[AMRadio] stock or mod

W5OMR/Geoff 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 
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!
>> 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! 

What other hobby lets you have -this- much fun?  :-)

73 = Best Regards,

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