[AMRadio] B&W 5100

[Donald Chester]

Jim W5JO wrote:

"You can change them to .005 and change the cathode by pass cap on the 6AQ5
to 25 uf.  Those are the mods that Moe, W5KD used in his and everyone raved
about his audio using a EV 638.  The set doesn't need a lot because of the
problems Dave pointed to.

The B model changed to couplates and restricted the bandwidth to comply with
the narrower signal for SSB and the push by the ARRL for narrower
bandwidths.  The cathode resistor in the B model was different in that
cathode circuit as well."

>> I have a 5100B that is unmodified....still has the couplate and no 
>> mods other than the usual cap replacement.
>> The rig has barely 100W output so anything you do to add any bass or 
>> reduce the treble will make it even harder to make a contact.

I don't know why anyone would WANT to reduce the treble, but a moderate
boost in lows in the range between 100 ~ and 300 ~ won't hurt
intelligibility, while making it more pleasant to listen to. The first thing
I would do would be to get rid of those damned couplates, couplettes or
whatever you call them. The Globe King 500 is another rig that used them.
Roger, N4IBF (SK) wasn't happy with the sound of his, so I advised him to
remove the couplates and replace them with conventional R-C coupling
components (plate resistor, coupling capacitor and grid resistor) with
values chosen to maintain flat response down to about 80 Hz. Values for the
most widely used tubes from that era can be found in the chart in the 1950s
ARRL Handbooks. Roger chose values from that chart, but increased the
recommended coupling capacitance by about 50 or 100%.  He was utterly amazed
at the reports of how much better his audio sounded, and it was more
intelligible to boot. Chances are, the input grid resistor to the first
audio stage is too low in value, typically anywhere between 500k and 1 or 2
megohms (I have even seen rigs that used as little as 50K!). Replace it with
a 4.7 meg 1/4 or 1/2 watt film or composition  resistor (measure with an
ohmmeter first, especially if it a junkbox resistor). 

That  should sound great with a good UNAMPLIFIED crystal D-104. If it's one
of the more recent "CB versions" with the built-in amplifier in the base,
remove the amplifier (I would recommend tossing it in the trash but if you
prefer you can just disconnect it), and re-wire to feed the transmitter
directly from the crystal element.

Don k4kyv