[AMRadio] Auto transformer to reduce line volts

K9FH k9fh at arrl.net
Sun Nov 29 15:11:48 EST 2015

On 11/29/2015 1:31 PM, CL in NC via AMRadio wrote:
> I know some folks use and auto xfmr to lower their line to the older gear.  Do you split the difference between what
> the transformer gives when in receive and what it loads down to while transmitting? 

Folks might use a variac to lower their line voltage since the line
voltage normally supplied to homes has crept up through the years.
Hopefully most equipment can tolerate a slightly increased line voltage
without resorting to using a variac. But the increased line voltage
might also adversely affect tube life due to the corresponding increase
in filament voltages.  So lower the line voltage to the older standard
of 115 or 117 volts.  You want to prevent excessive filament voltage at
all times so adjust during receive and hope the line voltage is stiff
enough that any voltage drop during transmit is insignificant.

My opinion could be wrong and careless but I don't normally use a variac
in the operation of equipment. It's only used during testing.

> My only auto transformer I use on the 
> bench, but in my catch all loft, I found an 1800 watt Luxtrol incandescent lamp controller that will also do up to  50 40 watt florescent lamps too.
> At first I thought it was a big rheostat, but is actually an auto transformer.  It does say 1800 watts of  regular bulbs, but since it 
> also handles florescents, how do you think it would work feeding ham gear, if at all?

Just make sure that it actually is an autotransformer and not an SCR
controller.  If in doubt, look at waveform on a scope being careful of
isolating the scope chassis from power ground in some way.

Phil - K9FH

More information about the AMRadio mailing list

This page last updated 22 Feb 2018.