[AMRadio] B&W 5100

Fri Jul 5 00:17:51 EDT 2013

Don mentioned the RC coupling replacement for the couplates in the GK 500....
The improvement is positive, but it also increases the gain through 
the audio chain.
Had to keep the input pot about 2 on a scale of 10 when using the D-104.

Perry

At 12:43 PM 7/4/2013, Donald Chester wrote:
>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
>
>
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