Attaching A Permanent Magnet Speaker to Model 511 Series Philcos

Model 511 Series Philco receivers were designed to use a high-impedance magnetic speaker. The original Philco speakers used some components made of pot metal, rendering many of these speaker units useless by now.

If you have one of the 211 series of metal-encased speakers, you may replace the non-functioning original with a modern permanent magnet speaker. This will give the extra added benefit of improved fidelity over the original, which had poor frequency response especially at lower frequencies.

The front of the speaker shell is attached to the rest of the case with three bayonet pins. Twist the front of the speaker shell counterclockwise slightly; the front should then come off. If it does not twist easily, try spraying inside the joint with WD-11; do not try to pry the front cover off.

Once the cover is removed, the original speaker may be unscrewed and removed from the unit. It may be replaced with an 8 inch PM speaker. Before you mount the speaker, through, be sure to mount an audio output transformer to the speaker. Even though no direct current is applied to the Philco 211 series speaker, the output transformer is important to match the low impedance of the speaker to the high impedance output of the radio.

What kind of output transformer should I use?

You need to use a single-ended audio output transformer, with an input impedance of 2000 to 4000 ohms, secondary impedance 4 or 8 ohms (depending on whether you are using a 4 ohm or 8 ohm speaker). As the 511 series sets have a low power output, a small 2 to 5 watt transformer will serve the purpose (such as Part No. P-T983 from Antique Electronic Supply).

The electrical hookup of the replacement speaker is shown below. The leads from the output transformer connect, through longer leads, to the output terminals of the 511 series radio.