[ARC5] BC-453 Current Draw - update

[Dennis Monticelli]

Bill,

Thanks for the followup report.  I think the weak spot in the ARC-5 for
dynamic range is the mixer, as it almost always is in a superhet.  In my
BC-453 the mixer's LO doesn't even start up until 52V (and then clings to
life until the supply drops below 30V) so I suspect the starved mixer
overloads pretty easily at 45V in most of the receivers.  It may be
headroom of just weak chopping action in the 12K8.

Dennis AE6C

On Mon, Jan 26, 2015 at 4:19 AM, Bill Cromwell <wrcromwell at gmail.com> wrote:

> Hi,
>
> We had some animated discussion on this thread and I have an update using
> battery power with my BC-453s. I stated that the radios will operate at 45
> volts. Some others have examples where individual radios may not operate
> with B+ that low. Trying things with two different receivers I get the same
> result. But as the B+ gets reduced the exact setting of the gain control
> gets more critical. That was noticeable and irritating with about 10 or 15
> minutes of operating time.
>
> If the gain is set too high loud signals may hurt our ears. The radio may
> overload - exhibited by a dramatic increase in "noise". If the gain is set
> too low the weaker signals will drop out - or even the strong ones if it's
> low enough. Operating with 90 volts the gain control "sweet spot" (not too
> much, not too little) covers a wider, very comfortable range of operation.
> At 45 volts it's really touchy and any variation drives the radio into the
> ditch. The two radios I played with (logging NDBs) got better when I added
> just one 9-volt battery to the pyle for ~54 volts B+. The sweet spot was
> tolerably stable. I suppose I will be operating my radios at ~90 volts B+.
> Your mileage may vary.
>
> Probably a stock radio with only 45 volts also lacks adequate headroom
> before some clipping or flat-topping occurs (I didn't break out the scope).
> If we modify the radio by changing some resistor values as mentioned by Les
> and some others these "issues" might resolve. In my own mind that engages
> other problems such as the next radio enthusiast who gets the radio and
> applies 250 volts B+ will be quite unhappy. I do expect the radio will
> outlast me.
>
> 73,
>
> Bill  KU8H
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