[AMRadio] B&W 5100B Modulation Update

Mike Dorworth K4XM k4xm at arczip.com
Wed Oct 13 12:47:47 EDT 2004

you have either a bad rectifier or most likely the capacitors in the power
supply are shot.. Mike K4XM
----- Original Message ----- 
From: "Tom Elmore" <tom at telmore.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, October 13, 2004 12:34 PM
Subject: [AMRadio] B&W 5100B Modulation Update

> Now that I have had some time to troubleshoot the B&W 5100B modulation
> is what I found. The B+ is around 600 volts with no modulation and I as
> start to modulate and watch the scope when it reaches about 50% modulation
> the B+ drops from 600 to around 400 volts.  I changed the final and
> modulator 6146 tubes and see the same results. The original modulation
> transformer has been replaced with a Chicago Standard Transformer
> Corporation # A-3891.   When I remove B+ to the final's and terminate the
> modulation secondary into a resistive load of about 6k ohms I still see a
> significant drop in  B+ as I start to bring modulation up. I don't have
> original mod transformer and the manual I have doesn't say what the
> impedance should be.  I have tried various other tap settings on the
> transformer secondary and don't see much of an improvement in reducing the
> amount of voltage drop. I wonder if it is possible that this mod
> just will not work with this unit. Anyone have experience with mod
> transformers using 6146's as finals and modulators?
> Thank You
> Tom Elmore KA1NVZ
> Anchorage  Alaska
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