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


W5OMR/Geoff w5omr at satx.rr.com
Wed Nov 16 15:20:29 EST 2005


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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