So today's primary task was to prep the speaker panel...and, yes, I know it is just plywood and won't be seen but it got sanded (both sides, edges, and around the hole). I will either seal the face with poly or paint before covering with cloth, and the back will get stained to match the interior and poly'd.
Now for some questions...
1. Do I use some rubber washers to "float" the speaker on the board or mount it firmly to get some "subwoofer resonance" from the panel too?
2. As you can see, I removed the broken cone and planned to sell/donate the Field Coil basket but...
a. How available are replacement cones for this speaker?
b. Is it a DIY effort to glue it in and wire it?
c. Can I test it "externally" and, if so, what kind of power source does it need and can you feed it a Red/Black from a stereo amp? It has a 3-pin plug.
A good source to get speakers reconed and voice coils replaced is Sound Remedy in NJ. His email is
soundremedy@aol.com
I'd give you the website but my antivirus is currently blocking it as bad so I would simply email him for prices, timing etc. A number of folks here on the Phorum have used him successfully.
I'm not the best guy to give advice on speakers but I'm not quite sure what you are trying to do. If you want to use the original speaker but without the field coil I think it will be difficult to make it work properly. Based on the picture in the For Sale section it appears the spider on the voice coil is damaged as well as the cone. The field coil provides the magnetic field that the voice coil operates within. Without the magnetic field you would have to add a permanent magnet somehow and getting the right set up might be difficult. If you are not going to use the original radio chassis anyway I would just put in a modern speaker of the approximate size you need and be done with it. If I'm misunderstanding things just let me know.
If the "spider" is the paper swirl with 3 "tabs", two of them were torn when I got it. Based on photos I've seen, I considered it part (tip) of the "cone". There's a small center bolt that connect the "cone" to the floating "coil" inside the electro-magnet coil.
I'd like to use the audio transformer and field coil with the repaired cone but I don't know exactly how the main chassis gets both power and signal to it via the 3-pin connector. Then I could rig up a "test connector" and "drive" the speaker separate from the chassis. I'll squint harder at the schematic.
I may end up back at my initial decision to just sell what I have and put in a modern mid-range (and tweeter?) but I wanted to check my options for reusing more of the existing stuff. Goodwill, Salvation Army, and Garage Sales are my main "suppliers".
(This post was last modified: 03-02-2023, 12:55 AM by DavidK.)
David, your might want to take a slower and more cautious approach to your project. Your speaker field coil gets it's energy by being wired into the power supply filter circuit where it performs double duty. It is a filter choke coil reducing the ripple on the high voltage DC supply and it provides the magnetic field for the speaker voice coil. Since one wire of the field coil is B+ and one wire of the output transformer is connected to B+ there is only three wires required to operate the speaker. It's not always evident when looking at the schematic but you should be able to trace it. The main thing to be cautious about is the B+ voltage is a couple hundred volts and it's on a wire external from the chassis. Potentially hazardous (tongue in cheek). Nice strip job on the cabinet. Please don't use polyurethane. IMHO, I much prefer lacquer and for darker areas I like to stain rather than lacquer tinting. Thanks for showing us your progress.
Thanks, Rod! Yes, my wife says I have two speeds: Off and Full Throttle.
I've see some of those cap ratings and it does look like Darwin's Theories could quickly thin me from the herd. Hanging onto the suspended power cord over my father's workbench when the plug end came off was a "unique" feeling (as a young lad). But 110 AC is at least nice enough to cycle phases and give your muscle a brief chance to let go. I believe DC is NOT that "forgiving". A friend of mine who has some EE background tried to remind me of the "One hand in your pocket at all times." rule, but I had never heard that before...yet I sort of understand what it means.
I've probed the big black transformer (separated from the chassis) and found something like 400 VAC, 5.6 VAC, and 7.8 VAC. According to the Parts Catalog from 1939 it should be 636, 5.0, and 6.7 so is this "drift" a sign of age/degradation? The 5.6 at least lets me see my replacement 6.3 V dial bulb light up. The schematic I've seen only have resistance values (as far as I can tell).
But, I think what you are telling me is that (with some internal/tube "magic") the Audio Signal (red/black to me) is "interleaved" in two different "input" voltage pins and the other "return" ground pin? I was thinking these would be AC on the wires from the main chassis to the speaker and then split/transformed on the "basket".
Hello David, it's me again. I also wanted to comment about the rubber grommets for mounting the speaker. Unless you have a specific reason to use them, don't. You have a nice plywood baffle to mount the speaker on and the only moving object should be the speaker cone/voice coil. The cone is pushing air and the baffle is there to prevent the air at the back of the cone from trying to cancel the air movement on the front. If you use rubber mounts they may absorb some of the cone movement or provide an acoustical leak around the edge of the speaker. Now some people tweak their speaker drivers to do this but for our purposes we're not looking for fidelity on an AM radio, just nice sounding sound. No buzzes or dead spots. Some have experimented with mounting a back on the cabinet to completely or partially box in the speaker. And I've seen elaborate acoustical wave labyrinth systems made by the manufacturer to get everything out of the speaker. Probably more of a marketing gimmick than anything.
