[SteveJB]

This is an early one from '33.  It has no speaker. I have to find one or use a pm.  

Does anyone know which one it used?  Is it the same as any other sets that era?  I do have two on hand from 16x consoles. Would one of them work?

P S. I haven't picked it up yet. Will know more later in the week.

Steve

[fields 100]

I can't be sure as I do not have console, but it is not likely. I just measured mine and it is only 7.5" in the outer diameter and 8.25" between the mounting holes across. Yours probably 10.5", which they used on the 16B tombstone.

[Steve Davis]

Steve, if this is the cathedral style 16B, you will need a K-17 speaker. 

Steve

[SteveJB]

Thank you.  Do you know how I would find out what other radios used the same one? It would help with the parts search and I am not sure where to look.

[Steve Davis]

Other models that used the K-17 speaker were 14B, 17B,18B and 118B. You could also use a K-7, K-21, or a K-22 and probably a few others but you would have to replace the output transformer with one designed for push-pull output and disconnect the bucking coil.

Steve

[Mondial]

Steve, if you used another speaker why would you want to disconnect the hum bucking coil? I can't think of any downside of having the bucking coil, even if the original didn't have one.

[Steve Davis]

I would probably try it both ways. I'm not an expert on this but the way I understand it, with push-pull output, if there is any ripple on the B+ it is canceled out in the primary of the output transformer. With a single ended output, they add the bucker coil to produce a signal 180 degrees out of phase to cancel the hum. Now, what I'm thinking is, with a push-pull output, with a bucker coil, the hum would be canceled in the primary of the output transformer, then you would add this 180 degree out of phase signal that would create the hum again. 

Steve

[Mondial]

That's an interesting explanation and it makes sense, but I have seen original speakers with push pull output transformers also equipped with bucking coils. 

The way I always understood it, the bucking coil was used to cancel the hum caused by using the field coil as the first filter choke. In this case, the large ripple current component modulates the magnetic field and causes a hum voltage to be induced in the voice coil.  By connecting the bucking coil in series and out of phase with the voice coil, the induced voltages cancel and the hum is reduced or eliminated. 

In a lot of radios I have worked on, if there is a separate filter choke after the rectifier and then the field coil as a second choke, the bucking coil is not used. In this instance, there is little ripple current in the field coil so the bucking coil is not necessary.

In any case, it would be a good idea to try it both ways, with and without the coil to see which resulted in a lower hum level