AM modulation is a multiplication (mixing) process. Without a switch
(amplifier driven into cutoff) there is no multiplication of the signals.
The variation in plate voltage due to power supply ripple will be seen in
the output as addition and subtraction of the main signal and ripple voltage
but at a very low level if the amplifier is linear. No side bands are
created as they are in an AM signal.
73
Gary K4FMX
_____
From: TexasRF@aol.com [mailto:TexasRF@aol.com]
Sent: Thursday, October 03, 2013 10:44 AM
To: ww1c@outlook.com; garyschafer@comcast.net; amps@contesting.com
Subject: Re: [Amps] Plate modulation from power supply ripple?
Hi All, even if the plate current did not change, wouldn't the changing
plate voltage result in changing power input and corresponding changes in
power output?
That sounds like modulation as well.
Taking this to an extreme, removing the filter C altogether, any hum
modulation then? How much?
73,
Gerald K5GW
In a message dated 10/3/2013 8:35:17 A.M. Pacific Daylight Time,
ww1c@outlook.com writes:
Hi Gary, All
I was thinking about your statement and looking a typical tube anode
characteristics (curves).If I read this correctly, change in plate voltage
does cause a change in plate current.Is this not plate modulation? I am not
sure if the operating class changes this.Perhaps I need to simulate this
too...
Thanks
MarkkuWW1C
> From: garyschafer@comcast.net
> To: ww1c@outlook.com; amps@contesting.com
> Subject: RE: [Amps] Plate modulation from power supply ripple?
> Date: Wed, 2 Oct 2013 12:36:06 -0500
>
> You don't hear the ripple because it does not modulate the linear
amplifier.
> If you were to run the amplifier in a non-linear mode such as class C then
> it would plate modulate it.
>
> 73
> Gary K4FMX
>
> > -----Original Message-----
> > From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Markku
> > Oksanen
> > Sent: Wednesday, October 02, 2013 12:40 AM
> > To: amps@contesting.com
> > Subject: [Amps] Plate modulation from power supply ripple?
> >
> >
> > All
> > I was simulating (with LTspice) a three phase power supply where the
> > secondary is in star configuration with full wave rectification. You can
> > get also a second voltage from this by connecting to the center of the
> > star, this voltage is half of the full wave rectified voltage and is
> > only half wave rectified (per phase), 3 pulse in stead of 6 pulse for
> > the higher voltage.
> > It turns out that even relatively high value (tens of uF) filter
> > capacitors would leave some 10% of ripple on the lower voltage. Now the
> > question is: How much plate modulation this make? The ripple frequency
> > is 150 Hz and to me this looks like your regular high level, plate
> > modulated AM transmitter. Why do we not hear this on a typical signal
> > if it is there?
> >
> > MarkkuWW1C
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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