Some time ago I posted about GEC models BCS 2370 and 2373, and how they were essentially the same design in different body shapes for different applications.
Left to right – unknown, unknown. GEC BCS2370 and 2373 mics. All have the same motor.
Since then I have come across some other ribbon microphones which may be earlier GEC models, prototypes. They are perhaps rather ugly in style, but I find their functional utilitarian style rather charming.
The two unbadged mics share some parts including a twinaxial connector at the base and rubber yoke mounts. The mic on the left is made of folded steel, whereas the one on the right is brass, with a more open grill.
All four mics are essentially the same design inside. The mic on the far left has a smaller transformer and different brand of magnet, but the pole pieces and ribbon assembly are the same. The mic in the middle of the photograph above is identical inside to the known GEC mics – with the same magnet and transformer and crumbling plastic ribbon mounts.
Remarkably, both of these mics are still working with a nice tone, although a little noisy. A good clean and service should sort that out.
Drawing from a ribbon mic patent by GEC and Thomas Julian, 1947
Which in turn is obviously inspired by the BBC-Marconi type AX ribbon mic…
Drawing from BBC-Marconi type AX ribbon mic manual.
As an aside, the GEC patent is slightly odd, in that the major innovation is that the pole pieces are held in place by the magnetic field alone, with no mechanical fasteners. That is to say the major innovation is something that they have left out, rather than something they have added to the system. The implication being that other manufacturers MUST use a screw, bolt or other fastener, or else risk infringing the patent. It would have been interesting to see how that one would stand up in court!
We’ve had some website issues this weekend, but everything has been sorted out, so let’s get back on track with another vintage microphone curiosity.
This gigantic bronze dynamic mic has no badge or makers name on it, but arrived in a box of GEC microphones. Connection to the outside world is made via two terminal posts at the rear. From the size and style it probably dates to the 1930s or even earlier.
It is around 11.5 cm across and 8.5 cm deep, weighs nearly 2 kg, and would originally have been mounted on springs within a hoop. Two of the suspension mounts are missing – it will be a quick job on the lathe to turn new ones from a bit of brass.
Inside the mic is very much like a speaker in reverse, with a paper and fabric cone driving a coil into the field of an enormous magnet.
On initial testing, the mic wasn’t picking up well as the cylinder in the centre of the diaphragm was scraping against something as it moved. Some careful cleaning to remove the dirt eased the movement, and the mic sounds OK, if rather peaky. The addition of some foam inside the body helped to dampen some of the ringing from the cavity.
Even with the foam, the mic is far from flat in response with an enormous bump at 200Hz. So if you want to give something an EQ boost at 200Hz, this is your mic!
Frequency plot for big bronze dynamic microphone!
Other uses include door stop, paperweight, shot-put and burglar deterrent (ouch!).
If you recognise this one or have information on any of our other unidentified mics, please get in touch.
This pair of rather handsome ribbon microphones by General Electrical Company are our microphones of the month for July & August.
The mic on the left is labelled with the model number BCS2373, and was the ‘studio’ model, with a single layer mesh grill, and thumb screw terminals. Like many early studio ribbons, this one has a 30 ohm output impedance.
On the right is the 2370, with a more robust housing and a curved body. These were probably used as ‘lip’ microphones for sports commentary and broadcasting in noisier environments. Indeed, one of our customers sent in a very nice example that came complete with its original handle.
GEC 2370 with handle
These mics were available with different output transformers for different applications. I’ve seen two examples of the 2370 – one had a 10K ohm output, the other measured 600 ohms impedance.
Although they look rather different from the outside, they are twins under the skin – both have identical motor assemblies, with cylindrical pole pieces attached to a large horseshoe magnet, held in place by the magnetic field along The design of the microphone is described in this patent from 1947. All of the GECs that I’ve seen have held their magnetic field well over time. The only real differences between these mics are the output transformer and the body.
As usual, after all these years they benefit from a good clean and a new ribbon. Particularly as this one arrived with a ribbon made from a fag-packet! Both mics are now working well and should provide some good service for years to come.
* Thanks to Santiago Ramos for additional information.
Addenda – one of these came up recently for sale complete with original box. The owner was kind enough to share this photo of the label.