[R-390] R-390A Power Transformer, going SS and turn on surge (was R390A Audio Solution)

Fri Jan 4 10:15:57 EST 2013

Hi Bernie:

Lots going on in that message ;)

I agree with pretty much all you said regarding the inrush limiters.  I 
cannot imagine an application that would be adversely affected thru 
their use---especially an Rx like the 390A.

One thing tho....the relay-based limiters I have used have the relay 
activate to bypass the resistor.  So when it comes on, there is no wait 
for the relay to activate.  the resistor is in place at all times and 
gets bypassed AFTER the waiting time---

But the surge limiters are SOOOO much simpler to use...and especially 
when you typically need to drop a few volts of line voltage anyway.

Nobody that cares about frequency stability would be silly enough to 
expect stability prior to warm-up anyway...most leave them run 24/7 if 
that is their game.  If it isn't stable after warm-up, the inrush 
limiter is not the issue.

FWIW

Curt
KU8L
50+ years in Amateur Radio

On 1/4/2013 7:22 AM, Bernie Doran wrote:
> Hi Ken: The only thing wrong with this idea is that the transformer is 
> still hit with the current inrush when first turned on. IE before the 
> relay pulls in.   I still am amazed that the current inrush limiters 
> are met with any objection. They are simply the best solution, Based 
> on performance, cost, and size.   Perhaps that is the problem, many 
> may think that any design must have esoteric qualities and great cost 
> to be effective.  The only place where time delay circuits  become 
> necessary are those that are turned on and off frequently( the inrush 
> limiters must cool for a minute or so)   and other special circuitry 
> that probably already has time delays built in.
>
> Just try the stupid things and see for your self.  Watch the voltage 
> start low and rise to the applied voltage and I bet you will say, why 
> did I not do this earlier!  Usually takes a second or two depending on 
> the selected limiter.   Properly selected they will stabilize at a 
> voltage drop of about a volt or so in the typical 100 to 200 watt 
> equipment range,  less in high power stuff.   They do get hot, and 
> have to be, to be functional, the cold resistance is many times the 
> hot resistance.  They do not get as hot as many vacuum tubes. However, 
> they should mounted as one would mount any resistor that dissipates a 
> modest amount of power.  Just position them away from the chassis 
> enough  to allow movement of air around them.  The concept that they 
> cause poor voltage regulation based on ambient room temperature also 
> baffles me.  Properly selected as indicated their normal device 
> temperature in the range of a few hundred degrees, enclosed inside a 
> box that does not reach a stable temperature for hours, you are going 
> to tell me that a small change in room temperature is going to have an 
> discernable impact?
>
> Now if you select an inrush limiter designed for a several ampere load 
> and set up a test feeding a load of say 250  millamperes and stand 
> there with a fan turned on and off, the load voltage will jump all 
> over the chart!! Guess what, you just discovered a thermister!  This 
> is a case where "safety factor"  does not apply, they must operate at 
> their design range of current flow.   For most equipment one can 
> simply use the rated watts and voltage to calculate the amperes, for 
> those that are fussy use a power factor meter or guess at a power 
> factor of .8 to .9.   For a transmitter that uses a common transformer 
> for all power there will be a change in line current between standby 
> and transmit.  Likely not much more that two to one, should not be a 
> problem, just select the inrush limiter that has a maximum rating for 
> the current drawn on transmit.   They are designed for a small range 
> of current that and selection should not be too difficult.  If there 
> is a separate plate transformer then use one for the plate transformer 
> primary and another in the B+/ filament transformer.
>
> These discussions rather remind me of the concerns about all sorts of 
> exotic replacements for the non off the shelf current regulator tube 
> for the two oscillators.  Just remove the regulator, save it, place a 
> jumper in the socket, and replace both oscillator tubes with their 
> twelve volt equivalent. Then when you sell it, change it back and 
> extol the virtue of this fantastic design that even regulated the 
> filament power!  Never mention that it was designed that way to 
> operate from sources of power with poor regulation.
>
> How do these changes impact performance? My 390A  has  all of these 
> modest changes plus (horrors) even a series ten watt dropping resistor 
> to operate the tubes at their minimum rated filament voltage,and a MOV 
> following the dropping resistor. I have turned on my gear in the 
> garage on days that are far too cold for me to stay there very long, 
> Does it drift? certainly it drifts, usable within a minute,and for my 
> purposes fully stable enough for me to operate in the time it takes 
> for the transmitter warm up and look around the band/bands.   I do 
> keep a light on in the room during cold weather when there is a chance 
> of condensation under warming conditions. Now suppose you say, well I 
> demand  that it is totally stable immediately and able to read the 
> frequency to one cycle because I operate only SSB  on one exact 
> channel for my round table, also my line current jumps from ten ampers 
> to seventy ampers when I yell at the parallel 3CX5000s.  Then I would 
> say you might have several issues, and perhaps stick with Jap stuff, 
> and hopefully on the high end of 80 and away from me.
>
> This is way too long and I apologize for boring any one to death.  I 
> will not do it again.
>
> I have never done this before, but I will say that this is based on my 
> opinion as an amateur with nearly 60 years of experience (1954) and 
> also my Professional opinion.    Bernie Doran    P.E.   W8RPW
>
> ----- Original Message ----- From: "Ken Harpur" <igloo99nz at yahoo.co.nz>
> To: "R-390 at mailman.qth.net" <r-390 at mailman.qth.net>
> Sent: Thursday, January 03, 2013 10:00 PM
> Subject: [R-390] R-390A Power Transformer,going SS and turn on surge 
> (was R390A Audio Solution)
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