On Thu, 02 Mar 2006 00:51:43 -0500, Larry wrote:


http://hawkins.pair.com/wabcnow/wabcn14.jpg

That little board puts out 1KW with 240VDC applied...

Do they put 50 boards in parallel?

In article ,
Larry wrote:

Bruce in Alaska wrote in news:bruceg-
:

I even remember when we used 866A's in the Power supplies, as
Recitifiers.



Yecch.....flashovers! Been there, done that....

Bruce, have you seen what an AM transmitter looks like, now? A 50KW AM
broadcast transmitter uses POWERTAB transistors for final output stages!

http://hawkins.pair.com/wabcnow/wabcn14.jpg

That little board puts out 1KW with 240VDC applied...

Amazing. A 50KW broadcast transmitter cooled with muffin fans....55KW from
the power company...50KW to the antenna!


No, i really haven't kept up on Broadcast Engineering, since I left that
field in the late 60's, in a previous life. I understandf that some of
the newer Transmitters using Class D & E Amps are very efficent and
compact in the extreme, compared to what I was working with.

Bruce in alaska
--
add a 2 before @

In article ,
"Lynn Coffelt" wrote:

I enjoyed your Peeair story, Bruce, I know Don must be rolling over in the
grave. (I did like Don's little active (Dymek?) antenna, though, to get the
WEFAX antenna up and away from the digital noise disaster in the pilot
house)

Old Chief Lynn

Yea, Don was one hell of a smart guy, and one World Class Radio
Designer, for his day. I think I still have a Stoner CB around here
somewhere.
Lynn, would you know if Finn Christensen is still working for SGC.
He was the guy who did the orginal design of the N571-575 series
Poweramps, and left Northen just before it was bought by that Guy
from California and moved to Redmond. He went to SGC to help PeeAir
figure out how to build a SS PA for the follow on SSB Radios after the
711.
I kind of lost track of him after Northen went under, and I saw him at
the Bankrupcy Auction.

Bruce in alaska
--
add a 2 before @

"Bruce in Alaska" wrote in message
...
In article ,
"Lynn Coffelt" wrote:

I enjoyed your Peeair story, Bruce, I know Don must be rolling over in
the
grave. (I did like Don's little active (Dymek?) antenna, though, to get
the
WEFAX antenna up and away from the digital noise disaster in the pilot
house)

Old Chief Lynn

Yea, Don was one hell of a smart guy, and one World Class Radio
Designer, for his day. I think I still have a Stoner CB around here
somewhere.
Lynn, would you know if Finn Christensen is still working for SGC.
He was the guy who did the orginal design of the N571-575 series
Poweramps, and left Northen just before it was bought by that Guy
from California and moved to Redmond. He went to SGC to help PeeAir
figure out how to build a SS PA for the follow on SSB Radios after the
711.
I kind of lost track of him after Northen went under, and I saw him at
the Bankrupcy Auction.

Bruce in alaska
--
No, I am not familiar with Finn. I really only know Pierre from
telephone conversations. He would make a sales pitch call once in a while.
And I'd have to try to be polite.

There was a nice 100' Knight-Carver (or was it Carver-Knight?) here
with two of the latest and greatest SGC 24 channel synthesized rigs here.
Owner's full time maintainer said factory techs had installed and tuned them
down in San Diego. One of them worked fairly well, but the other barely
hailed vessels in the same marina. Super Tech, Old Chief Lynn was called
into action. The poor performer's little square box manual tuner was at arms
length in a console cavity. When I finally got the lid off the little
bugger, the tuning jumpers and capacitors were still untouched in their
little plastic bags. Sheesh!

I'm slowly gathering dusty parts for an 866A lit power supply...... I'm
without a rig right now, and never had a store boughten transmitter yet.
Itching to get back on 40 CW before I forget the code. (or there are no CW
operators there).

(is this thread, "30amp 12v circuit", something for filament power?)

Old Chief Lynn

Wayne.B wrote in
:

Do they put 50 boards in parallel?




No, it actually has something like 248 boards, in parallel. There is one
board that always puts out 100 watts, the only board turned on at the
negative 100% modulation peak. The other boards are controlled by a long
driver board mounted outside the RF shield and hooked to them with big
ribbon cables. The modulation audio simply turns all but the one on and
off as the audio waveform is converted to the digital data. With no
modulation, half the boards produce a 50KW output carrier. As the audio
waveform goes up, more boards switch in up to 100% modulation peak, then
back to half and down to only the one 100W output, then back up. The
output amounts to a sum of all these boards' square wave switching
output. The big square wave is sent to a tuned circuit that filters out
the harmonics with more low-pass filters to keep the neighbors happy.
The output, of course, is an amplitude modulated sinewave that is quite
smooth, considering it comes from a digitized square wave. Being
actually a switching power supply at the RF carrier frequency, the boards
are 95+% efficient like the power supply in your computer....making the
company VERY happy as the electric bill comes down from 130KW load, the
rest wasted as heat, to 55KW load with only 5KW of heat coming off with
simple cooling fans. Simply amazing switcher technology, considering
AM's analog roots. Harris has a pretty good lock on the market for AM
transmitters, now.

The boards come in 100W, 200W, 500W and 1KW power levels, I think.
Binary switching them as the audio waveform is digitized makes quite
small power steps hardly recognizable in the modulated output.

Listen to almost any clear channel AM station in the USA and you'll be
listening to a Harris DX-50 these days. Hell, WWL on 870Khz was on the
air through the hurricane with theirs....near New Orleans.

On Fri, 03 Mar 2006 12:59:23 -0500, Larry wrote:

Being
actually a switching power supply at the RF carrier frequency, the boards
are 95+% efficient like the power supply in your computer.

Interesting, I had no idea that AM transmitter technology had gotten
that sophisticated. Makes sense though. Unfortunately I can't see
much applicability to the SSB world, or to reduced carrier AM.

In article ,
Larry wrote:

"Lynn Coffelt" wrote in news:du8kc5$k1$1
@emma.aioe.org:

(is this thread, "30amp 12v circuit", something for filament
power?)


30 amps? REAL filaments won't even glow at 30 amps!....(c;

If you'd like them, I have pdf files of the '63 RCA Power Tube
Guide, '52 Eimac Broadcasters Tube Catalog, and some other
interesting old ebooks I've collected. They're too big to email
but I can setup a virtual FTP server for ya, chief.

600KW of CW on 40 meters will reach out and touch someone...(c;


600Kw on 40 Meters has the ability to reach out and touch the operator,
if he should get to close to the RF Ammeter.....

Bruce in alaska
--
add a 2 before @