[AMRadio] Re: Need list of good AM radios to start looking for .


Rbethman rbethman at comcast.net
Wed Nov 16 15:25:43 EST 2005


Folks,

Go to the AM Window site.

Under DX-60 mods (WC3K), you'll find a modulation mod to monitor 
exceeding 100%.  VERY easy to do, AND inexpensive.  IF the led flashes, 
you are exceeding 100%.  This is a beautiful mod, and Bill used the LED 
in lieu of a front panel screw.  Completely reversible, and NO extra 
holes in the panel.

Bob - N0DGN

W5OMR/Geoff wrote:

> Jim candela wrote:
>
>> Dan,
>>
>>    I like your suggestion. I never tried it, so I am no authority on 
>> this
>> modification. In general, this would change the modulator load 
>> impedance,
>> and the RF pi network formulas would suggest juggling the L/C ratio to
>> maintain the same 'Q'. I might be tempted to use some sort of 
>> negative cycle
>> loading to contain the modulator, and minimize splatter by keeping the
>> negative modulation below 100%, and letting the positive peaks fly 
>> upward
>> beyond 100%. Doing this however may raise the PEP drive power too 
>> high for
>> the linear, so that's another issue to contend with. Running both 
>> modulator
>> and final RF stage at reduced B+ may still be the best approach when 
>> driving
>> an amplifier with low drive requirements. Another option is to use 
>> the 2e26
>> and low B+ for really low drive amplifiers.
>>
>
> The reason the 2E26 was suggested (I've heard it several times, 
> m'self) is that it requires exactly the same B+, screen voltage, grid 
> voltage and everything else that the 6146 does.  The 2E26 just has 
> half of the plate dissapation.
>
> Therefore, ass/u/me'ing 600V for B+, and half the current (50mA vs 
> 100mA in the 6146) the final impedance changes from 6000 ohms to 
> 12,000 ohms.  You would think that it would be easier for the 
> modulators to work into a higher impedance range.
>
> I like the idea of using the 300 or so Low Voltage supply on the 
> final, but I think for audio sake, I'd leave the B+ up on the 
> 6L6/1614/7027's
>
> 300v @ 50mA would still be 6k ohms of Z in the final.
> (not to mention half of the current being consumed by the modulation 
> transformer secondary, and therefore further away from saturtion)
>
> As for keeping the audio at a 'tame' level, there is no better tool 
> for operating AM than a good O'scope because (as Don Chester/K4KYV has 
> often said)"
> "Operating your AM rig without an O'scope, is like driving you car at 
> night, without headlights."
>
> ---
> 73 = Best Regards,
> -Geoff/W5OMR
>
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>

-- 
Bob - NØDGN
                       
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