4x6 Speaker Question for 42-345 - Printable Version
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4x6 Speaker Question for 42-345 - cdoyal - 02-07-2022
Does anyone have any suggestions for an alternative to the 36-1543-9 in this set? Field coil measure 1600 ohms. No idea how many ohms the speaker is. Voice coil and cone are toast.
Thanks!
RE: 4x6 Speaker Question for 42-345 - MrFixr55 - 02-07-2022
Hi Cdoyal,
What model radio does this speaker come from? I am assuming that this is late pre-war or early post war (War being WWII).
A few suggestions:
You are not going to really harm anything by using an 8 Ohm Speaker, although I am going to hazard a wild guess that this is between 3.2 and 4 Ohm.
If you are trying to keep the radio original, there are several speaker rebuilders that some of the forum experts can recommend.
If you don't care about originality, you can install a modern speaker (available at Pep Boys, eBay, etc.) and either:
- Substitute a 1600 Ohm 5 or 10 Watt resistor for the
Field coil and replace the electrolytics with 40 MFD.
- Lop off the field coil and magnet assembly from the
speaker and find a semi-pretty way to enclose and
mount it.
Hope this helps.
Best Regards,
John MrFixr55
RE: 4x6 Speaker Question for 42-345 - MrFixr55 - 02-07-2022
Oops, OK that is the model, 42-345
Radio must be pretty compact. I have never seen one of these, but the Schematic is available on Nostalgia Air. Typical Philco, the tubes are out of a car radio, including the rectifier. This is not a bad thing. This should be a fairly nice radio. A modern 4X6 speaker would sound better than the original.
RE: 4x6 Speaker Question for 42-345 - cdoyal - 02-08-2022
Thanks John. That's very helpful. If I were to replace it with a modern 4x6, where would I attach the leads? (I'm not super savvy with this stuff. Yet.)
RE: 4x6 Speaker Question for 42-345 - MrFixr55 - 02-09-2022
Hi Cdoyl, If "not yet", you will get there!
I am way too wordy, but please read through the entire post and take the advice of any "Expert" that posts.
The instructions below are given assuming that you have a schematic diagram and can recognize the parts described. These instructions are also based on you having either "recapped" the radio or that the radio successfully functioned. If you have obtained this radio in original, unrepaired condition, then do not power up this radio until all electrolytic caps have been replaced. In fact, all capacitors, including all of the "wax paper" caps should be replaced. Failure to do so can cause failure of other parts, especially transformers and may cause a fire!
There are many good threads and articles on recapping, especially on this "Phorum" If you have no experience in electronics or vacuum tube circuitry, please read through these posts. Do not be discouraged, but do be safe. There are voltages present in this set when the underside of the chassis is exposed that can kill you.
The Schematic is available at Nostalgia Air, a wonderful service that provides "Rider's" Schematics at no charge. Google it. The Website is fairly intuitive. Hopefully, this link will work:
http://www.nostalgiaair.org/PagesByModel/521/M0013521.pdf
Look at your old speaker. The 2 solder lugs directly on the frame of the speaker are the "voice coil" connections. The new speaker will have the same thing. Connect the wires from the "secondary" of the Audio Output Transformer" to these solder lugs. Polarity is not important because this is not stereo. There are 2 wires from the frame that go to a "winding" on the Field coil (generates the magnetic field, your new speaker will not have this). Ignore these. These are connections to the "hum bucking coil". As to the 2 long wires on your old speaker, these are for the Field Coil, and don't exist on your new speaker, but must be dealt with. The simplest thing to do, if there is room in the radio (and I bet that there is not) would be to mount the old speaker, or at least the field assembly (after you cut it away from the frame of the old speaker) somewhere inside the radio. For example, if the cabinet is big, mount the entire speaker frame either behind the replacement speaker or ion the underside of the radio. If there is no room for the frame, mount the field coil somewhere on the chassis, near the power supply area and away from the tuner. Consideration must be given to electrical and heat safety issues. If there is no room for the field coil, it can be replaced with a 1600 (1.6K) Ohm 5 watt (or better yet, 10 Watt) resistor. Again, consideration must be given to locating this resistor as to electrical safety and heat. If you can obtain an aluminum encased chassis mount version of this resistor, this will be good. If you replace the field coil with a resistor, change the two power supply electrolytic caps, labeled 57 and 49A to a higher value start with 20uF for both caps. If there is too much hum, increase to 33 uF for cap 40A. Do not exceed 33 uF for the cap labeled 57 between the 7Y4 cathode and center tap of transformer secondary. the cap labeled 40 (likely in the same "can" as 40 A should remain at 4uF or 5uL. Don't go much higher or this will put too much load on R42.
