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Restoring a Philco 41-629 - Printable Version

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Restoring a Philco 41-629 - TomBoy - 08-27-2018

Hi,
I am a new member of the Philco Phorum and I am pleased to have discovered this website.

I have replaced all of the electrolytic capacitors and all of the wax/paper capacitors. In addition I replaced any resistors that had drifted out of tolerance. I also discovered that the primary of the output transformer had been previously burned out. So the output transformer has also been replaced. Then I peaked all of the IF coils and antenna/RF circuits.

The AM band works quite well and has good sensitivity.
However, on the SW band (8.9 to 12 MHz) all I get is a loud hum - almost like motorboating. It is not 60 Hz or 120 Hz power supply hum as the B+ is nearly ripple free. The noise seems to have peaks and valleys evenly spaced along the SW band. Any Ideas on what is causing this and how to cure it?

Also, should the local oscillator frequency be set above the desired station frequency or below it? Currently it seems that the local oscillator for the SW band is operating below the desired station frequency.
Any help and advice will be greatly appreciated.

RE: Restoring a Philco 41-629 - Radioroslyn - 08-27-2018

Hi Tom and welcome,

> Any Ideas on what is causing this and how to cure it?
Probably interference from some modern electrical device like a battery charger or computer. Unplug the offending device. In some cases ground may help but it's a roll of the dice.

>should the local oscillator frequency be set above the desired station frequency or below it?
On most sets Philco and others it's above the incoming signal. On some communications receivers it's below on the higher frequency band, + 25mc.

RE: Restoring a Philco 41-629 - TomBoy - 08-27-2018

Thanks for the quick reply. I have found that the noise is worse or better depending in which receptacle I have plugged the cord into. Then I plugged the Philco into a special receptacle that has a Cornell Dublier EMI filter installed and that seemed to help. However that did not totally solve the problem.

By the way, when I replaced the power cord, I used a 3 wire grounded cord and the ground pin wire has been connected to the chassis.

On the AM band I have the local oscillator above the station frequency.  Perhaps I will try to tune the LO for the SW band above the station frequency as well. However, it probably should not make a difference.

RE: Restoring a Philco 41-629 - Paul Philco322 - 08-27-2018

Looks like you did a super cleanup and resto job. I am always chasing interference, I blame my neighbors! My washer and my furnace are sometimes to blame. 

Paul

RE: Restoring a Philco 41-629 - TomBoy - 08-27-2018

Thanks. I am retired so I have time to pay attention to detail.

RE: Restoring a Philco 41-629 - Radioroslyn - 08-29-2018

Nice looking set!

Using the ground via the outlet may increase the interference level as the interference is on the hot and neutral power leads. All three wires are in very close proximity to each other. Electrically speaking the wiring looks like a large capacitor coupling the interference from the hot and neutral wires to the ground wire.
You might try using an adapter (3 pin to 2pin) so the the ground connection is not connected. This may help or connect a different ground to the radio's chassis. Cold water pipe or if you have hot water baseboard heat the baseboard element is good.

RE: Restoring a Philco 41-629 - TomBoy - 08-29-2018

Thanks. I will give the separate ground connection a try.