I don't know if I'm on the right track or not. I have a Zenith 6S229. It came without a speaker. So I found a Zenith speaker, that was with a Zenith 6S321 chassis on ebay. I bought this to use the speaker on my 6S229. Plugged it in and no sound at all. How do I check to see if coil could be bad on speaker?

Or, what else could be wrong? I'm open to just about anything.

P.S. I can't get any kind of noise out of the speaker whatsoever. Not even any kind of static.

Thanks,
Greg

You can test the speaker with an ohmmeter. The speaker assembly should have a field coil, an output transformer, and a voice coil.

The field coil should measure about 1200-1300 ohms. The output transformer is mounted on the speaker. The primary winding of the output transformer should measure around about 800-1200 ohms, although the actual measurement is not too critical.

To measure the voice coil and the O.T secondary, one wire has to be disconnected since the two windings are connected to each other. The secondary off the O.T. should measure just 2-3 ohms. The voice coil will measure about the same. Remember to reconnect the two when you are done testing.

Don't be too quick to blame the speaker. If the radio came to you without a speaker, are you sure that the radio was working before?

Thanks for the reply, Paul. No I'm not sure it's the speaker, but I wanted to try something quick 1st. I did do something that someone on the web said I shouldn't do. I measured the voltage output on the 5Y4 with the speaker unplugged. It is what the specs call out, 330 ish. It is low when the speaker is plugged in, well below 200v. Any thoughts on that?

Greg

Low B+ voltage tends to indicate something loading down the 5Y4 tube. It could be a leaky or shorted capacitor like C17.

Has the radio ever had the electrolytic filter capacitors replaced, (C16 and C17)? This is highly recommended when testing an old tube radio with the power on.

Failing to replace these capacitors could result in damage to the set that could be expensive to repair. The capacitors on the other hand are pretty cheap (insurance).

http://www.nostalgiaair.org/PagesByMode ... 025209.pdf

Yeah, Paul. I replaced all caps, except for mica caps, before I even turned it on. Your speaking of loading down the 5Y4. That's what happens when the speaker is plugged in. It drags that voltage way down from 330v to below 200v.

Greg, here are a couple things to check:

Double check that the negative side of C17 is wired correctly to the R12 Candohm resistor. A reversed electrolytic will load down the B+

If it is wired correctly, measure your B+ voltage again with the 6F6 tube unplugged, and note if the voltage is closer to normal, around 250 VDC.

Leave the power on no longer than necessary to make your live voltage checks.

Also, does the replacement speaker plug use three pins?

No. It uses 4 pins

No it uses 4 pins, and measured B+ wth tube out. Still reads less than 200v. Caps in correctly

Greg, Since the speaker is not original to your radio, there is a chance that the plug and cable are wired differently for the 6S229 speaker. My Zenith schematics don't show the speaker plug and wiring for either model.

Based on the schematic, try to identify each pin, and where it is supposed to go on the radio speaker socket.

Then trace out where they go on the replacement speaker. I think you need to rule out the possibility that a crossed connection on the speaker assembly could be loading down the B+ voltage.

Before I even dreamed of subbing in another speaker, I'd verify the resistances of the original speaker. If you find something shorted, or open, then you can try the sub IF it too is on good shape.

Hold the speaker plug with the prongs facing you. The two top ones closest together is the field coil. The furthest outer prongs is the primary of the output transformer.
Use the Ohmmenter to do the checks.
The field should be about 1250 OHms. The primary (on my set ) measured about 260 Ohms.

Measure the pins to the speaker frame. Perhaps the field is shorting on the frame somwhow?

Measuring the "B+" without the field coil installed is a bad idea.
(Someone help me out, I can't find the post. I think it had to do with the B+ going too high without the load on it?)
As you can see you are measuring the filament takeoff of the plate voltage. You are going to have to have a load there as your final B+ is taken after the second filter cap. Passing through the field coil.


