What is wrong with an NTC resistor such as a CL40? I put two (one in each 120V primary) of an SB-200 and stopped the lights dimming when the amp was switched on.
If sized right for the application, these devices are great for infrequent use every ten minutes or so such as turning on a linear amp. If the application is a big AM setup where we PTT the B+ by switching the AC primary voltage, then the NTC varistor is a bad choice since the current surge reduction will be limited only for the first time we key the transmitter. These devices might take several minutes too cool off when the transmitter is unkeyed.
These NTC varistors will drop some voltage even when hot. Depending on the application, this drop might matter since the B+ will be lower.
I looked again at the Harbachelelectronics, and they sell several different step-start relay kits. They look simple in design without any IC chips to fail. The consequence of using these however with fast break-in conversation is that the first 1/2 second or so of the transmission will be at reduced power output.
So what does the group think of the options:
1.) relay or switch, and just hit it clunk-groan and all
2.) Step-Start with 1/2 second delay at reduced B+
3.) Use a NTC thermistor
4.) Solid State relay (zero crossing type)* so we hit the power every time without the occasional groan
5.) Use full time B+ like a linear and switch the HV with PTT using a vacuum relay
6.) Use full time B+ like a linear and switch RF amplifier with grid blocked keying
* will likely need resistive load across transformer primary to maintain triac of scr conduction over full line cycle. This could be a incandescent lamp (HV ON).
Maybe we can look at the pros and cons of each approach.
73,
Jim
WD5JKO