02-20-2022, 10:04 PM
An interesting thought, Terry. That would explain why there is only 1 terminal.
Philco is the only company that I have seen the "extra speaker connection" without a suitable tap on the output transformer, so your theory makes sense. However, I wonder if there was a Cost Analyst weighing ease of testing against the cost of the screw and 5.2" of #22 wire? (Length and gauge a tongue in cheek estimate.)
CDoyl, regarding replacing your original speaker with a modern PM speaker, it comes down to originality and original performance vs relative cost and possible improvement in performance. Newer speakers with better cone materials, stronger magnets and better "cone excursion" far outperform the original speakers. This may be a plus if you are going to pipe external audio through an aux jack (mp3, computer feed, etc.) The hum issue caused by replacing the field coil with a resistor (and elimination of the important hum bucking coil) can be mitigated by increasing the value of the filter capacitors, but there is a limit to this. I used to think that one can just throw in about 100 - 200 mF worth of caps in the circuit (hey, they do it on modern solid state stuff, right?) until i got the plates of the rectifier glowing red. (Oh gee, that's right, the bigger the cap, the higher the charge current drawn.) The specs of the rectifier tube in this radio do not allow for more than 30 uF as the "input cap" unless "impedence" is added in the circuit feeding the rectifier. One can likely go with 30 / 30 mF and get a low hum. One guide is to find a schematic for a similar "Post war" version of the set, as the Alnico magnets developed for the military largely replaced field coils in post war radios.
By far, the easiest route to take is to have the original speaker re-coned. I have never had this done, (I am a hacker by heart) but trust the opinion of the Pholks on the Phorum recommending that you do so.
In the meantime, you can "check out" the radio by mountig the original speaker where it belongs, and since the voice coil is now missing, connect the new speaker either across the voice coil connections of the old speaker or as I described in the previous post.
Philco is the only company that I have seen the "extra speaker connection" without a suitable tap on the output transformer, so your theory makes sense. However, I wonder if there was a Cost Analyst weighing ease of testing against the cost of the screw and 5.2" of #22 wire? (Length and gauge a tongue in cheek estimate.)
CDoyl, regarding replacing your original speaker with a modern PM speaker, it comes down to originality and original performance vs relative cost and possible improvement in performance. Newer speakers with better cone materials, stronger magnets and better "cone excursion" far outperform the original speakers. This may be a plus if you are going to pipe external audio through an aux jack (mp3, computer feed, etc.) The hum issue caused by replacing the field coil with a resistor (and elimination of the important hum bucking coil) can be mitigated by increasing the value of the filter capacitors, but there is a limit to this. I used to think that one can just throw in about 100 - 200 mF worth of caps in the circuit (hey, they do it on modern solid state stuff, right?) until i got the plates of the rectifier glowing red. (Oh gee, that's right, the bigger the cap, the higher the charge current drawn.) The specs of the rectifier tube in this radio do not allow for more than 30 uF as the "input cap" unless "impedence" is added in the circuit feeding the rectifier. One can likely go with 30 / 30 mF and get a low hum. One guide is to find a schematic for a similar "Post war" version of the set, as the Alnico magnets developed for the military largely replaced field coils in post war radios.
By far, the easiest route to take is to have the original speaker re-coned. I have never had this done, (I am a hacker by heart) but trust the opinion of the Pholks on the Phorum recommending that you do so.
In the meantime, you can "check out" the radio by mountig the original speaker where it belongs, and since the voice coil is now missing, connect the new speaker either across the voice coil connections of the old speaker or as I described in the previous post.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55
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