[ARC5] C-30 missing...

[Geoff]

Subject: [ARC5] C-30 missing...


>I am curious: in the previously-hacked BC-453B I am presently working on,
> C-30, the 15 mfd 35 VDC cathode-bypass capacitor for the 12A6 audio
> output tube is missing. Apparently the original hacker removed it but 
> never
> put it back.

If its working that good why call the poor guy a hacker? Aint you got no 
respect for someone probably long departed (-;
Geez, get some single malt.......


> Even so, the audio output from this receiver is very loud. Plenty loud 
> enough
> for a loudspeaker. I am using a 600 ohm to 8 ohm transformer feeding a
> Radio Shack small 4" square CB speaker. If I turn the RF gain all the way 
> up,
> it will literally drive me out of the shack.
>
> So, is that capacitor really needed?


Not really

>
> I thought that if one removed that capacitor, some negative feedback would
> result, and the audio distortion would be reduced, but that the volume 
> would
> be reduced also.


Correct. The capacitor is there to smooth and stabilize  voltage variations 
across the cathode resistor. OTOH in a pure class A amp the variations are 
minimal but manufacturers needed bragging rights for Watts output. In an AB 
class amp its beneficial.

If I need more volume I put an electrolytic across the audio driver cathode 
in sets that have a driver. A large value if the output transformer can 
handle the lows. Ive brought distortion in some well known receivers from 
10%+ down to 2-3% and still have plenty of big speaker volume even when 
dropping the B+ down to 220-230V which keeps the 6V6/6AQ5 sets happy.


> FYI, the B+ is 240 VDC under load.
>
> I am copying an NDB, call is MW, here even in the daytime.

I can log dozens during the day on the RAK, NC-240CS, and other vintage 
commercial or military sets....with Beverages of course.


> Ken W7EKB
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