[AMRadio] B&W 5100B Progress Update

Patrick Jankowiak recycler at swbell.net
Sun Oct 17 11:52:27 EDT 2004


Looks like you got it fixed. The way ham gear is (was/is?) 
sometimes made, things might have to be just right to get the 
specified performance. I don't know much about the B&W, but maybe 
without the original modulation transformer, ther match is not 
quite perfect, so therefore slightly less performance. I hate to 
suggest it, but if you run maybe 80 watts, how much modulation do 
you get?

Just for curiosity, can you tell the parameters of the circuit if 
you have measured them? I'd be greatly interested in the numbers. 
Maybe something will suggest itself for imporvement under 
scrutiny if you want to go to the trouble of getting the data.

AM mode carrier condition:
-PA B+ volts
-PA screen volts
-PA Plate current
-Power out
-modulator plate current

modulated conditions:
(sinewave at maximum % obtainable without clipping in the modulator)

-modulation %
-PA B+ volts
-PA Plate current
-Modulator B+ volts
-Modulator plate current
-Modulator screen volts
-Modulator bias volts
-rms or average value of 120Hz ripple on B+

-Model # of replacement transformer
-connections made for impedance selection
-DC resistance and voltage of the entire B+ winding of the power 
-DC resistance and value of any HV B+ choke
-value of filter capacitance on B+
-rectifiers (two 5R4 I think you said?)


From: "Tom Elmore" <tom at telmore.com>
Subject: [AMRadio] B&W  5100B Progress Update

   I finally had time this week to install the Stancor 
replacement modulation transformer for my B&W 5100B and have 
found a set of taps that work on both the primary and secondary 
windings. I can make full carrier output of at least 100 watts 
but the modulation is only making about 85 to 90 % before it 
starts to flatten out on the scope and distort. I have changed 
both the modulator and final set of tubes and still get about the 
same percentage of
modulation. I was hoping to make at least 100% easily.  Someone 
mentioned recently that this was a characteristic of this unit 
and I wonder if it's power supply limitations or some other factors.

Thank You
Tom Elmore KA1NVZ
Anchorage, Alaska

More information about the AMRadio mailing list

This page last updated 16 Dec 2017.