[Boatanchors] Line Voltage issues

[Rick Poole WA1RKT]

From: "Robert Spooner" <rls19 at psu.edu>
Sent: Tuesday, January 6, 2015 5:40:37 PM
>>
>> The problem with autotransformers such as the Variac
>> is that they are high enough impedance that you may
>> see inordinate voltage fluctuation with changes in
>> load unless the current rating is high relative to
>> the current draw.

I have a 15-amp variac that I use on the bench for testing and bringing up boat anchors, and I have found that to be the case.  When I set the variac for 110 volts and transmit into a dummy load with the KWM-2, I see a definite dimming of the dial lights, considerably more so than when just plugged into the wall.  I haven't actually measured the voltage drop but it is significant.

>> My favorite solution is to use a filament transformer
>> to buck the higher voltage down to the rated voltage
>> for the equipment.

Have you found that the voltage drop through a bucking transformer, especially near its current-carrying limit, is significantly less than a similarly-sized variac?

Yesterday I bought one of those Rat Shack DMMs that someone here suggested, that will save the maximum and minimum readings, and between last night about this time and now, I set it to store the max and the min and plugged it into the wall.  Over 24 hours' time I saw a stored maximum of 122.9 and minimum of 114.3.  Another DMM was connected at the same time to provide real-time readings, and every time I looked the reading was between 117 and 119, meaning that the 114.3 and the 122.9 were probably momentary excursions.

In receive mode on the KWM-2 powered by a 516F-2 power supply in stock configuration, at 118 V in I measured 6.17 volts at the filaments of several of the tubes.  LV at the power supply measured +320VDC (haven't yet found a good place in the transceiver to measure it) and HV at the top of the RF choke in the HV cage measured +900 VDC (on receive, with no load on the HV).  So, while LV and HV are a little high (they should be nominally +275 and +800), looks like filaments are right where they need to be.

Not real sure I need to do much, here.

Rick WA1RKT