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Philco 38-5 Speaker - Printable Version

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Philco 38-5 Speaker - Geoff - 03-13-2012

Ron,

You had replied back to me in the Wanted Ads thread about my missing 38-5 speaker:

RE: ATTN Ron Ramirez: WTB Philco 38-5 Speaker
Okay...I had forgotten to whom I had sold that radio!

I've since replaced it with another 38-5B, and wouldn't you know it, this one has a speaker, but it is not an original Philco speaker.

Anyway...

The original speaker used was a K-39. 660 ohm field, 1.25 ohm voice coil. Primary impedance of the push-pull output transformer: 14,000 ohms.

Now you need to replace it.

You need a speaker with a field coil in the range of 660 ohms (650 is OK). You can always mount a new "universal" push-pull output transformer onto a replacement speaker.

There are a few other Philco models that used speakers with 660 ohm fields, but not very many. Here's the list:

K-23: Used in Model 19 Code 128, and Model 144B. (Uses a single ended audio output transformer that will have to be replaced with a push-pull unit.)
K-34: Model 37-640B. (Original push-pull transformer will work in the 38-5.)

Your other option is to install a PM speaker and replace the field coil with a 660 ohm, 25 to 50 watt resistor. 25 is actually large enough but 50 gives you a greater margin of safety.

I think I would have a hard time finding the K-23 or K-34 speakers. I looked on eBay and found a couple but they are in full sets. I think my best option would be to purchase a modern permanent magnet speaker. However, I'm not sure how I would actually hook it up. According to the schematic it looks like there would be 3 wires going to the K-39 speaker but there are 4 wires that connect to the speaker plug. A modern PM speaker has 2 connection lugs. How would I actually connect the wires from the plug to the PM speaker? Where would I connect the 660 ohm resistor?

Thanks,
Geoff

RE: Philco 38-5 Speaker - Arran - 03-14-2012

(03-13-2012, 11:43 PM)Geoff Wrote:  Ron,

You had replied back to me in the Wanted Ads thread about my missing 38-5 speaker:

RE: ATTN Ron Ramirez: WTB Philco 38-5 Speaker
Okay...I had forgotten to whom I had sold that radio!

I've since replaced it with another 38-5B, and wouldn't you know it, this one has a speaker, but it is not an original Philco speaker.

Anyway...

The original speaker used was a K-39. 660 ohm field, 1.25 ohm voice coil. Primary impedance of the push-pull output transformer: 14,000 ohms.

Now you need to replace it.

You need a speaker with a field coil in the range of 660 ohms (650 is OK). You can always mount a new "universal" push-pull output transformer onto a replacement speaker.

There are a few other Philco models that used speakers with 660 ohm fields, but not very many. Here's the list:

K-23: Used in Model 19 Code 128, and Model 144B. (Uses a single ended audio output transformer that will have to be replaced with a push-pull unit.)
K-34: Model 37-640B. (Original push-pull transformer will work in the 38-5.)

Your other option is to install a PM speaker and replace the field coil with a 660 ohm, 25 to 50 watt resistor. 25 is actually large enough but 50 gives you a greater margin of safety.

I think I would have a hard time finding the K-23 or K-34 speakers. I looked on eBay and found a couple but they are in full sets. I think my best option would be to purchase a modern permanent magnet speaker. However, I'm not sure how I would actually hook it up. According to the schematic it looks like there would be 3 wires going to the K-39 speaker but there are 4 wires that connect to the speaker plug. A modern PM speaker has 2 connection lugs. How would I actually connect the wires from the plug to the PM speaker? Where would I connect the 660 ohm resistor?

Thanks,
Geoff

I would use a filter choke rather then a resistor, unless it's just temporary, there is even a solid state circuit that may work as a choke substitute, a used one will do, so will a 9 inch electrodynamic of another brand, even though the bolt pattern is a little different. But don't give up looking for a speaker though, you best bet to find one is to hit the swap meets and look for junkers.
Regards
Arran


RE: Philco 38-5 Speaker - Geoff - 03-14-2012

OK, but I'm still a little hazy about where to make the connections.

RE: Philco 38-5 Speaker - Ron Ramirez - 03-15-2012

OK, I finally found a little time to scan the 38-5 schematic.

Click the thumbnail to see a larger version:

[Image: http://i326.photobucket.com/albums/k420/mrphilco/Phorum%20Stuff/th_38-5_schema.jpg]

There are four wires going to the original electrodynamic speaker in the 38-5. These are used to connect the primary of the audio output transformer, and the speaker field coil.

One of those four wires serves a dual purpose - it is connected to the center tap of the audio output transformer plus to one lead of the speaker field. This is why there are four wires, and not five.

The partial schematic below is intended to make things clearer:

[Image: http://i326.photobucket.com/albums/k420/mrphilco/Phorum%20Stuff/38-5_part.jpg]

In this partial schematic, I have labeled the leads going to the speaker in larger type.

The GREEN and WHITE leads run from the plates of each 6F6G output tube to the primary of the audio output transformer.

The GREEN-WHITE TR. (green with white tracer) lead is connected to both the center tap of the audio output transformer, and to one end of the speaker field coil.

The BLUE-WHITE TR. (blue with white tracer) lead connects to the other end of the speaker field coil.

If you use a PM speaker to replace the original, you will need to connect your resistor inside the chassis to the same points where the BLUE-WHITE TR. and GREEN-WHITE TR. leads connect inside the radio.

The replacement speaker should have the audio output transformer mounted on it, as the original did. Now you will only need three wires running to the speaker, and connected to the primary of the audio output transformer. Those wires are GREEN, WHITE, and GREEN-WHITE TR.

I hope this clears things up.

RE: Philco 38-5 Speaker - Geoff - 03-22-2012

Thanks Ron. I appreciate your response. I don't want to say that I 100% understand your response but I'm going to read it a few more times and hopefully it will sink in.

Thanks!!!

Geoff