[Amps] 4-1000 HB amp

[Dan Hearn]

Ken, I accomplished the same thing using a triac light dimmer wih a rotary
knob. Works great. I think your calcs do not take into account that the
filament R varies as the voltage changes.
73, Dan, N5AR

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
Behalf Of k1um at bellsouth.net
Sent: Thursday, April 24, 2008 8:13 AM
To: Amps at contesting.com
Subject: [Amps] 4-1000 HB amp

I have been lurking for a while here...  I need a 2nd amp for SO2R
Contesting - my current amp is the Ameritron AL1200  -
I have been salting away 4-1000 parts over the last 40 years and decided to
HB amp#2

The power supply is a remote unit with ambilical to desk top amp deck. Has
variac input 220v, P dahl xfmr and home grown chasis/box on wheels

My questrion is since the 4-1000 uses 7.5 fil at 21 amps - I want to switch
resistors to the fil to yield 1/4, 1/2, 3/4 voltage and finally full fil
voltage....

my calc's=
P=IE=7.5*21=157W FIL SIDE
I=157/120=1.4 AMP PRIMARY SIDE [ROUNDING UP]
SO for
3/4V=30V/1.4I =23  OHMS
1/2V = 46 OHMS
1/4V  =69 OHMS

IS my calculations about right???

KEN K1UM
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