[AMRadio] B&W 5100, 5100b differences?

Mark Bell bell at blazenet.net
Mon Mar 14 11:39:56 EST 2005

----- Original Message ----- 
From: "Jim Wilhite" <w5jo at brightok.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Monday, March 14, 2005 10:59 AM
Subject: Re: [AMRadio] B&W 5100, 5100b differences?

> I can't tell you much but some of the differences are, the 5100B was
> designed to provide phasing SSB with the addition of the 51SB-B,which
> derived it power from the 5100B.  The 51SB had a power supply built in and
> required some modifications to the 5100 to make it work.  The 5100B has a
> switch that provided neutralization to the final plus switched the RF from
> the mixer section to the SSB exciter, the 5100 did not have that switch.
> The 5100 was designed for AM and CW work only.

The original 5100's were designed for AM and CW work only, but later 5100's
were "kinda" designed for SSB work.  I call the later models of the 5100 the
"S" variant, as they had the AM/SSB switch factory installed inside the
radio -- you had to lift the lid to change the switch, as it was localted to
the left and behind the finals.   You could also purchase an after market
kit from B&W to add this switch to the non "S" 5100s. You needed the switch
installed (one way or the other) to use the 51SB.    Along with the switch
kit came an addendum that had you change several components.  I have the
addendum sheet and the kit instructions somehwere in the shack.    I'm
wondering if the addendum sheet had any changes in the audio circuit to
limit the audio for the 51SB-B.  I'll have to dig it out and check.

> The changes you noticed in the modulator/audio section were performed to
> limit the passband of the audio on AM which also benefited SSB.  You will
> note that a cathode resistor was switched in for AM whereas the 5100 had
> that resistor there permanently.  There was also a couplate that
> the audio between the second stage audio and audio driver to the
> Another resistor and a cap to ground was added to help this limiting as
> to the grids of the modulator tubes.

I've wondered about removing the couplate and just replacing it with a
different network that doesn't restrict the audio quite as much.  I get good
audio reports with my stock 5100B, so I've never had any real inclination to
do the change, but it's crossed my mind from time to time.

> Other than that, I don't see much difference.  I just obtained a 5100 that
> will pick up this Friday so will be able to look more closely, but the
> comment by Robert is intriguing.  The modulation transformer in the 5100B
> does look to be a little light for it's duty.
I've got a 5100B/51SB-B on the air, and a non "S" 5100 on the shelf.  The
5100 works, but needs cleaned, filter caps changed etc.  I pick up my "S"
variant 5100 just before Easter.  It's grungy, and will require the typical
cleaning and parts replacement.  I plan to use this with the 51SB that's
lonely on my shelf.

The last time I chatted with Mo W5KD (SK), he gave me the power supply mods
he made to his 5100 to beef it up.   Mo also did some audio mods to his
5100, and if you've ever talked to Mo on the air, he had one very sweet
sounding 5100.    My non "S" 5100 has a 32V2 mod tranny in it, but I've
since acquired a replacement tranny.  Anyway, because of that, he didn't
bother giving me the audio mods.  Anyone know what they were?

73 Mark K3MSB

> 73  Jim
> W5JO
> ----- Original Message ----- 
> From: "George KB2Z" <Thermionic_Emission at earthlink.net>
> To: "amradio-mailman.qth.net" <amradio at mailman.qth.net>
> Sent: Monday, March 14, 2005 8:30 AM
> Subject: [AMRadio] B&W 5100, 5100b differences?
> > Morning all,
> > Could anyone on the list tell me the performance differences between the
> > B&W 5100 and 5100B?
> > On the schematics the changes in the audio/modulator section jump out.
> > one better than the other? Any thoughts or opinions would be
> > Thanks in advance, George KB2Z
> >
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