[Amps] Decline of homebrewing?

[Rob Atkinson]

>
> I recently bought a 1955 ARRL Handbook and a Bill Orr book from the 1960s so
> that I could have references that cover tube theory and practice.  Nothing
> recent covers it.
>

You need a lot more than that.  Go to hamfests and look for and start
buying up QSTs from before around 1955, ditto for handbooks, don't
overlook tube manuals, the RCA Redbook, IIT Engineers Handbook,
anything by Terman, and Sterling, West Coat radio handbooks dating
back to the 1930s, the entire run of Electric Radio, issues of Radio
magazine before it moved to the east to become CQ, the LaPort's
antenna book,  metal working shop textbooks, that should keep you busy
for a while.


> Let's face it: SSB transmitters control the output power by means of ALC. It's the best method found to date, as far as I know, at least for voice transmission.

It is a cheap and poor way of controlling voice peaks.  In the typical
solid state transceiver, the output is sampled and converted to a
control voltage that is fed back to a VCA in an early low level stage
of amplification, to automatically reduce the gain of the low level
driver.  The obvious problem with this scheme is that by the time VCA
acts, the horse is through the gate and out on the loose, i.e. that
big RF peak is gone.  If the VCA has slow recovery it may catch other
RF power peaks and limit them, but it is really a poor scheme and
you'll never find it in any professional equipment as far as I know.
Far better is to employ a fast broadcast peak limiter at baseband but
that costs $$$ and 99% of hams won't want to spend it.  A manufacturer
could build such a circuit into a rig at a significant additional cost
but now you've added something that most hams are not trained to
employ, won't understand or appreciate.  The ALC method is far cheaper
but inferior.

73 & happy new year

Rob
K5UJ