Speaker technologies

[Mark Schroeder]

Looking for technical info all about speaker technologies from the 20’s through the 50’s. Looking for that “rare” detail about dynamic vs non-dynamic, power handling, load, inductance, etc? Can anyone point me references that can give me these? Almost none of the technical schematics of these eras provide this, nor do the various parts catalogs. These just show a “speaker” and of it is a electrodynamic or not. And what the specifications are for these? Did Jensen ever put together a catalog that would help take any mystery out of what the best speakers are for various radio brands? Did Scott ever provide specs for the speakers they sold or recommended for their radios? If so, where would that be found?  Thanks. 

[Norman S Braithwaite]

EH Scott Radio Laboratories never made speakers.  Specifications of Jensen speakers appropriate for the time frame were published by Jensen and in electronic products catalogs which can be found on line.  I have not seen specifications published for Magnavox speakers also employed by EH Scott Radio Laboratories.

Norman

[Mark Schroeder]

Thanks Norman. Do you have a link to any of the technical specs for the Jensen or Magnavox that you can share? Do you know if EH Scott ever recommended a specific model type from Jensen that they had designed the radios and optimized their designs for?

[David C. Poland]

You are on an antique radio site,  mostly pre-WW2 era or shortly after WW2. The standardization to 4, 8 and 16 ohm speakers with permanent magnets is pretty much a post war development.

Prewar radio design engineers included the specs for the speaker too. Voice coil impedances range widely from 3 or 4 ohms to upwards of 38 ohms depending on the design engineer's choice. Often the output transformer is attached to the speaker frame. Pre war magnets were not very good and so, except for battery radios, there was heavy reliance on field coil speakers through the 1930's - the field coil not only energizing the magnet but also acting, frequently, as a choke in the high voltage circuits.  Field coils can range from a couple hundred ohms to 5,000, 10,000 ohms and more and may be tapped to provide more than one voltage reduction. Some E H Scott radio speaker have two field coils. The field coil is shown on a circuit diagram as part of another circuit and is seldom anywhere near the speaker and output transformer on the diagram.  My point being pre-war speakers are often unique to a particular few or only one radio model.

Departing from the original speaker can involve dealing with more than just a speaker choice - because the output tubes must work in conjunction with a proper output transformer for the substitute  speaker. And a proper substitute for the field coil is required as well. 

In contrast,  1920's era speakers are a whole other world. They are higher voltage, low current devices. They preceded moving voice coils technology of about 1929. The modern speaker is a low voltage, higher current device. The purpose to output transformer was to step down working voltage of the tube circuit to match the speaker to the load needed by the output tube(s). 

1920's horn speakers were derived from telephone technology and later 1920's cone speakers were some improvement.  Both operated with a resistance coil of the order of 2000 ohms (more or less) in series  with the plate circuit of the output tube, meaning in a circuit of maybe 20 volts, or  45 or 90 volts or maybe 135 volts or more depending on the radio design and the batteries and tubes used. No output transformer.  Such speakers had poor frequency response by today's standards. Substituting a modern speaker would require adding a proper output transformer too. 

[David C. Poland]

There is a wealth of information on the various E H Scott models on the archive section at the top of this page. For almost every Scott model, the speaker is unique to that model owing to the tubes and circuit requirements. The Jensen and Magnavox speakers were custom  versions of standard theater size speakers - custom as to the voice coil, attached output transformer, the field coil(s) and for the cable plugs. The speakers are not interchangeable  between models (but for one exception that I know of). 

[David C. Poland]

East E H Scott radio was shipped with the correct speaker(s). 

E H Scott Radio is not to be confused with the H H Scott component HI Fi products of the late 1940's, 1950's and 1960's 

[Mark Schroeder]

David, I really appreciate your time and this historical info.

As an owner of a few EH Scott sets, the issue about the speaker specifications has always been something that I could not find enough detail about. You have confirmed one of my concerns about a specific speaker (s) being shipped with Scott radios that was matched to the specific model. But, the gap I have is identifying what that speaker is and the specs for it. Most of the radios I own do not have speakers and as I get closer to bringing them back to life, I really do not want to wait in line and wind up spending a huge amount of money for a matching speaker, when one could easily be built.

