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Re: [Amps] Solid State Amps

To: "Winfried Kriegl" <>, <>
Subject: Re: [Amps] Solid State Amps
From: "Carl" <>
Date: Fri, 17 Oct 2014 21:02:53 -0400
List-post: <">>
Thanks Win, I was going to ask my #2 son who just retired from the USAF and is living in Garmisch for the translation but he was already in bed. He speaks German as a native and has decided to stay and work there.


----- Original Message ----- From: "Winfried Kriegl" <>
To: <>
Sent: Friday, October 17, 2014 6:13 PM
Subject: Re: [Amps] Solid State Amps

It´s a perfect german translation, Carl  :-)

73 Win DK9IP

Am 17.10.2014 23:56, schrieb Carl:
Ive noticed over a wide swath of amp and other forums that SS is
becoming more popular but seemingly misunderstood by most even more so
than tube amps.

The majority appear to be the newer generation of instant hams that have
a problem understanding how to tune a tube amp, especially those models
that are even marginal  for experienced users.

Also our rapidly aging older generation is having some problems tuning
and even concentrating on tuning and destroy things in the process. The
weight of a tube amp is another serious concern

Neither group should be let inside a tube amp without training or
assistance for their own good.

Now the bad news....the lack of a quality SS amp at the price they want
to pay. Yes, some have the money and there are a few choices but the
majority appear to gravitate to MRF 150 amps that are being pushed to
the limit witout any feedback circuitry and claims of "exceptionally low
SSB distortion compared to tube amps".

Yet nowhere are any IMD specs published that I could find.

So for around $3K you get a 1200W amp, and you are warned about extra
heat generation if the SWR is over 1:1!  Hmm, it sounds as if they are
brainwashing you into also buying an antenna tuner.

As my Yiddish friends from Brooklyn used to say: "velkh a fun drek"

Or from my German grandfathers: " Was fur ein Haufen Scheisse"

Apologies for any translation errors as I had to cheat and use an online
translator; couldnt remember parts of the phrase; its been 60 years or
so (-;


----- Original Message ----- From: "Manfred Mornhinweg" <>
To: <>
Sent: Friday, October 17, 2014 2:24 PM
Subject: [Amps] Solid State Amps

Dear all,

Dan touched the subject of solid state amps, and Louis was quick to
state that most hams would prefer a good tube amp. If you ask me, the
performance/cost ratio will dictate what hams finally prefer, rather
than any philosophical concepts.

So, what we need to finally move tubes out of the ham realm (except
for those who really love tubes, of course), is making solid state
amplifiers that are better and less expensive than tube amplifiers.

And the best approach to do that is _not_ by porting tube era
technology to solid state devices, nor is it to keep building copies
of Helge Granberg's designs forever. These approaches simply produce a
poor performance/cost ratio, when taken to the 1500W level.

Let's see what the weaknesses of solid state amps are:

- Heat. Solid state devices simply are very small, and don't tolerate
extreme temperature. So, a high power, class AB, solid state amplifier
will ALWAYS be problematic in terms of cooling. It will need large
heatsinks, fans, heat spreaders, and careful design of the thermal
aspects, just to start becoming viable.

- Fragility: RF power transistors are usually run very close to their
absolute maximum voltage spec, close to their maximum current spec,
and at or even above their rated thermal capability, with the heat
sink system used. Any problem like non-perfect SWR, relay glitches,
etc, and their survival depends 100% on excellent protection
circuitry. Tubes instead are so forgiving that in practice they don't
need protection circuits in most cases, or some tubes need simple
circuitry to protect against excessive screen or grid dissipation, but
not much else.

- Poor linearity: Both bipolar and field effect transistors are less
linear than tetrodes and pentodes, and while better than triodes, they
don't have enough gain to use them in grounded base/gate
configuration. So, they depend on negative feedback or other external
means, to arrive at good IMD specs. Many designers still don't grasp
this concept well enough, and try building solid state class AB
amplifiers without negative feedback, getting horrible IMD performance.

Now some people have tried, and are still trying, to solve these
problems by brute force methods: Use lots of transistors, on big
heatsinks, run them well below their maximum specs, use UHF
transistors at HF to get enough gain that allows using lots of
negative feedback, and put in complicate protection circuits. The
results of these efforts can work reasonably well, producing
amplifiers that are instant-on, no-tune, reliable, and about as large
and heavy as tube amplifiers - but the solid state ones tend to be
more expensive, done that way. And often the implementations are
simply wrong and unsafe, for example by relying on an SWR sensor
placed between the low pass filters and the antenna.

What we need to do, my dear friends, is something totally different.
For starters: Forget class AB, because it's too inefficient, and
forget Granberg's push-pull configuration, because it has no inherent
protection features and needs problematic transformers.

Instead of Granberg's design, we need to place our RF power
transistors in half bridge or full bridge configurations, with
effective antiparallel diodes. This configuration eliminates all risk
from overvoltage. Then we need to run our transistors in switchmode,
_not_ in any linear mode, to get rid of the heat that causes so much
trouble. Then we add simple current sensing with quick shutdown, to
protect against severe overcurrent situations. We need to take the
highest voltage transistors we can, up to a level of 400V or so, to
get rid of the ultra low impedances that result from low voltage
operation, and which are hard to handle. And instead of a broadband
transformer (not very easy at the kilowatt level), followed by
relay-switched low pass filters, we should use relay-switched resonant
matching networks. That's no more complex than the low pass filters,
and the resulting Q is low enough to pre-tune these networks to each
band and then forget them.

And then, of course we need to add circuitry around the amplifier
block, to obtain a linear transfer function despite the switching
operation of the RF transistors. This can be done by RF pulse width
modulation of the drive signal, power supply modulation, bias
modulation, a combination of two or three of these, or any other
method. This is far more complicate than a traditional tube amplifier,
of course, but it uses cheap, small, widely available components, and
so it's inexpensive to implement.

The result would be an instant-on, no-tune, small, lightweight,
silent, highly efficient, reliable _and_ inexpensive legal limit

Anyone actually developing this concept to market maturity can put all
existing ham amplifier manufacturers out of business. A scaring
thought - for them!

Do you notice the logic in this? Going from class AB to a switching
mode achieves several important advantages:

- Cooling becomes very much simpler, cheaper, and silent.
- Power supply requirements are drastically cut down, producing
advantages in cost, size, weight, etc. A 1700W power supply can power
a 1500W amplifier.
- Power consumption is reduced a lot, an important selling point in
many countries that have expensive electricity. Maybe not in the US,
where it is almost free.
- The transistors needed are very much smaller and cheaper than those
needed for class AB, due to low dissipation requirements.
- A good active linearization circuit can produce far better linearity
than class AB with 10dB of negative feedback, and even better than
that of tetrodes.

And the difficulties involved in this approach:

- Finding ways to get around the limitations of present-day RF power
transistors, in terms of voltage-dependent internal capacitances, slew
rate limitations, and high voltage handling.
- Summonning the determination to do all the detail design work, and
break free from the idea "if Granberg did it that way, that must be
the best/only way".

Any idea, anyone?

Maybe we should start a collaborative open project, developing this
thing! The final goal: A solid state amplifier no larger nor heavier
than a typical HF radio, that can produce solid legal limit output in
all modes, with no time limit, with good IMD performance and high
reliability, a total parts cost around $500, and selling to those who
are too lazy to build it, for around $1000.

I'm just waiting for the right transistors to show up, and then I will
do it myself. With the transistors I know right now, I would get up to
the 40m band only, or at most to 20m, but not to 10.


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