Super information! Thanks again! It helps me consider some of the physics involved here (re: air movement). So (now that my mind is racing) do we want the cone to basically "eject" a wave of air (creating a pseudo vacuum inside the cone), and then does it suck air back into the cone chamber around the circumference?
>I've probed the big black transformer (separated from the chassis) and found something like 400 VAC, 5.6 VAC, and 7.8 VAC. According to the Parts Catalog from 1939 it should be 636, 5.0, and 6.7 so is this "drift" a sign of age/degradation? The 5.6 at least lets me see my replacement 6.3 V dial bulb light up. The schematic I've seen only have resistance values (as far as I can tell).<
For those following at home here's the diagram: https://philcoradio.com/library/download...l.%202.pdf Typically transformers don't drift like resistors or caps they short from overload. If the voltages are somewhat high it can be explained by higher line voltage and perhaps not having any tubes installed when testing. The 400vac measurement was that from chassis one plate and the other? Or from plate to plate? If it's from plate to plate that's a little concerning. Check the resistances midpoint (transformer center tap) to each end of the high voltage winding. The two reading should be within about 10-15% of each other. If way different the winding is shorted and transformer is scrap.
Never try to operate the set with the spkr unplugged or the hv filter caps not replaced. Doing so is asking a lot of trouble! You can however remove the 5Y4 tube and check things out just there won't be any hv. Also check the primary of the output transformer. Not uncommon for it to be open (reading in the 20K or more). Should see a few hundred ohms.
GL w/your project!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Speaker cone: yes, but the vacuum is off the back of the cone. So if your baffle is infinitely large the cone is most efficient.
Power transformer: it sounds like it has been removed from the chassis. You may be measuring the 400 volts across one side of the high voltage winding. The high voltage winding has a center tap. If you measure the end-to-end voltage out of circuit it could measure 750-780 volts. You should have three wires for the hv winding, one is the center tap. Between center tap and each end you should read 350-375 volts. The 5 volt winding is for the 5Y4 rectifier filament and the 7 volt winding is for the filaments of the rest of the tubes and pilot light. Under load the voltages should be measuring around normal or slightly higher. Mike was concerned that the 400 you measured is too low. If you report back that it was one side of the hv winding then it should be OK.
Aha! Now that I understand about CT transformers and paid closer attention to the faded/yellowed wires, it makes more sense. [A section of the casing on the CT wire is broken and wire is exposed...not a good sign. Old stuff is so brittle!] I had a CT reading before...or misread my analog meter. Across the full coil I get about 180 (times 4 for the 1000 V range setting) I see 720 (which is better...and scares the out of me). All of my readings were taken at the end of the wires that directly feed into the transformer.
This may be a live (hopefully) and learn experience.
David, just to reinforce what Rod mentioned about dangerous potentials on those speaker wires, it reminds me of a time in my teens. I was just getting interested in electronics and being a dumb kid messing around with an old radio a friend and I found at the curb back in the 60s. I really had no business doing what we did, a little knowledge can be dangerous we pulled the chassis and speaker from the cabinet and put it on a table. We had it turned on and my friend had his arm laying across the speaker while at the same time went and tried turning up the volume by grasping the bare metal volume control shaft. Well it picked him up and threw him up against the wall. Now in hind sight I know why. His arm was in contact with one of the DC high voltage terminals on the speaker and when he touched the metal control shaft which was at B-, he was hit with fully around 300V, luckily he wasn’t electrocuted! Dangerous stuff for a couple of wet behind the ears kids!
Sorry about that. I think I had two threads going with the same "Subject" line but each in their own forum to discuss different aspects (cabinet vs electronics), but I see how that could be confusing if just looking at "all threads". I'll make sure the Subject is more clear.
Hanging onto the suspended power cord over my father's workbench when the plug end came off was a "unique" feeling (as a young lad). But 110 AC is at least nice enough to cycle phases and give your muscle a brief chance to let go. I believe DC is NOT that "forgiving". 
A friend of mine who has some EE background tried to remind me of the "One hand in your pocket at all times." rule, but I had never heard that before...yet I sort of understand what it means. 
out of me). All of my readings were taken at the end of the wires that directly feed into the transformer.
we pulled the chassis and speaker from the cabinet and put it on a table. We had it turned on and my friend had his arm laying across the speaker while at the same time went and tried turning up the volume by grasping the bare metal volume control shaft. Well it picked him up and threw him up against the wall. Now in hind sight I know why. His arm was in contact with one of the DC high voltage terminals on the speaker and when he touched the metal control shaft which was at B-, he was hit with fully around 300V, luckily he wasn’t electrocuted! Dangerous stuff for a couple of wet behind the ears kids!
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