Hamarlund HX 500 Power Transformer

Allan Tyson bigaltyson at EARTHLINK.NET
Wed Oct 6 01:27:28 EDT 2004

I need to replace the power transformer in my Hammarlund HX 500.
Dahl will manufacture one but they only have the specs of the original
model transformer ( Hammarlund Part # K42351-1 )  which lists the
secondary voltages as 900 320 110 0 320 900 . The original had a
12.6 V winding for the pair of 12AX4 Rectifier tubes used in the HV
Supply. Approx a year after introduction Hammarlund changed the
design of the Power Supply by replacing the pair of 12AX4's with a
single 5RU4GYB and replacing th Bias Rectifier Tube with a Solid
State Rectifier. They didn't change any other components in the HV
Supply but did raise the value of the dropping resistor in the Bias
Circuit and increase its rating from a 1 to a 2 watt. They also reduced
the bias voltages from -100V & -50V to -90V and -45V. I'm not sure if
the reduced bias voltage(s) are solely due to the change in the value
of the dropping resistor or if there was an associated change in the
bias voltage tap on the secondary.
 Even more troubling are the changes in the LV Circuit. Three of the
dropping resistors have been significantly reduced in value but the
associated Low Voltages have also been lowered indicating that the
LV Taps on the secondary have also been changed to deliver a lower
 If anyone has the voltages of the secondary of the later model
transformer ( Hammarlund Part #K42351-3 ) or has an HX 500 with
the later transformer ( models manufactured after the change or those
that installed the replacement transformer and resistors furnished by
Hammarlund in an Upgrade Kit ) and would let me know the voltages
at the transformer of the LV and Bias Taps I'd very much appreciate it.
 73's and Thanks
 Al Tyson

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