Gary K9GS wrote:
> This has been an interesting thread. Along the same lines.....I wonder why
> someone doesn't offer a well engineered kit amplifier?
The same reason Heath doesn't sell kits any more. Economics! Those who
build are a very small number.
> Basically a
> modernized SB-220 possibly using different tubes?
Actually the 3-500 is still the most popular tube, it's relatively
inexpensive and fairly tame and with enough voltage it'll run the legal
limit without straining.
> Is there possibly some
> FCC regulation preventing this??
>
>
Nope! It would require the FCC's blessings just like the ones being
sold, but that's the only requirement.
However, how many hams do you know that you would be comfortable with,
poking around inside your amp with all that high voltage? I have an
idea that at least part of the problem is our litigious (sp?) society.
Maybe not the ham, but relatives and next of kin. Even signed Waivers of
Liability offer very little protection from the one signing it and none
from the next of kin.
> Maybe two models, a KW class and a legal-limit class.
Heath did that for years and closed shop. Maybe there's now a niche
market for something like these, but it'd likely be a small portion of
the overall market for amps. Would the market be large enough to support
those doing it? Most current amps are built by relatively small
operations, so it'd have to be small as well. Maybe two or three hams
could do it, but remember it would have to survive the cost of receiving
the FCC's blessing and make enough money to keep the families of those
involved happy. It takes business and market savvy as well as a
thorough understanding of amps to do something like this. Then there is
the problem of "how rugged an amp or amps would you sell in kit form?"
There will always be those who will push an amp for everything it can do
which may be well beyond the ratings of the tube(s) and/or power supply
and then blame the manufacturer for providing parts of insufficient
capability. It reminds me of the early 8877's that had higher gain and
lower drive requirements. Some hams were driving them with the full
output of their exciters as the tube would do it even though it could
reach its design limits with something like 50 watts or less and those
things will put out about 2200 watts. I believe it was Carl who said
Some one was blaming it on parasitics.
> Perhaps even a solid
> state AMP.
>
>
Solid state is a different animal. The transistors are expensive and
very fragile. Given a big voltage spike and a tube will normally just
ignore it. They might blush a bit if you drive them too hard, but
recover quickly (most times) Even the expensive, high powered
transistors can be wiped out from the static you pick up walking across
the floor. Even a microsecond of too high a voltage will take them out
and maybe no more than a few milliseconds of excess current. Even the
large, high power transistors are small physically and that makes heat
transfer to the heat sink problematic even when using exotic heat
transfer compounds such as "Arctic Silver" which is expensive.
I use it on CPUs and it's very effective. Given a legal limit amp you
have to get rid of the heat through an area that is likely to be less
than 2% to 5% of the radiator area on a single, small, power tube like
the 8874.. So you parallel two transistors to run the power that one is
capable of just to get enough area to safely transfer the heat. Even
then the delta T is pretty high. Then run them push pull. The Tokyo
Hy-Power HL-1.5Kfx gets 1KW PEP and CW output on HF from just 4
transistors. I can purchase a much more rugged 4CX-1500 for less money.
You will probably spend nearly as much on the protective circuits as the
whole rest of the amp. The basic amplifier runs about the power level of
entry level amps and costs about $3,000. To add the capability of
running the legal limit with some excess capacity now called overhead,
more than doubles the price.
The no tune, instant on, auto band switching, legal limit amps are
great, but they come at a price and not just the monetary one. They
require a low SWR to get maximum power out and by low I mean less than
(>)1.2:1, more often, less than 1.1:1. That means an antenna tuner and
retuning even after minor excursions 20 KHz or so on 40 meters. Of
course there is now the auto-tuner which is also fantastic and almost a
necessity for solid state amps if you do much moving around on 160, 75,
and 40 meters. OTOH I did it with a pair of MFJ 989C tuners and an
antenna analyzer and it worked very well. Switch in the noise bridge,
adjust tuner, switch back to amp with no additional tuning. No on the
air signal required at all.
There are some adventuresome hams (couple even here on the reflector)
who are working on some solid state amps at the legal limit level. Even
with help from some well known manufacturers it's a rather daunting task.
> The kit amplifier would be able to purchase components in volume, keeping
> the cost down.
>
> Anyone know how many amps Heathkit sold anyway?? I'll bet it was a lot.
>
We now live in a different society as hams and individuals. Would what
worked then, work now. Remember Heath started out small and grew like
crazy in size and offerings. Then the market dried up abruptly. This was
about the same time the attendance for most swaps dropped off and became
more tire kickers than really interested purchasers. This did not
coincide with the economy dropping off either. It did coincide with
what a couple of manufacturers did though. Whether by chance, I don't know.
73
Roger (K8RI)
> 73,
>
> Gary K9GS
> ++++++++++++++++++++++++++++++++++++++++++++++++
> K9GS
> Gary Schwartz email: k9gs (at) arrl.net
> Check out K9NS on the web: http://www.k9ns.com
> Society of Midwest Contesters (SMC) http://www.w9smc.com/
> GMDXA http://www.GMDXA.org
> ++++++++++++++++++++++++++++++++++++++++++++++++
>
> ----- Original Message -----
> From: "Edward Swynar" <gswynar@durham.net>
> To: <Gary@ka1j.com>; <amps@contesting.com>
> Sent: Wednesday, January 27, 2010 1:03 PM
> Subject: Re: [Amps] Good amp to buy
>
>
>
>> "...What do you recommend as a good HIGH power amp?"
>>
>> **********************************
>>
>> "Roll y'er own!" I say...
>>
>> The venerable, tried & true 813 is still available both new, surplus, at
>> Hamfests, etc. Two of these in parallel grounded-grid will give you
>> 600-watts output, four will up the ante to 1.2-kilowatts.
>>
>> They're practically "free", too, compared to the prices of modern 3-500Zs,
>> 8877s, etc.
>>
>> And don't let their high internal output capacitance scare you: there are
>> ways to make them play just as efficiently on 10-meters, as they do on
>> 160.
>>
>> ~73~ de Eddy VE3CUI - VE3XZ
>>
>>
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>
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