[AMRadio] B&W 5100B Modulation Update

Bob Bruhns bbruhns at erols.com
Wed Oct 13 17:05:43 EDT 2004

Tom - if that's an A-3891, it isn't enough for a pair of 6146s.
It's rated for 15 watts as I feared.

(Stancor and Chicago Standard appear to be the same company)

But if it's really an A-3894 with worn paint, then you may be in

  Bacon, WA3WDR

----- 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 here
> 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%
> the B+ drops from 600 to around 400 volts.  I changed the final
> modulator 6146 tubes and see the same results. The original
> 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 the
> original mod transformer and the manual I have doesn't say what
> impedance should be.  I have tried various other tap settings on
> 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
> ______________________________________________________________
> AMRadio mailing list
> Home: http://mailman.qth.net/mailman/listinfo/amradio
> Help: http://mailman.qth.net/mmfaq.html
> Post: mailto:AMRadio at mailman.qth.net

More information about the AMRadio mailing list

This page last updated 21 Feb 2018.