[Arran]

I think you could solve the current issue with filter chokes by using two in parallel, but I'm pretty sure that you would need two identical ones that are each double the DC resistance you need, that is unless the 675 ohms is measuring reactance and not DC resistance Or you could just pick the one that's closest in current rating, but is at least in the ballpark for DC resistance. It's the inductance in Henries that is important, but it's very seldom that the service data would tell you what that is. You could also try making a solid state filter choke, as documented in a back issue of the AWA Old Timer's Bulletin. I just hope that the 8000 ohm section of the field coil wasn't used for filtering the B- leg of the power supply, or something like that, where you can omit it without consequence.
Given the technical specs on these speaker I can't figure out why the audiophools in Asia or elsewhere would want to play with them, they seem like a PITA to use outside of a McMurdo.
Regards
Arran

[Ron Ramirez]

No, Arran, the 8000 ohm section was connected between B+ and ground, so it only served to "excite" the speaker. The 680 ohm section is the one that was used as part of the set's power supply.

Arran, can you send me a copy of that article about the solid state filter choke? Sounds interesting...

Edit/added info: All resistances given are DC resistance, not AC reactance.

If you come up with a way to supply DC to the fields, then you can use an electrodynamic speaker in pretty much any application...which is apparently what the audiophools are doing. But it seems to me that it would be much easier to just use modern PM speakers to get the sound they want. Who knows, perhaps they think these Jensen Super-Giants possess some sort of magical powers or something.

[Conelrad]

Allegiance to the Jensen field-coil pedestal speakers comes from the use of them by the Electrical Research Products division of Western Electric in their movie sound reproduction systems of the 1930's. Some were even rebranded, making them even more 'holy'.

Obviously they weren't bad speakers, and in the day were just about the only thing that could handle the power @ frequency needed in a large movie house.

A radio in your home with one or more would have been ne plus ultra in terms of audio reproduction.

Dennis

[Ron Ramirez]

Yup, Dennis, you hit on the magic words - Western Electric.

The new woofer and tweeter arrived today. Sometime this week, I'll start cutting the steel pieces I bought yesterday and assemble my own coaxial speaker!

[Eliot Ness]

Ron, Leigh Bassett is the person who came up with the SS filter choke:

http://www.antiquewireless.org/otb/resto0504.htm

[Arran]

Here is a 15 inch Magnavox pedestal speaker, speak of the devil, I think the price is too high but at least it isn't four figures.

http://www.ebay.com/itm/Vintage-Magnavox...3a7e75f1c0

They were good enough speakers for Canadian Marconi and Canadian Westinghouse, along with some Rogers built sets.
Regards
Arran

[Ron Ramirez]

Eliot (John) - Thanks very much for the link! Very good info. Unfortunately, this circuit is designed for 100 mA max B+ current. With 21 tubes, I suspect the MP VI will be running more like 150-200 mA. I'll email Leigh and ask his opinion. He is doing a great work with his Atwater Kent info and schematics website.

http://www.atwaterkent.info/

Arran - That is a neat Magnavox speaker! Too bad it's a 15 and not an 18, though. Yes, it's expensive, but if that were a 1930s Jensen instead of a 1930s Magnavox, it would have been gone within minutes of its posting at that price.

[Ron Ramirez]

I've cut the steel into four pieces of equal length, and have drilled a hole in one end of each. I assembled the steel arms to the tweeter and did a test fit on the woofer.

Whew! I cut them long enough! You know what they say about measure twice, cut once...

I then removed the arms from the tweeter and put both tweeter and woofer back into their protective cardboard.

Tomorrow, I'll drill holes in the other end of each arm for mounting onto the woofer. I'll also have to pick up four more screws - the ones I have are too short for mounting the arms to the woofer, but perfect for mounting the arms to the tweeter.

Will post some pictures soon. If nothing else, this coaxial speaker will look good...

[Arran]

I think the 15'' Maggy I have from a Northern Electric console is very similar to that red pedestal unit other then it does not have the pedestal, I doubt if they will get near $300 for it but who knows? It definitely has to be a cult thing with the Jensen 18'' speakers, and the dubious Western Electric connection makes about as much sense as anything with the audiophools. I've noticed that the more normal sized Jensens don't get anywhere near that amount of money, though some try asking it.
It's sort of like General Motors built V16 Cadillacs, which are a high end classic car often with custom built bodies, but they also made more ordinary Cadillacs with V8s and millions of cheap Chebbies sedans too, same goes with Jensen and their speakers. The logic here also seems to be that Hollywood star X (Western Electric) owned a V16 Cadillac therefore Packards, Lincolns, Duesenburgs, Imperials, and Pierce Arrows aren't any good.
Regards
Arran

[Ron Ramirez]

Progress report...

