William Warren wrote:


Lazy Senior: I feel your pain!

If I were you, I'd look for any of the "2KW PEP" linears that come up on
Ebay or at hamfests, such as an L-4B: any linear rated for 1KW key-down
continuous input will work fine.

If you are using coax, don't forget to check it for breakdown voltage
before loading up: AM peaks will put a lot of strain on older cable.
Don't ask me how I know ;-).

HTH.

William


William

Thanx for the info. It seems like most hams I work on AM that use amps
are using linear amps, but much to my surprise there are many here in
this group that are against using linears.

Lazy (yes) Senior (yes)

COLIN LAMB wrote:

The modern amp covers 160, though, along with the other bands, so of one is
lazy (hence his name), the linear is a reasonable approach.

Colin K7FM



Colin
This is what I suspected when I first asked my question, but many
posters here infered it was not a reasonable approach.

Thanx
Lazy Senior

Lazy Senior wrote:
Mike Andrews wrote:

The FCC thinks it's valid. Whether or not it's in QRZ.com is irrelevant.

Hmmm, a new nocoder vanity call? No, most tech lites I know have common
sense, Uncle Peter acts like an Extra.........

THat's because he's an Extra.

I'm not sure where you're getting your data, but the FCC has this for
Peter:

Licensee Name BERTINI, PETER J
Operator Class Amateur Extra

You _could_ have looked it up for yourself.

--
Mike Andrews, W5EGO

Tired old sysadmin

Lazy Senior wrote:

William

Thanx for the info. It seems like most hams I work on AM that use amps
are using linear amps, but much to my surprise there are many here in
this group that are against using linears.

Lazy (yes) Senior (yes)


Well, you can go either way, but linears are simpler, self-contained,
easy to service, and they help keep the room warm.

High level plate modulation was "The way to go" before the FCC switched
to measuring output power instead of input, and I understand why some
hams would want to use Class C finals and high level modulation, since
that's the best way to get the most efficiency out of a 1 KW input rig.
Now that we measure output power, I don't feel that the added hardware
and maintenance of using high-level modulation is justified. Others may
disagree.

My attitude is "If it isn't fun, stop doing it" - this is a _hobby_, but
somehow a few hams never get the word. If having a "big iron" rig is
what turns you on, go for it. If you want to maximize efficiency and
homebrew a rig from scratch, there are Class E designs available using
computer components to good effect. If you're interested in a smaller
footprint and interoperability with SSB or other modes that need
linears, then a linear is a practical alternative.

FWIW.

William

--

William Warren

(Filter noise from my address for direct replies)

The modern amp covers 160, though, along with the other bands, so of one is
lazy (hence his name), the linear is a reasonable approach.
Colin K7FM

This is what I suspected when I first asked my question, but many
posters here inferred it was not a reasonable approach.
Lazy Senior

I use low-level modulation and a linear amplifier to work AM. My
advice in selecting a linear amplifier for that mode is to focus on
the heat dissipation capability of the final devices, be they tubes
or transistors. Although the theoretical efficiency of a class-B
amplifier is something like 67%, that applies to a signal swinging
the amplifier between cutoff and saturation. For the carrier-wave
level, which will be 1/4 the peak output power, the operating point
will be in the regions of the characteristic curves that are much
less efficient. I typically get 25-30% from my SB-220 with a
250-watt carrier output power. Worst-casing a desired 375-watt
carrier level with 25% efficiency gives a final-power-dissipation
requirement of 1125 watts - a stretch for a pair of 3-500's, somewhat
easier with a 3CX1200 and easier still with an 8877/3CX1500.
The steady-state power-supply requirements are also pretty strenuous -
1500 watts - although most recent designs (Ameritron AL-1500) are
capable of this.

The efficiency argument against using a linear and in favor of
high-level modulation is seen to be fairly strong. However there
are a few additional factors to consider: As noted by another
poster, the modulator has to be powered up and has its own efficiency
issues. Also, using a linear amplifier rather than a Class-C final
reduces the harmonic-attenuation problem considerably (as well as
neighborhood TVI complaints). Modulation done at low levels is
more "controllable" with modestly sized components for splatter
filters, negative-peak loading/clipping and negative feedback. I
use an SSB transceiver (a Kenwood TS-850) for the extreme form
of this "modulation control", since my transmit signal is passed
through the same 6 kHz IF filter used for reception - effectively
filtering out splatter and out-of-channel IMD. The last advantage
of linear amplifier use, stated in the beginning of this thread, is,
of course, the ready availability of commercial units, both new and
used. For a dual-mode station (AM and SSB), the investment in
the amplifier pays a double dividend while, at the same time,
breathing new life into (and a whopping signal out of) many cherished
vintage low-power AM transmitters.

Jim, K7JEB

William Warren wrote:


My attitude is "If it isn't fun, stop doing it" - this is a _hobby_, but
somehow a few hams never get the word.

FWIW.

William


William
We think alike. Too many hams take hamradio way too seriously. Its not a
way of life, its just a small part of my life.

I am a long time ham -45 yrs-. After posting here for the first time I
was called a troll simply because I asked a stupid question which I
didnt know the answer to. Altho having been a ham for so long, I am not
particularly tech inclined.In other words my life doesnt revolve around
electronics and theory.I know fom experience many hams look down on
those who are only Tech lites or Generals. It is no surprise young
people dont want to join our ranks.

You were one of many who gave me a very informative answer in language I
could understand. I only wish more had your attitude.

Thanx and hope to CU on AM
Lazy Senior

K7JEB wrote:

I use low-level modulation and a linear amplifier to work AM.

Jim
What linear amp do you use?

Lazy Senior