[Amps] Good amp to buy

Sun Jan 31 16:25:59 PST 2010


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 at durham.net>
> To: <Gary at ka1j.com>; <amps at 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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