My major concern is making sure I can determine the appropriate loading for the output of these. In the case of my "Super 10", the 310 audio output tube is now a major replacement cost (at least in my pocketbook). I would really like to load it minimally, but properly, to be able to try and reproduce the intended audio characteristics that it was designed for. Even though I doubt I will ever find the correct speaker type that was used or preferred, I would like to try and get close. As an example, if I bought a 1929 Radiola 100A speaker and connected it to the Super, its a crap shoot for me if it would work (assuming the speaker is in good condition). That is why I was hoping to find any type of references that may provide specs for speakers of these early 20's and 30's mfgr's and, better still, what the exact speaker model (as opposed to just the mfgr) was used / recommended/shipped in/with most Scott radios during these years.

[Kent King]

Mark -

Well, the 100A speaker will work well with the Super 10 and the type 10 output tube (10/210/310 are all the same). In fact, this is the high impedance speaker type Dave refers to (cone speakers). These speakers are generally not terribly expensive, but sounds quality varies wildly. Also, the Super 10 isn't really considered an "audio" set (ok, NO battery is an audio superstar!). 

Other sets, especially those with field coil speakers from the 30s are the more difficult to match. Do you have other 30s Scott sets where you need a speaker?

Kent 

[David C. Poland]

Aaaah yes!!.  The World's Record Super 10  - meaning the battery set of 1927-8, a kit set ??.  The era of the classic cone speaker, a high impedance magnetic speaker using a horse shoe magnet.

Until Scott brought out the 1929 AC-10 socket power radio,  Scott did not provide the speaker.  Was the buyer/builders choice. One Citizen's Radio Callback magazine article for the Scott  Super 10 suggested the Tower Pirate Ship, a 14 inch magnetic cone speaker (I have one). But I will use the 18 inch Tower Adventurer when I finish restoring my WR-Super10. One could use about any cone speaker, regardless of whether you were using a 10,  or a 71A, in my case. 

Scott did offer an outboard amp/power supply somewhat like the Shield Grid 9  unit on page 118 of the Scott Collectors Guide, 2nd Edition. And I recall another featuring Thordardson transformers that could augment a Scott battery kit. but until nearly 1929, you were still limited to the magnetic cone speaker as the leading edge type speaker technology. I suppose you could rig up an interface to a more modern amp, using your WR-10 output tube as a driver for an outboard amp and modern speaker, is you do not mind the historical inaccuracy.

The 1927 WCFL Radio magazine suggested with the type CX-310 output tube like you have, the big 36 inch Western Electric cone speaker would make the most of the radio audio power, if you can find and afford one now.

[David C. Poland]

For The Scott models of the 1930's, if you need to know what speaker is correct for any model, we can advise you, and provide a photo as well if you need a better photo than we included in the Scott Collector's Guide, 2nd edition.

For your WR-10, here are a couplele  I have as examples:

The Tower Pirate Ship 14 inch:   IMG_1342.jpeg

The Tower Adventurer, 18 inch, illuminated version:  DSCF3516.JPG

[Mark Schroeder]

Greatly appreciate all the comments and details. Just had a Radiola 100A delivered and hoping its working. Other radios that I have that are missing original speakers are an Allwave 12 deluxe (with Wunderlich) and a Imperial 23 (always looking for a complete in cabinet 23 for the collection).

Now my next challenge with the Super 10 is building up a battery eliminator supply for it. I often wondered how they got 450V B+ from batteries. String together 5 - 90V cells? Have you seen anyone that has built one up that provides the B+ needed for the type 10 tube? Looks like some guitar amp transformers may provide what I need to roll my own. 

[Kent King]

Mark -

You really don't need the 450v supply for the Super 10. I run mine on a supply that provides up to 135v, and it works very nicely. You may not need to bias the grid on the 10 quite as much with a lower plate voltage. An RCA tube manual provides curves as guidance for appropriate voltages. I would recommend getting an ARBE-iii power supply (https://www.arbeiii.com/), they will handle most 1920s battery sets.

Kent

[Mark Schroeder]

Excellent recommendation. Just ordered one. Had seen these but the 450 was the high mark to get over. This is probably the only “battery” set I ever want to tackle. Looking forward to making it sing, while we still have AM stations running in the Phoenix area………