Jim Barber wrote:
> Jim,
>
>
>>What experiences have people on this list had with both shielding
>>microprocessor control circuitry and display electronics internal to a power
>>amplifier from the intense RF fields as well as preventing the microprocessor
>>and display circuitry from inducing a hash onto the output signal?
>>
>>My thoughts involve a brass box, vented, with forced air cooling, that would
>>be chassis grounded, and with common-mode chokes on all leads coming from
>>this box. Would this be enough?
>>
>
> Probably, as long as a lot of common-mode RF doesn't exist on the
> cabinet in general. It would work as well as the Alphas, which is
> pretty well.
>
>
>>Also, any suggestions on which ADC/Multimeter chips that have a fast enough
>>response time as well as reasonable RF immunity?
>>
>
> Something you may want to check into is the BasicX BX-24. It has
> 10-bit ADC's, parallel IO, and a onboard multitasking OS. It's
> programmed in interpreted BASIC, but at 65000 lines/second,
> (not including ADC sampling holds) it's probably plenty fast
> enough for an amp controller. One note, tho.. The ADC's are
> ground-referenced only, so you'd probably have to use an op-amp
> to isolate the plate shunt from the ADC. Anyway:
> http://www.basicx.com
Sounds pretty good, although your choice of the 8877 is a good one also, I'm a
bit leery on using it.
I've been toying with the idea of breaking the tasks between seperate
processors, and using serial chip-to-chip networking.
I've been looking at some of the NEC 32-bit controllers myself, primarily due
to their low cost, fast speed, large I/O capability,
built-in multi-axis controllers, built-in data conversion, chip-to-chip
networking, and wide acceptance for consumer gear. I still
haven't made a final choice on the control archetecture, and as I said, I'm
open to suggestions.
The idea of using the BASIC chips would be helpful to the idea of writing an
article on this for others to build, as long as they
can program it easily. The main drawback of the NEC chips is that they are
flat-pack chips with high pin-counts, and thus hard to
work with as far as the mechanics of the soldering, although, it wouldn't be
unheard of to simply have a short-run of such boards
made and direct the reader to a source for the pre-assembled boards.
I have toyed with the idea of using the American-made[?] 8877 over the
4CX1600B, but the idea was to keep the costs down, and the
tetrode requires far less consideration on the input circuit, as well as
carries a smaller per-tube price tag. Long-term quality
and availability is also a factor. Since I don't know what the stock
conditions are on the 1600B, the 8877 could be an option if
political moves cut off the supply of 1600B's, but since it's hard to measure
the possibility of a new cold war with Russia under
current conditions, I'm continuing with the choice of the 1600B until it
appears they may no longer be available to Americans in the
future. Tube availability 5, 10, 20, even 30 and 40 years from now is a factor
in this design, and as such, the 8877 COULD end up
being a good choice for me too, regardless of the quality/price issue.
At present, the Russian tube seems the best choice because of their committment
to produce good quality, low-priced power tubes
indefinitely, which is something that I just don't see in American companies.
Remember, I'm thinking ahead here by multiple
decades. My goal is an amplifier that should last in excess of 40 years, with
little more than the need for new tubes and maybe one
or two filter-cap changouts in-between, with newly manufactured tubes still
being available that far in the future.
Even if I'm wrong about the duration of power-tube production in the United
States, I'm probably correct on the long-term quality
and pricing trends on American tubes. If this was the 1960's or 1970's, the
choice would be clear: Buy American! Since the 1980's,
American quality has gone way down, while the prices have gone way up. The
initial arguments in the electronics industry ["unions
are destroying us!"] might have been believable in 1980 and '81, but today
those arguments hold no weight with the advent of
deunionizing such shops ever since the early 80's, and the price/quality trend
has multiplied by magnitudes of order in the bad
direction, with no end in sight when it comes to declining American quality,
and ever-increasing prices. Am I being cynical, or am
I just being realistic? I tend to think the latter.
