The PHILCO Phorum

Hi all,
I have an old Philco 42-322 that powers up and works great. However, I want to try to restore and modernize it by adding a Bluetooth board using the method from this website so that the audio will still play through the original speaker (which is in great working order). Admittedly I’m not as knowledgeable about this stuff, but I used this same method to add Bluetooth to an antique Westinghouse radio a while back and it works great. However, now that I’m trying to do the same to the 42-322, I’m struggling to figure out the correct wires I’ll need to disconnect to run new wires to the Bluetooth board, and I want to make sure I’m looking in the right place before taking anything apart. Would anyone be able to offer guidance on the correct location for the speaker solder terminals, as well as the correct wires to remove and replace on the potentiometer soldering terminals? I’ve tried looking at the schematics and just haven’t been able to figure it out, so any help would be greatly appreciated!
Thanks,
Nate

Welcome to the Phorum!


The 42-322 has an electrodynamic speaker that requires the radio to be operational and the field coil that provides the magnetic field for the speaker to be working. I noted in the article you mentioned the following advisory for using the method #2: "Important Note: Commenter J.W. Koebel brought to our attention that if you want to use the radio’s original speaker like we do in this project , the speaker needs to be a permanent magnet speaker."

So, you would need to put in a permanent magnet speaker to follow that course.

Thank you Bob! Glad I asked before taking anything apart .

For my own understanding, how do you know if a speaker is electrodynamic versus a permanent magnet speaker? Just by looking at the model specs? Or is there a way to be able to tell by looking at it?

Thanks,
Nate

Component #42 in the schematic is the field coil.  While its not located near the speaker in the schematic it is part of the speaker assembly.  Schematics show electrical connections, not physical locations. In this case, the info from Philco on this model also has some discussion of the radio near the beginning that mentions the electrodynamic speaker.

Welcome to the Phorum, Nate! The difference between an electrodynamic speaker and a permanent magnet speaker is easy. As the name indicates, a permanent magnet speaker uses a magnet core to drive the voice coil. With an electrodynamic speaker, an iron core is used, then wrapped with a field coil. When the radio is turned on, the coil magnetizes the iron core. Others here can give you more exacting information regarding the two types of speakers. The quality of magnets in that era was sketchy at best and not known for holding their magnetism. The electrodynamic speaker solved that issue with the electromagnet core. As magnets progressed PM speakers were used and electrodynamic speakers were phased out as the PM speaker was less expensive and simpler to produce. Hope this helped.
Take care and BE HEALTHY! Gary

  There is a more to that speaker than just the field coil. It has the output transformer attached and built into the magnetic path for the voice coil is not only the field coil there is also a hum bucking coil. Direct substitution with a PM speaker and still have the radio power the amplifier section would require moving and remounting output transformer and adding additional filter condenser value to compensate for the hum reduction action of the hum bucking coil. That is if operation is desired. Alternatively simply replacing the speaker, leaving the radio OFF or disconnected and mount power and a switch for Blue-tooth.

Another method is to fully restore the radio. Get a blue-tooth to AM band transmitter and tune in the blue tooth station.

A third method is to locate and install an audio input that turns off the AM audio and enable a Blue tooth audio input to the amp. There will have to be some sort of impedance matching for the audio signal.

Since I am both a collector and restorer of my radios, my preference is the Blue-Tooth AM broadcaster. I have as yet to find one for myself though Advantage is any radio will work with it and no radio is modified...

Chas

As I said, others will tell you the 'particulars' in as much detail as you need regarding the two speakers. I just touched on visual aspects. You said the radio plays great ... has it been serviced recently or playing on old internal components? If the latter, I would not play it again until all capacitors and any out of service-range resistors be replaced. Operating with old parts can end up in catastrophic situations when they fail. Take care and BE HEALTHY! Gary

Hi Nate, 

First off, welcome to the Phorum and a Blessed Thanksgiving to you.



Secondly, I read the attached article and not to disparage the author, I think that there are several issues:

1. The "Mods" suggested (Disconnecting the radio's audio output from the speaker and disconnecting all connections from the volume control) will render the radio to be inoperative, destroying history.
   
2. Safety!  both your Philco and the radio in your attached article is of the transformerless AC-DC variety, as are most of the tabletop radios made between the mid to late 1930s and the end of vacuum tube radios.  More on that later.  These mods or repair and restoration of the radio should not be attempted unless the person doing so understands electricity and electronics, can read a schematic, has good soldering skills and a healthy respect for line level and high voltage.
   
