I beg to differ.
I used the term "all things being equal".
Hence issues of shielding integrity, supply regulation and tuning apply in
the hypothetical case of the amplifier being pushed close to its limits and
a larger one working on the linear part of its transfer curve.
Headroom in amplifiers relates to their ability to follow transient changes
in signals, whether speech or keyed information.
The issue of the quality of the input signal to an amplifier applies equally
to low and high power amplifiers.
In the real world the budget amplifier typically has a weak power supply
which sags under load and increases the distortion products.
Also in the real world the budget amps tend to be poorly shielded and lack
features such as vacuum variables which typically show lower impedance to
vhf than breadslicers do, hence the tanks work more like they should in
theory.
One could go on at length.
The same considerations apply to audio amplifiers: the overbuilt ones look
better when the output is analysed and sound better to the ear.
Also issues of reliablity and abilty to keep on spec over time arise.
I stand by my point that long run the overdesigned amp is likely to be a
better economic and functional choice.
73
Baz ZL1DD
end
Barry Kirkwood PhD ZL1DD
Signal Hill
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
www.waiheke.co.nz/signal.htm
----- Original Message -----
From: Tom Rauch <w8ji@contesting.com>
To: J. Bradshaw <ac6tk@cybertime.net>; Barry Kirkwood <bjk@ihug.co.nz>
Cc: <amps@contesting.com>
Sent: Tuesday, 09 January, 2001 12:17 PM
Subject: Re: [AMPS] Advice about what linear to buy
>
> Hi Jim,
>
> > overhauls. A small amp pushing the limits of its linearity will cause
more
> > TVI and side splatter than a larger one putting out the same power,
again
> > assuming similar operating modes.
>
> TVI has absolutely nothing to do with "headroom" in the PA. It is
> entirely a function of the layout and shielding integrity.
>
> "Side splatter" (as opposed to "up and down splatter") is not
> necessarily related to headroom either. An amplifier capable of
> 3000 watts being operated at 500 watts can easily have more IMD
> than an amplifier capable of 550 watts operated at 500 watts.
>
> By far the most common cause of IMD is improper tuning, or
> improper screen and bias systems in tetrodes when the IMD is
> predominantly from the PA.
>
> In the real world, most IMD is from the exciter with any reasonable
> amplifier design.
>
> It's amazing how bad most rigs have gotten, and this especially
> aggravated because some people think that a just because a radio
> can put out 200 watts they can turn the internal power limiting
> controls up to 130 watts or more without ill effect.
>
>
> 73, Tom W8JI
> w8ji@contesting.com
>
> --
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>
>
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