[NJARC] The HUMMM on my Philco 116X...

[Jim Whartenby]

________________________________
 From: Jim Whartenby <antqradio at sbcglobal.net>
To: njarc at mailman.qth.net
Sent: Thursday, July 11, 2013 1:39 PM
Subject: Re: [NJARC] The HUMMM on my Philco 116X...
 


There are trade offs in using a higher then original value filter capacitor.  The main problem is a higher charging current that comes with using the higher value capacitor.  This will cause the rectifier to have to work harder and shorten it's working life.  The higher charging current should also cause the power transformer to operate at a higher temperature.  More current with the same winding resistance is more waste heat.  So you get to stress two components for the pleasure of reducing hum.

Hum is also a byproduct of electrodynamic loudspeakers.  The field coil is as an electromagnet.  It is also used as the filter inductor in the power supply.  So the magnetic field is injecting hum directly into the loudspeaker.  To reduce this hum, there is a hum bucking winding which intentionally adds hum but 180 degrees out of phase to the power supply filter inductor.  This is not perfect cancellation so some hum is always present.

Not everyone bothers to listen to the noise between radio channels so the hum is usually drowned out by the program information.  This used to be music but now more often political commentary on the BCB or religious commentary on the short wave bands.

Sad, as a youth using an Atwater Kent Model 70 TRF set, I use to enjoy Cousin Brucy while in the basement learning the black art of electronics.  TRFs have an impressive dynamic range and no hiss from mixing.  Lots of fond memories of what came out of that old radio.
Jim


________________________________
 From: "sgt88 at atlanticbb.net" <sgt88 at atlanticbb.net>
To: njarc at mailman.qth.net 
Sent: Thursday, July 11, 2013 12:14 PM
Subject: [NJARC] The HUMMM on my Philco 116X...
 

Just remember
Reply = Poster
Reply All = Everyone

_________________________________________________________
..is higher than I'd expect after changing out ALL the caps.

There is this "potentiometer" to minimize the hum
 between the 6A3's finals for matching...it's miminized.

I've only really heard one other old console..my Philco 37-620..which sounds OK.

Sooooooo...is hum to be expected??...or should I replace the electro's with higher value 'farads'?

The hum is not really noticeable with a station tuned in...

Tnx,
Steve T.
______________________________________________________________
NJARC mailing list
Home: http://mailman.qth.net/mailman/listinfo/njarc
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:NJARC at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html