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Re: [Amps] Solid State Amps

Subject: Re: [Amps] Solid State Amps
From: "Col. Paul E. Cater" <>
Date: Fri, 17 Oct 2014 18:16:12 -0400
List-post: <">>
*"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.*"

Oh come on------Let's not degrade this into a conversation about code, no
code.  Not that I disagree about the "instant hams".  We are not talking
about that but, SS or big old  tube(s) amps.

Some of these new kids are reasonably smart.


On Fri, Oct 17, 2014 at 5:56 PM, Carl <> wrote:

> 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
> (-;
> Carl
> KM1H
> ----- 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 amplifier.
>> 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.
>> Manfred
>> ========================
>> Visit my hobby homepage!
>> ========================
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