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Get familiar with the reaction system: Introducing the Reaction System
Vintage "Field Coil" Loudspeaker (1932)
My sister asked me to take a look at her father in-law's vintage (1932) Philco Model 90 Lowboy. This is a floor standing AM radio from the early 30's that uses 9 tubes and has a large 11 inch diameter full-range loudspeaker mounted in the lower half of the cabinet (see pics below). The loudspeaker does not use a permanent magnet. Instead, it has what is called a "field & bucking coil." The field coil is energized by the radio's high voltage B+ power supply and functions as an electromagnet in the voice coil gap.
The loudspeaker's voice coil/cone/spider assembly is very stiff due to age. Pushing very hard on the cone results in almost no deflection at all. Careful disassembly and replacement is therefore needed. The service data spec sheet from 1932 lists this as "Voice Coil Assembly and Cone" part number 02997 available at a net price of US 60 cents each. I checked ebay for a Philco NOS 02997 cone assembly, but none were available with a buy-it-now price of 60 cents (ha ha ha!).
If available, replacement would be a simply matter of removing 9 bolts, de-soldering the two voice coil wires, and then lifting the entire cone and voice coil assembly out and away.
Replacing the surround would be fairly easy using a standard PE re-foaming kit. But replacing the stiff spiral spider would be difficult. I checked some threads on the philcorepairbench.com web site forum and discovered that I would have to very carefully remove the spider from the VC and then trace out a template on a piece of paper. Then I would need to find some thin fiber or plastic type material of just the right flexibility to make a new spider. This is critical, because when I glue the replacement spider back onto the VC and re-assemble the speaker, the original Fs, Q, and tonal quality must be restored. If I error on the side of too flexible, then the speaker cone might bottom out or "pop" at higher volume levels. If I make it too stiff, the rich, deep bass tonal quality will suffer.
Other problems: This radio is in very bad shape and needs to be completely re-wired, re-capped and re-aligned. It has been repaired and modified, in a very sloppy manner, several times over the years. Some of the repairs were hacked into place by soldering several replacement parts end to end with absolutely no support. In many places interconnected parts have been left dangling in mid air, supported by nothing more than their own thin leads! (see pic below).
I would estimate 40+ hours and $100+ in parts to restore, if I did the work myself. I checked the cost of several non-local vendors that are willing to do this kind of restoration and discovered that sending it out for repair would probably run $600 to $800 plus shipping, plus an additional $100 hacking surcharge.
My plan, therefore, is to simply return the radio to my sister as is. Maybe she can re-finish the cabinet and then set it in their living room as a show piece. I'll make sure that someone cuts the power cord off so that no one accidentally plugs it in and burns the house down! (smile) Thoughts?
Bill
The loudspeaker's voice coil/cone/spider assembly is very stiff due to age. Pushing very hard on the cone results in almost no deflection at all. Careful disassembly and replacement is therefore needed. The service data spec sheet from 1932 lists this as "Voice Coil Assembly and Cone" part number 02997 available at a net price of US 60 cents each. I checked ebay for a Philco NOS 02997 cone assembly, but none were available with a buy-it-now price of 60 cents (ha ha ha!).
If available, replacement would be a simply matter of removing 9 bolts, de-soldering the two voice coil wires, and then lifting the entire cone and voice coil assembly out and away.Replacing the surround would be fairly easy using a standard PE re-foaming kit. But replacing the stiff spiral spider would be difficult. I checked some threads on the philcorepairbench.com web site forum and discovered that I would have to very carefully remove the spider from the VC and then trace out a template on a piece of paper. Then I would need to find some thin fiber or plastic type material of just the right flexibility to make a new spider. This is critical, because when I glue the replacement spider back onto the VC and re-assemble the speaker, the original Fs, Q, and tonal quality must be restored. If I error on the side of too flexible, then the speaker cone might bottom out or "pop" at higher volume levels. If I make it too stiff, the rich, deep bass tonal quality will suffer.
Other problems: This radio is in very bad shape and needs to be completely re-wired, re-capped and re-aligned. It has been repaired and modified, in a very sloppy manner, several times over the years. Some of the repairs were hacked into place by soldering several replacement parts end to end with absolutely no support. In many places interconnected parts have been left dangling in mid air, supported by nothing more than their own thin leads! (see pic below).
I would estimate 40+ hours and $100+ in parts to restore, if I did the work myself. I checked the cost of several non-local vendors that are willing to do this kind of restoration and discovered that sending it out for repair would probably run $600 to $800 plus shipping, plus an additional $100 hacking surcharge.
My plan, therefore, is to simply return the radio to my sister as is. Maybe she can re-finish the cabinet and then set it in their living room as a show piece. I'll make sure that someone cuts the power cord off so that no one accidentally plugs it in and burns the house down! (smile) Thoughts?
Bill
Comments
a few more pics
a few more pics
You're right, it doesn't look too bad from this distance. I'll snap and post a few macros next week. Lots of crystalized, cold solder joints, parts hanging in mid air, etc.