Speaker/OPT question

[natedogg643]

I have an old Zenith floor stander (5r337) that I'm trying to bring back to life. The speaker cone is shot. It has a transformer bolted onto it. Am I assuming correctly that this is the output transformer? It's a basic looking 5" speaker, and the schematic I have references part number 49-238-5". Can I replace it with any 5" full range speaker? Or should I try to refabricate the cone? Or should I look for an old speaker somewhere? Thanks,

Nate

[Tubes&Mosfets]

Originally Posted by natedogg643

I have an old Zenith floor stander (5r337) that I'm trying to bring back to life. The speaker cone is shot. It has a transformer bolted onto it. Am I assuming correctly that this is the output transformer? It's a basic looking 5" speaker, and the schematic I have references part number 49-238-5". Can I replace it with any 5" full range speaker? Or should I try to refabricate the cone? Or should I look for an old speaker somewhere? Thanks,

Nate

You are right in your assumption.

Many options available. You can have the speaker reconed (or DIY) for about 35$ (you decide if the radio is worth that much to you). You can also replace the speaker with a run-of-the-mill 4 ohms speaker (yes, 4 ohms). keep the original output transformer if you are replacing the speaker.

Do not use a foam surround speaker, try to buy a car speaker with a paper surround. The impedance and "stiffness" will be right. I find them locally in electronics surplus store for a few bucks. If you are replacing the speaker, keep the original in a safe palce just in case you wish to have it reconed to keep originality or wish to sell the radio.

Z-

[David Roper]

If you opt to simply replace the speaker, you'll end up wondering what to do with all those extra wires. Your radio's speaker (like virtually all of that era) has an electro-magnet inside the bell which is called a field coil. The field coil serves the dual purpose of speaker magnet and power supply choke. Ideally it should be replaced by an outboard choke of similar characteristics--that is, inductance and maximum current ratings should be close to that of the field coil. A new choke which is close in such respects will probably be quite a bit lower in resistance, so you can add resistors in series with the choke to match the original resistance.

Or just forget a choke and replace the field with a (very large) power resistor, but if you do that you'll probably have to increase the values of C12 and C13 to avoid increased hum. I'd pop for a choke if it were me.

[Tubes&Mosfets]

Originally Posted by David Roper

If you opt to simply replace the speaker, you'll end up wondering what to do with all those extra wires. Your radio's speaker (like virtually all of that era) has an electro-magnet inside the bell which is called a field coil.

Good point.

Here's the schematic: http://www.nostalgiaair.org/PagesByM...7/M0024987.pdf

I know the field coil can be replaced with a small 6V transformer and tuned with one or two caps of around .01uf in value if a _proper_ choke isn't available. Or if the OP is somewhat adventurous and knows about solid state circuits, a transistor or MosFet can also be used wired as a capacitance multiplier.

Z-