Keep asking questions if you need help. Good Luck!
Best Regards,
John, MrFixr55
RE: 4x6 Speaker Question for 42-345 - Ron Ramirez - 02-09-2022
A better quality schematic is available on this very site.
https://philcoradio.com/library/download/service%20info/yearbooks/1942/split/Part22-Philco%201942%20RMS%20Year%20Book.pdf
You can get schematics for all 1928-1953 Philco radios without leaving this site. Just look in the Philco Library.
RE: 4x6 Speaker Question for 42-345 - cdoyal - 02-09-2022
"The 2 solder lugs directly on the frame of the speaker are the "voice coil" connections."
The existing speaker only used one lug of the voice coil. Interesting.
"Mount the field coil somewhere on the chassis, near the power supply area and away from the tuner."
This is probably the best option since there is so little room in the cabinet. I've already recapped the whole thing including electrolytics.
RE: 4x6 Speaker Question for 42-345 - MrFixr55 - 02-09-2022
Hi Cdoyl,
Look at the old speaker carefully. There are 2 "coils" in that field coil. The one with a high resistance of 1600 -1700 is the one connected between the + terminal of the 2 Caps, 57 and 40A. The other coil is the "hum bucking" coil which you can either leave out of the circuit or put it in. However, if you use it, polarity is important. one direction will "buck" the hum; reverse the connections, and the hum will be boosted. Use the best of the 3 options. The Voice Coil does have 2 connections. one may be directly to the frame of the speaker. Car radio manufacturers did this a lot in the 50s, and Philco was a major car radio manufacturer.
The Schematic that Ron Ramirez shares in his link shows the connection between the hum bucking coil and the transformer to be grounded to the chassis.
If you can post another pic of the speaker with the voice coil and hum bucking coil connections more visible, this will be helpful, as well as a pic of the wiring extending from the Output Transformer secondary.
Best Regards,
John, MrFixr55
RE: 4x6 Speaker Question for 42-345 - cdoyal - 02-12-2022
Here's another angle.
RE: 4x6 Speaker Question for 42-345 - Ron Ramirez - 02-13-2022
One end of the speaker voice coil is connected to ground (the metal frame of the speaker) through the hum bucking coil.
I believe I would try and find a speaker from another Philco. Models 42-340 and 42-345 use the same speaker. A 42-340 parts set shouldn't be too difficult to find. You would want one with a 1700 ohm field coil.
RE: 4x6 Speaker Question for 42-345 - MrFixr55 - 02-13-2022
Hi Cdoyl, Yes, that pic clears it all up, and Ron confirms it The reason that you have only 1 wire for the voice coil is because the other lead of the voice coil connects to the "hum bucking coil" of the Field. the other end of the hum bucking coil conects to the speaker frame which is screwed solidly to the radio chassis at 4 different points. One lead of the output transformer secondary is likely connected to chassis ground in a similar manner.
Getting another speaker from a Parts Set is the cleanest way to go, but by using the existing speaker for its field, connecting the one existing voice coil lead to the voice coil and connecting the other voice coil lead to chassis ground using an existing screw and a ring terminal will allow you to enjoy the radio now until an exact replacement is found.
Another way to go is to mount the original speaker in its place. Note that there is terminal for an external speaker on the chassis rear. It is only one screw, marked "3" The other 2 screws are for the antenna. A chassis screw is the other connection. Philco did this on several models, including the 41-255, 42PT94 and 47-203 in my collection. Not sure why they did this because this will mismatch impedance, but i also allows a bigger speaker.
RE: 4x6 Speaker Question for 42-345 - cdoyal - 02-20-2022
I'm curious. Why can't the field coil be removed from the circuit entirely and a modern speaker installed?
RE: 4x6 Speaker Question for 42-345 - mikethedruid - 02-20-2022
The field coil acts as a filter choke in the power supply circuit. One CAN substitute a resistor of suitable wattage and the same DC resistance as the field coil, however the power supply will not be as well filtered and one will get hum. Of course, if you change the speaker, you will need to remove the output transformer from the old speaker to use with the new one, or use a new output transformer with suitable impedance matching characteristics. If the field coil on your old speaker is OK, and the voice coil is OK, even if the speaker cone is badly damaged, it is better to re-cone the speaker than to substitute a new one. Unless the cone is badly damaged, they can often be patched using black RTV glue and pieces of paper towel.
RE: 4x6 Speaker Question for 42-345 - Radioroslyn - 02-20-2022
Pretty sure why Philco uses one of the screw terminals as a speaker connection is not really for a spkr connection but as a test point. To measure the ac voltage across the vc to peak the IF an rf coils.
RE: 4x6 Speaker Question for 42-345 - MrFixr55 - 02-20-2022
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.