Todd, KA1KAQ wrote:
The one rig that -needs- the most modifications to better the
enjoyment of this particular peice of equipment, is the 75A series of
recievers. In particular, the 75A-4, and I'm not sure that enough can
be done to that reciever to bring it to be nearly as good as a
properly aligned phase-shift receiver.
Rather than trying to re-design or rebuild the 75A-4 into something
it was never meant to be, I prefer the other alternative: get another
cool radio! Of course, I paid a fraction of the going epay-high price
for mine or I wouldn't even be able to comment from experience. Seems
like a lot of folks have paid big bucks for them because someone said
they should.
That's my thoughts. I think the 75A-4's price is artifically inflated.
They weren't/aren't -that- good of a reciever.
Another 'good' mod (at least one that's acceptable by the 'in' crowd,
for a KW-1, would be to change out the 4-400's in the final, for
4-250's. The 810's would work better into those jugs, I think, as
opposed to the 4-400's.
These, of course, are my personal opinions.
I looked into this many years ago and even picked up some 4-400Cs just
for that reason. Electrically I believe they work a lot better,
loafing along. The downside is: virtually no purty-red glow.
In Class C, tha'ts a -good- thing :) If you wanna see color, bias the
modulator off about 50 to 100w above the dissapatoin level. (ie:
250TH's have 250w of dissapatoin. I run 2800v @ around 125mA of bias.
A dull orange glow, but a glow, none-the-less)
I suppose that just because you can run a pair of 4-1000's in the
final, doesn't mean you're gonna slap 4kVDC to the anodes, and load 'em
up for 1000mA of plate current. 1500VDC @ 400mA is a good round number,
for DC power input.
4-400's instead of 4-125's or 4-250's, for the same power out as the
4-125's would certainly have plenty of 'head room' to be completely, and
fully modulated.
Paul does bring up an interesting point, too: roughly halfway through
production the engineers (supposedly on Art's orders, but who knows
now?) restricted the audio response further to give the transmitter
more punch. Which design is correct or better? That's a matter of
taste and opinion. I changed one resistor and one or two caps in mine
when I first got it on the air back in August of 1990. Also bypassed
the clipper, splatter choke, and changed the taps on the mod iron.
Simple stuff that made a very noticable difference, and I sleep just
fine at night.
Speculaton on my part says:
Back in those days, SSB was coming in, and band-space was a 'premium'.
More restrictive audio, less fidelity, the result was that there was
less of a 'foot-print' that the signal took. Orders from Art?
Probably. Where did Art get his direction? Certainly there were
lobbyists then, as well. Politics has been around longer than I care to
think about.
>We, as the Providers of Good Homes when these transmitters reach
private hands then have to decide whether to "restore" an already
modified transmitter back to original, or functionally bring it up to
the application where it can best be used.
>
I prefer the latter. Just because it 'could' be a museum peice, doesn't
mean it 'has' to. It was designed to 'work', by golly, WORK IT!
EXACTLY!
the idea of 'buying' a show-peice of equipment, and then not using it
because you don't want to damage it is counter-productive to the
activity of Ham Radio, in general, and not just the Boat-anchor crowd.
Yep, it makes good sense. Use it, have fun. If it breaks, fix it.
Rick is modifying a braodcast transmitter for use on the ham bands. Good
for him! Bob is gonna xtal-ing up an old CB for use on the ham bands.
horray! BC-610's are used on frequencies other than military
issued/controlled. Does that mean that they're operating out of their
specifications? Military Boatanchor General Coverage recievers... well,
goodness me! They're not tuned to a military RTTY frequency, rather
instead they're copying (*gasp*) AM Transmissoins on 75m? Oh, the
Horror! Is the world gonna come to an end? The Sky is falling, the SKY
is falling!
</sarcasm>
What other hobby lets you have -this- much fun? :-)
--
73 = Best Regards,
-Geoff/W5OMR
