Re: Power supply adjustments

Bob McGraw - K4TAX

Any of the Astron supplies and likely others should be adjusted {usually internally} to 14.5 volts at the supply terminals with NO load or nothing connected to the supply.     Mine are SS-30M supplies and one RM-30 supply.   

If you have SS-30M supplies, the voltage adjust pot is on the front right of the PC board as viewed from the front of the supply.   The pot that is hanging in the air behind the Volt meter is for the meter calibration.   Likewise, the pot that is hanging in the air behind the Amp meter is for the calibration of that meter.

Then, with the radio in CW mode, transmit at 100 watts, key closed, you should see 13.5 to 14.0 volts on the K3/K3S voltage display.    If your voltage indicated is lower than this, check the voltage at the supply to confirm it is not dropping under load.  If it is not, then suspect the connections on the power cables from the supply to the radio.    If you use a power distribution strip, I suggest not connecting the radio to the power strip but connect the radio direct to the power supply.   Every added connection and plug in the DC path does adds resistance and thus voltage drop.   E = I x R   Therefore 20 amps and 0.05 ohms equals 1 volt drop between the supply and the radio.   That 0.5 ohms is the total combined resistance of the DC Pos and the DC Neg and the fuse and any other connections in the path.

PLEASE read the article in QST, November 2019, by Rob Sherwood.  "It's Time to Clean Up our Transmitters"   pp 38 -41


Bob, K4TAX

On 11/7/2019 1:37 PM, Edward McCann wrote:

Which 30 Amp Astron power supply?

Let us know the results!



On Nov 7, 2019, at 10:22 AM, Michael Mickelson <mickelson@...> wrote:

Bob, thanks for that information.  I have two of the 30Amp Astron supplies and will make an adjustment to a higher setting.  The discussion on the effects of supply voltage on the K3/K3S tranSmitter performance has been very inStructive.

Thanks to all who contributed.  Mike  KD8DZ

On Wed, Nov 6, 2019 at 5:18 PM Bob McGraw - K4TAX <rmcgraw@...> wrote:
Why not get Alexa to adjust the voltage for you?   "Alexa, turn the
supply on and set the voltage for 14.5."

The supplies are usually in the category of the "set and forget" type.  
Thus the caution of "no user serviceable parts inside".

I adjusted one of mine this afternoon.  I put it on the desk, removed
the 4 screws holding then cover, plugged in the cord and turned the
supply on.   I picked up my light in one hand and my plastic adjustment
tool in the other {you do have and use a plastic adjustment tool don't
you?} and made the adjustment. Nowhere at any time did my hands or
fingers come close to any voltage.    I did put my Fluke DMV on the
output terminals first to monitor the voltage.  At 14.49 indicated,  I
stopped.   Turned the supply off, put the cover on and secured it with
the 4 screws.


Bob, K4TAX

On 11/6/2019 3:54 PM, Rick Bates, NK7I wrote:
> And for some stupid reason, when they could have put that pot on the
> underside of the circuit board (which ends up on the top) for simpler
> access, they didn't.  So you're reaching in around open hot high
> voltage OR turning it on/off a lot of times to get it set right.  Plan
> B could have been to put the pot on the edge or board flush with a
> hole for a plastic tool to access...
> I maintain that if the design engineers (of ANY field) EVER had to
> work on, fix, adjust their product, the design would be far different
> and techs would bless them instead of using 'adult language'
> curses...  ;-)
> I hold that Elecraft 'gets' this, their designs are modular and except
> cable routing and some panel connecting, is boringly simple.
> Rick NK7I
> On 11/6/2019 10:32 AM, Rob Sherwood wrote:
>> The Astron power supplies I own have an internal pot to set the
>> voltage. I would adjust it with nothing connected.  The can likely go
>> over 16 volts. I have 3 RS-35Ms, but have never used a 50. For some
>> reason removing the top covers are a pain.  Rob, NC0B

Michael Mickelson
J. Reid Anderson Professor of Physics and Astronomy, emeritus
Denison University
740-587-0687 H
740-644-1238 M

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