[ARC5] BFO performance at lower B+ supply voltages.

[Dennis Monticelli]

Very true, Les.  Before the BFO fades out entirely it will exhibit a low
output.  It's this low injection level that causes the distortion.  I can
hear it in CW too. If I back off on the gain then it's better because the
ratio of signal to BFO improves, but then an already low audio volume gets
even softer.

Dennis AE6C



On Tue, Jan 20, 2015 at 3:44 PM, Leslie Smith <vk2bcu at operamail.com> wrote:

>   Dennis wrote that the first thing that 'dies' is the BFO.
>   True, because the BFO plate supply is fed thru a 'wopping big'
>   resistor.
>   The first indication of poor BFO operation is heard when listening to
>   SSB - distortion.
>   This is not so apparent when listening to CW.
>
>
>   73 de Les Smith
>   vk2bcu at operamail.com
>
>
> On Wed, Jan 21, 2015, at 09:04, Dennis Monticelli wrote:
> > FYI.  My re-cap'd BC-453B pulls 10mA off 60V.  Not much at all.  Of
> > course
> > you pay some price in terms of overall gain and audio output, but the
> > sensitivity is still good enough that antenna noise dominates.  As I drop
> > B+ further (heading for 24V) I find that the first function that dies is
> > the BFO.  Some radios are still running OK at 24V and some lose the BFO.
> > Maybe a fresher tube would make the difference.  I know some folks run
> > them
> > that low successfully.
> >
> > Dennis AE6C
> >
> > On Tue, Jan 20, 2015 at 1:39 PM, Bill Cromwell <wrcromwell at gmail.com>
> > wrote:
> >
> > > Thanks Dennis,
> > >
> > > I'm takings notes here and looking at what I have. My Kenwood doesn't
> > > "seem" to bothered as much so I will look at the power supply
> schematics
> > > but I suspect I am *hearing* less of the crud because of the system
> > > passband and much more is seen by the front end - bad! I was surprised
> by
> > > the small amount of current drawn by six tubes from the B+ at 45 and 90
> > > volts. I suppose I have become used to larger numbers for the plate
> current
> > > in transmitters. I have several hours on the batteries on the BC-453
> now
> > > and the batteries are still chugging away.
> > >
> > > I thought I had a used power connector with the built-in filters left
> from
> > > a swap-fest purchase that included two or three of those units. They
> are
> > > reasonably priced from places like Mouser, etc. I might purchase the
> > > individual parts and put them together to handle higher current for
> > > transmitter power supplies. A filter built heavier will surely not be
> > > harmed by *ANY* receiver.
> > >
> > > 73,
> > >
> > > Bill  KU8H
> > >
> > >
> > >
> > > On 01/20/2015 12:31 PM, Dennis Monticelli wrote:
> > >
> > >> On my BC-453 I either run batteries as you do, Bill, or I use HP bench
> > >> supplies, which have excellent output noise specs.  The local noise
> > >> environment is bad enough as it enters from the antenna without
> having to
> > >> worry about direct feed of line noise into the receiver circuitry.
> > >>
> > >> Dennis AE6C
> > >>
> > >>
> > >
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