{Collins} Re: Diode Rectifiers 516F2



What about the trick of putting a 30 to 50 Volt Zener diode* in series with
the center tap lead of the power transformer to ground?  That will very
conveniently subtract the Zener Voltage from the output.  The problem with
the series resistor is that the power supply output Voltage will change
drastically between receive and transmit due to the changing Voltage drop
across the resistor with different current.   This is true whether it is
used on a KWM-2 or a 32S-#.   However, as long as the Zener remains in
conduction AND the power rating is not exceeded, the drop will stay
relatively constant.



73' Charlie k3ICH



*The only problem is finding a Zener of sufficient power rating and Voltage.
I don't think these are still in current production, but the 1N2800 and
1N3300  series (50 watt rating) should work.   If you figure worst case, 50
Volts times a half amp = 25 watts dissipation.  Of course, you could simply
wire 100,  IN4004's in series for about 50 Volts drop assuming 1/2 V drop
across each junction (HI)!



 ----- Original Message ----- 
From: "Rob" <rob@xxxxxxxxx>
To: <levyfiles@xxxxxxx>
Cc: "Collinslist" <collins@xxxxxxxxxxxxx>
Sent: Wednesday, 26 January 2005 9:19 PM
Subject: {Collins} Re: Diode Rectifiers 516F2


> Hi Bill and List
>
> While I agree with most of what you say, I replaced the 5U4 and 5R4 on
> my 516F2 with silicon diodes with the following results. The 800 volt
> supply now measured 980 volts, and the 300 V supply now measured 480
> volts. These were not octal plug in modules, but 1N4004 diodes (two in
> series to provide the necessary PIV rating) soldered to the tube socket
> pins. What the folks are saying, and quite correctly, is that the higher
> voltage exceeds the design voltage for the each of the two supplies, and
> that excess voltage will stress many of the caps, especially on the 300
> volt supply, hence the need for series dropping resistors. If you
> experienced the same increase in voltage that I did, and have had no
> problems for 30 years consider yourself bloody lucky.
>
> What the guys have failed to mention in the discussion to date is the
> effect on dynamic regulation of the supply that the series resistors
> impose. A vacuum tube rectifier does not present a *fixed* series
> resistance to the load. Its resistance changes somewhat  inversely
> proportion to the load, tending to maintain better voltage regulation.
> That is the tube appears as a higher series resistance at lower load
> currents than it does as the load current is increased. The effect of
> putting in a fixed series resistance has a very detrimental effect on
> the dynamic regulation, that is the terminal voltage between the no load
> and full load extremes. Think about the varying voltage drop when
> operating on SSB, and you will see that the plate voltage on the 6146's
> will swing quite a bit more than you would like. This reduces linearity
> of the stage, potentially reducing audio quality, and increasing 3rd and
> 5rd order products.
>
> My solution to the problem was to put a 5U4 and 5R4 valve back in the
> supply. :-)
>
> >Lets start a string.
> >I have been reading all this info on dropping resistors in 516F2 supplies
while reading all the KWS1 stuff.
> >I bought my first used ex MIL KWM2A in 1974. Used it with a 516F2. Bought
diodes for it from Mr. Dahl. Never put in dropping resistors. Still working
today. Changed 3 of the 6u8s for 6EA8's. Not much else went wrong in 30
years. Sent it off to Dennis in 1991 to tweak.
> >
> >So all of a sudden the wise men say to not use diodes without dropping
resistors and furthermore to turn the thing on with a Variac because it was
built to run at 110 not 115/20.
> >
> >Gentlemen. Collins created the first diode mod. Its run on whatever
voltage I ever gave it. Field day, Ranch, City, Country. For 30 years.
> >
> >Sure its getting old. Someday I will replace the caps on the radio and
power supply. But surely they should fail first?
> >
> >Perhaps I am missing something. I ain't a tech or an engineer but I have
been at this tube stuff since 1961 and took my Extra from the FCC on tube
stuff and 20 wpm. I am not a kid and I don't get all the blah blah on Diodes
and Variacs.
> >
> >So I guess I am saying " What? Me Worry?"
> >
> >Please explain in laymen terms your opposite opinions.
> >
> >
> >
>
> >All the best from New Zealand
> >
> >Rob,  ZL1RD
> >
>
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