[Hammarlund] : Tube shields and heat

[Richard Knoppow]

----- Original Message ----- 
From: "Bob Camp" <kb8tq at n1k.org>
To: "Guido Santacana" <gsantacanav at gmail.com>
Cc: "Hammarlund QTH LIST" <hammarlund at mailman.qth.net>
Sent: Monday, September 29, 2014 4:14 AM
Subject: Re: [Hammarlund] : Tube shields and heat


Hi

Most of these radios were designed in an era of 105 to 110V 
AC line voltage. We still call it 110 today, even though it 
probably is 118 to 124V. For some parts power does indeed 
follow voltage squared. That can be good or bad depending on 
what you are up against. A simple autotransformer based on a 
12V filament transformer will fix the problem without a lot 
of crazy effort.

Bob

     "Standard" power voltage in the USA seems to have begun 
at around 110 volts and gone up slowly. Around 1940 it was 
115 or 117 volts, later it became 120 volts. I monitored 
line voltage here for a while during a recent heat wave. It 
varied from as low as 108 volts to as high as 124 volts 
depending on time of day (how many people had air 
conditioners going etc). During light load times it crawls 
up to around 122 to `124 volts.  This is probably partly 
house wiring but was measured on a circuit with low demand, 
I think the variation was mostly from LADWP.
     The reason for higher supply voltages is simply to make 
up for the expected loss in the transmission lines. Using 
larger wire and higher capacity transformers would allow 
lower supply voltages but is expensive.
    A simple bucking transformer can compensate for high 
line voltage but where there is a lot of variation, 
especially where voltage goes low at times, a regulator of 
some sort is in order. The simplest is a Sola type constant 
voltage transformer.  The have a set of vices all their own 
but do work quite well.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com