supply.

[N2IDU]

Ok, Thanks for your input. Some good ideas to consider for sure.

[KA2QFX]

BTW. One of the nice features of Frank's method is if there's a short in the rig (rectifiers,filter caps...) the drop across the soft start resistors will keep the relay open indefinitely. That beats the R/C time delay method hands down.  You may let the smoke out of the soft start resistors but that sure beats letting it out of something else made of unobtainium.