[R-390] RE: 390A relay problems

[Bob Young]

Hi Don,

They don't run real hot and are well ventilated and I'm not drawing anywhere 
near 2.5 amps with them (which may be the reason they are not that hot, but 
will keep that in mind). I think maybe the selenium rectifier may be partly 
to blame in the 390A as someone pointed out (you?) as the relay in my 390 
works fine with them, my 390A is is the one that makes the noise. I think 
the 6 volt drop is a good idea as these were designed to run on 115 VAC 
anyway, the house current here is normally about 121 VAC which makes it just 
about right.
And yes that is the correct blurb for the one's I have. thanks,

Bob KB1OKL

From: 2002tii <bmw2002tii at nerdshack.com>
To: r-390 at mailman.qth.net
Subject: Re: [R-390] RE: 390A relay problems
Sent: Saturday, September 29, 2007 4:00 PM
Bob wrote:

	 	Perhaps it is too big?, it's a 300 watt limiter. I also notice if I 
switch past standby and go right to AGC, it immediately pulls right in,

It is certainly too big for a 390 on standby.  I found the following on the 
web, which I think is about the particular unit you have:

"The instant the equipment is turned on, the internal meter will show a drop 
to about 60 VAC, and then it will rise over the next ten seconds to a value 
near 100 VAC. This rise will continue for about two minutes where the load 
voltage will level off and hold for as long as the equipment is turned on. 
The drop in load voltage at turn-on from 120 volts to 60 volts represents 
substantial inrush current limiting. This slow built-up to operating voltage 
is what protects your equipment from possible damage. For example, power 
supply filter capacitors in a power supply are present nearly a short 
circuit to load current when they are discharged. Vacuum tube filaments will 
last a lot longer if they are not subject to full voltage when they are 
cold.  After the initial warm-up period, the limiter will have a constant 
voltage drop of about 6 VAC. This voltage drop means your vintage equipment 
will operate at the line voltage it was originally designed for, which was 
about 115 VAC."

This is a very slow ramp, not like the typical inrush current limiter, which 
ramps up over a fraction of a second.  It also indicates a steady 6 volt 
drop, much more than the usual inrush limiter.  At the rated 2.5 A, this 
thing would be dissipating 15 W inside its plastic housing!  Can you say, 
"fire hazard"?  I don't think this particular device is likely the best 
approach to operating a 390.

Best regards,

Don