3. The speaker.  As other folks, including experts have stated, your radio uses an "electrodynamic" Speaker.  All dynamic loudspeakers work by the varying audio signal, connected to the "voice coil", attached to the cone of the speaker, attracting or repelling the steady magnetic field set up set up in the field pole piece of the speaker.  In a "PM" (Permanent Magnet) dynamic speaker, the field pole is a strong permanent magnet.   In the "electrodynamic speaker, the field pole is an electromagnet, powered by DC power from the radio's power supply. 
   The radio in the article had an electrodynamic speaker.  If the author used that speaker in the video demo, then he was using the radio's power supply to power the speaker.  This presents a safety issue, explained below:  

Most tabletop radios built from the late 1930s to the late 1960s and the end of the vacuum tube era were of the "AA5" (All American 5) design, so called because almost all radios produced in the USA in this era used this AC-DC Circuit with very few variations.  Although your radio is a 6 tube, it is of this design.  The big safety issue here, is that there is no power transformer.  Power transformers isolate the chassis from the AC Power line.  In the AA5 radio, the chassis is connected to the power line, either through a capacitor and resistor or in some cases, directly connected.  The power in your house has one leg, called the "neutral" leg grounded.  The other leg, the "hot" leg is at 120V (Volts) above ground potential.  Now, if the chassis is connected to the neutral leg, there is no issue.  If the chassis is connected to the hot leg, then the danger of shock is real.  Since the power cord is not polarized (to allow only one way to connect, so the chassis is at neutral potential), you have a 50% chance of having the chassis being hot.  To make matters worse, on this radio and almost all radios of the AA5 AC-DC transformerless variety, the power switch is in the "neutral" (chassis) side instead of the hot side.  So if the power plug is connected in the polarity that puts the chassis on the neutral leg with the switch on, the chassis becomes hot through the tube filaments when the switch is off.  a cold tube filament has a very low resistance.
 
Most restorers and experts on this Phorum recommend the following:

• Installing a power cord with a "polarized" Plug.  The thick blade is the neutral leg and the thin blade is the "hot" leg.  The neutral is connected to the "ground side" of the circuit (negative of the power supply, 1st AF tube filament leg of the heater "string"). 
  
• Rewiring the power switch so it is on the "hot" side (rectifier plate and resistor or rectifier filament of the heater string).
  
• Replacing the "electrolytic" power supply filter capacitor. 
  
• Replacing all "paper" capacitors.
  

Again, knowledge of electricity and electronics, the ability to read a schematic, good soldering skills and a healthy respect for electricity are absolute requirements for performing this work.

If you have good electronics skills and can read a schematic, you can modify the radio by adding an audio input.  this is not horribly difficult.  You need:

• An "RCA" jack
  
• A SPDT (Single Pole Double Throw) switch.
  
• The schematic.
  

Perform the following:

• Restore the radio as above, adding the polarized cord, moving the power switch to the hot side and replacing all elecgtrolytic and paper capacitors.
  
• Disconnect the connection at the junction of the volume control and Detector circuit (a black wire that goes to the 2nd IF transformer and Cap 27e and resistor 27D on the schematic)  
  
• Connect the common terminal of the SPDT switch to the volume control.
  
• Connect the black wire removed from the volume control to one leg of the SPDT switch
  
• Connect the other leg of the SPDT switch to the center pin of the RCA jack.
  
• Connect the shell of the RCA jack to the chassis.
  

I attached a section of the schematic showing where to add the switch and jack (the red arrow is the connection to break).  This will give the best performance and a Bluetooth receiver can be connected to this point to prevent the need to have a wire running from the iPod or whatever and the radio. 

If you are not comfortable doing this, then an alternative is a "home AM transmitter".  These are low output, are legal under FCC Part 15 rules and some are easily tunable to a "dead" spot on the AM band.  The easiest to use is the iAM "Talking House" transmitter.  This is not cheap, they run about $170 on Amazon, eBay and other websites.  There are nicer ones such as the SSTran but these are much more expensive.  There are cheaper kits available, but the skills above are needed.  

I hope this all helps.  Keep asking questions, we are all happy to help!

Best Regards, 

John "MrFixr55"