The 8877 is a good tube, but it's overpriced, and it's future availability and
quality is questionable, although current events
could end up dictating it's use in my amplifier. As a collector of old radios,
and such, I don't want to have to end up having to
get a new tube for this amplifier thirty years from now in the fashion I have
to do for some of my radios, for a large number of
tubes, it's like trading on the gold or even platinum markets, totally
unpredictable, and based on "collector value" rather than on
real value [Supply/Demand].
IMHO, domestic business decisions since the 1980's in the electronics industry
are the best argument for using Russian tubes. The
Russians have a committment to build the best, while keeping prices reasonable.
American companies just don't, they do the exact
opposite!
Even if I end up going commercial with such an amplifier, I'll probably be
using foreign parts, because I can't trust the quality of
American parts, and have no guarantees as to long-term availablity, high
quality, and reasonable pricing. Sad, huh?
This is not intended to be a political diatribe. It is intended to be a
realistic description of a decision-making process in the
initial design of a high-end amplifier, with potential commercial value,
intended to have a usable life in excess of 40-50 years.
My roomate has a sweep-tube amp using 8950's, he calls it his $150 paperweight,
and that he would have to pay someone to take off
his hands. The sad thing is that he's right. He tried selling it to me, I
said "No freaking way"!. Swan made some bad choices,
and they weren't the only one.
Business, geopolitical, and technology trends DO have to be considered at the
initial design stage of a high-end amplifier. A
high-end, modern legal-limit amplifier isn't supposed to be designed as
throwaway consumer trash, it's a long-term committment.
Trends can change, but the design must be made with forseeable events that can
effect the basic design itself. American companies
could go back to the values of my grandfather, and provide quality products at
reasonable prices again, and even pay their people a
good wage. A Cold War could happen over missiles [very easily], and effect the
availability of the Russian tubes, but until that
happens, and it may not, the Russian tubes seem to be the best decision in the
long-term.
This of course, is my opinion, and even though it is based on an objective
analysis, other people are free to differ, and there are
still good American tubes, even though their future availability, quality, and
pricing is highly questionable. The real test is of
course, to make the decision based on the best available current information,
and then wait 40 years. My decision on using the
Russian tubes is based on an American business trend that is better than 20
years old now, with no end in sight. It's no mistake
that Japan leads the radio industry today, they have a committment to quality
as well, and they have a dedicated workforce due to
the fact that they are paid a decent wage for their work, and thus take pride
in their work. Icom, Yaesu, and Kenwood don't have as
high a profit margin as American companies, but they make up for it due to the
sheer volume that gets sold because of their
high-quality.
We can do that here in America again too, but I'm cynical on if it will ever
happen. One way to start is to maybe produce the best
amplifier on the market, using well-paid American labor, and work from that
success, and that's my goal. I have no problem with
writing an article on how to build the amplifier, because I know that only a
handful of people will ever do so because the average
ham these days is an appliance operator that only memorized A, B, C, and D and
has no idea what the questions he memorized the
answers to on the test were about. Sad, but true.
Anyhow, this is starting to sound like a rant, and I want to steer clear of
such here. Like I said, I'm not knocking your choice of
tube, and I wish you the best. Thank you for the advice on the BASIC chips, I
had no idea that they had gotten that fast and
capable since their introduction, and I'll consider their use for this task, as
it could be a good idea for keeping the control
circuitry as simple as possible for the home builder.
Like I said, this is a wet-dream amplifier. I thought about building a
traditional [1930's-1950's technology] amplifier, but I
think going the extra mile is going to make a nicer one. I'm in my 30's, but
I'm a next-generation ham. It's high time that
power-amplifiers caught up with the second half of the 20th century!
jim
--
ET has one helluva sense of humor!
He's always anal-probing right-wing schizos!
-----------------------------------------------------
POWER TO THE PEOPLE!
-----------------------------------------------------
"Religious fundamentalism is the biggest threat to
international security that exists today."
United Nations Secretary General B.B.Ghali, 1995
_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|