|[AMRadio] stock or mod|
w5omr at satx.rr.com
Tue May 30 15:31:35 EDT 2006
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
> 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
>> >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!
>> 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
What other hobby lets you have -this- much fun? :-)
73 = Best Regards,
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