10-29-2016, 12:11 PM
Terry (Radioroslyn), I appreciate you...but I must disagree on using a PM speaker.
Using a PM speaker means that you must come up with a way to replace that 660 ohm field coil. Sure, a resistor can do the job...but it will also create lots of heat. The 38-5 uses eight tubes and that means a sizeable amount of current flowing through the speaker field (or resistor) which translates to plenty of heat dissipation if a resistor is used.
There are ways of getting around the need of a K-39. The same Excel spreadsheet also gives the specs of other 8 inch Philco speakers with 660 ohm field coils. There's the K-23 (19B, 144B) and K-34 (37-640B) as examples. Yes, you will have to replace the audio output transformer if you use a K-23, but if the transformer mounted on your current 10-1/2 inch speaker is good, you could remove it from the large speaker and mount it on the smaller one. A K-34's specs are close enough to a K-39 that it could serve as a direct replacement including output transformer.
You could even be really radical and remove the field and pot from your 10-1/2 inch speaker and mount it on the frame of a Philco K series speaker frame (not an S, but a K). But I would not recommend that to anyone but more advanced collectors with plenty of experience in repairing and restoring old radios.
I would only use a PM speaker and resistor as a last resort.
Using a PM speaker means that you must come up with a way to replace that 660 ohm field coil. Sure, a resistor can do the job...but it will also create lots of heat. The 38-5 uses eight tubes and that means a sizeable amount of current flowing through the speaker field (or resistor) which translates to plenty of heat dissipation if a resistor is used.
There are ways of getting around the need of a K-39. The same Excel spreadsheet also gives the specs of other 8 inch Philco speakers with 660 ohm field coils. There's the K-23 (19B, 144B) and K-34 (37-640B) as examples. Yes, you will have to replace the audio output transformer if you use a K-23, but if the transformer mounted on your current 10-1/2 inch speaker is good, you could remove it from the large speaker and mount it on the smaller one. A K-34's specs are close enough to a K-39 that it could serve as a direct replacement including output transformer.
You could even be really radical and remove the field and pot from your 10-1/2 inch speaker and mount it on the frame of a Philco K series speaker frame (not an S, but a K). But I would not recommend that to anyone but more advanced collectors with plenty of experience in repairing and restoring old radios.
I would only use a PM speaker and resistor as a last resort.
--
Ron Ramirez
Ferdinand IN