I started off with a 3 foot section of steel:

[Image: http://www.philcoradio.com/images/phorum...94b082.jpg]

and then cut four equal sized pieces, each 7-15/32" in length:

[Image: http://www.philcoradio.com/images/phorum...a76f39.jpg]

Here's the new 4 inch tweeter, with a frequency response of 3000-20000 Hz.

[Image: http://www.philcoradio.com/images/phorum...f5439b.jpg]

There are scratches on the mounting flange from my previous "test fit" of the steel pieces.

Add the steel to the tweeter, and we have this:

[Image: http://www.philcoradio.com/images/phorum...5d070e.jpg]

More to follow...

[Ron Ramirez]

Now let's bring in the woofer. It has a frequency response of 20 to 6000 Hz.

[Image: http://www.philcoradio.com/images/phorum...430c5e.jpg]

[Image: http://www.philcoradio.com/images/phorum...79a0de.jpg]

This thing is as big as several of my radios and even bigger than others!

With a woofer response of 20 - 6000 Hz and a tweeter response of 3000-20000 Hz, using a crossover network with a crossover point of 4500 Hz, this speaker will produce the full audible range of 20 to 20,000 Hz. Certainly the radio will not be producing that kind of frequency response on AM or SW, although the McMurdo's audio amp is probably capable of producing that entire frequency range. Once the set is done, playing something through the McMurdo's microphone input should prove interesting.

Anyway, the next step is to mount the tweeter coaxially in the middle of the woofer. I found that by simply laying the arms on the woofer gasket and tightening the screws/nuts, that the steel sank down into the gasket, making the steel rub against the outer accordion edge of the woofer's cone - not good.

Then I remembered these:

[Image: http://www.philcoradio.com/images/phorum...1a7e5a.jpg]

Nylon washers that I had bought at a hardware store, that turned out to be too big for use in lamp sockets. But now I can use them as spacers:

[Image: http://www.philcoradio.com/images/phorum...476a19.jpg]

These will keep the steel arms from sinking into the woofer's gasket and will keep the arms suspended above the woofer's accordion edge!

Finally, here's how the homemade coaxial speaker looks all together:

[Image: http://www.philcoradio.com/images/phorum...a2d482.jpg]

[Image: http://www.philcoradio.com/images/phorum...324b3f.jpg]

[Image: http://www.philcoradio.com/images/phorum...f99211.jpg]

The next step is to attach wires to both speakers, then attach the speaker inside the McMurdo's Clifton cabinet. I bought some stick-on gasket material to help ensure a tight seal between speaker and sounding board, and I'll be using some of this when I put the speaker in the cabinet.

[jontz]

Looking good Ron! I don't know anything about the cabinet you are mounting this in, but I am curious as to whether or not the tweeter sticking up above the edge of the woofer will interfere with mounting or not.

[Ron Ramirez]

I'll have to look into that for certain. I could flex it downward, too, but this might increase the chance of the woofer cone's accordion edge hitting the steel on loud passages.

Here's what it will be going into:

[Image: http://www.philcoradio.com/images/phorum..._00002.jpg]

Back view of the Clifton cabinet:

[Image: http://www.philcoradio.com/images/phorum..._00003.jpg]

Yes, that is a Scott Philharmonic speaker sitting in there, too small for the opening. It came with the McMurdo when I bought it. The Scott speaker will be going into my Scott Allwave 23 as it has a Philharmonic amp/power supply.

I didn't want to cut a hole in the sounding board to mount a tweeter separately, since this is such a rare and desirable set. It's bad enough that I'm using modern speakers, but like I said at the beginning of this thread, I'm just not going to pay $6700-9000 + for the original. I can't afford it, for one, and besides, that sort of price for a speaker is ridiculous - in my opinion.

[GarySP]

Hey Ron...nice adaptation of modern speakers for a magnificent radio. Why don't these fall into my lap? BTW ...You might want to add a drop of threadlock on the nuts and bolts you're building the coaxial speaker with on the steel spans. I'd hate to have to pull the speaker back out a few months down the road because the vibration worked the bolts loose and are humming now. Regards to all. Gary

[codefox1]

I would have used lockwashers as well as threadlock, but your experience may vary.