Check the Candohm for proper resistance.(Power OFF) Those things are notorious for opens and intermitent operation.

Last test, most basic. Remove the rectifier. Test the transformer voltages. Measure from the negative side of the first cap, C16 and to each of the plate terminals. Pins 3 and 5 seperately.
Don't forget to set the meter for AC.
The voltage on each side of the center tap (neg of C15) to each pin should be pretty much equal.

IIRC, there is one set of pins jumpered together under the chassis. The one side of the field coil and one leg of the output trans.

Even though the speaker plug has 4 seperate pins (easier to check) two of the leads are tied together. See diagram.

OK Gary,

1. Pins were wrong. I thought Zenith would be consistent and make connections the same. But I was wrong. You were right. I made top 2 the field coil.

2. Checked candohm. OK

3. Measured pins to frame of speaker. No short.

4. The difference in primary is: Yours is 260. Mine is 560 ohms. Could this cause rectifier voltage to do what its doing????

5. Coil reads about 1.2K

When I power the radio on, the rectifier voltage stays at 340 ish volts until the tubes warm up. Then voltage drops below 200v.

Greg, if you have cleared any questions about the replacement speaker, and its wiring, you may want to try the following:

You reported that the voltage drops after the tubes warm up. That may warrant some further testing.

With the exception of the 5Y4, remove individual tubes one at a time while monitoring the B+ voltage. Note any increase in B+ voltage when a tube is removed.

This could point to a stage that is loading the B+ down.

OK Gary, if you're ready for this.

With the 5Y4 in, I took out tubes 1 by 1. The 6F5G re-installed B+ OK. The 6H6G re-installed B+ OK. THEN:

With the 5Y4, the 6F5G, and the 6H6G installed the B+ holds up. But as soon as I started installing either the 6A8G, the 6K7G, or the 6F6G 1 at a time with the 1st 3 tubes at the beginning of this sentence, the B+ drops down below 200v. I hope you understood what I just said.

I'M SORRY PAUL, DIDN'T SEE YOUR NAME 'TIL AFTER I RE-READ THE MESSAGE !!!!!

Check the screen voltage on the 6F6. If it is low the tube can conduct a lot of current whithout hurting the tube much, but putting the pri winding of your OP trans in danger.

"Testing for voltage with the FC unplugged allows the 1st filter cap to see the full unloaded voltage of the power trans, less some restance internal to the rect. This coud push it beyound its spec. I have radios with tags warning against doing this - or pulling out all the other tubes. This would put the 2nd filter in danger as well.

I will do this today. My brain did not want to work anymore last night. Also, and going to change filter caps, in case I somehow blew them.

Thanks phlogiston

Voltage on 6F6 pin-5 is -6.2v. Voltage chart says it should be -3.5v ????
Voltage on 6F6 pin-4 is same as B+.

Replaced both filter caps. Still same problem.

Greg

I am running out of things to try. Any other thoughts guys?

Well guys. I found something. In an attempt to start eliminating parts of the circuits surrounding the 6F6, I found that candohm is involved in the problem. When I cut 6F6 pin 8 off of the candohm, between the 27ohm and the 125ohm, the B+ stays high. When I connect it back up, it drags the B+ back down. I disconnected all of the other connections and reconnected them and it seems that it is the candohm by itself that's the culprit. Any thoughts?

Greg

Candohm resistors can be troublesome. In Zenith sets they are used to set the bias for several tubes, so it could be related to causing one or more tubes to conduct too heavily.

Mark each wire on the candohm and disconnect them. With an ohmeter carefully measure each section to see if the resistance is correct. Make sure the readings are stable. The terminals on the candohm are just a pressure connection and can become intermittent with age.

Also, make sure that none of the sections have shorted to ground. The resistance material in a candohm is wrapped in insulating paper and then crimped in the metal sleeve. If the insulating paper becomes damaged, it will short out to ground.

Some guys here just replace them with separate 5 watt power resistors as standard practice because of the problems they can create.