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MG MGA - Radio Speaker size

Hi all.

I am in the last stages of putting the MGA back together. What I don't have and have not been able to find is the speaker size necessary for the speaker grille in the centre of the dash. I have looked at Barney's site and found the template for the fiber board mounting, but I am confused about what size speaker fits in it.

I have the radio that looks like a Motorola 406, but speaker is gone.

I would really appreciate knowing what size speaker will fit in the mount behind the dash.

Thanks.
CR Tyrell

Last time this came up was about three years ago, resulting in a couple new web pages. See here:
http://mgaguru.com/mgtech/accessories/at112c.htm
http://mgaguru.com/mgtech/accessories/at112d.htm

Today I got motivated enough to expand the original drawing to show formed up views of the folded card stock bracket. See attached images. Dimensions are on the above noted web pages.




Barney Gaylord

Thanks again Barney. I made a cardboard mock-up template from your drawing. I did miss the dimensions for the speaker. Looks like a 6" speaker will do the trick, and those are fairly easy to find.

Thanks again.
CR Tyrell

Several years ago I picked up an original loudspeaker 'box' but I couldn't find any information on the spec. of the original speaker. There is a picture in Clausager but you can't tell even the shape of it let alone the size.

So I studied the 'box' which is stamped out of 1/8" millboard and there were two features that I thought could give a clue to the speaker:- 1. the speaker fixing holes were punched out of the board and distance apart of these holes (along the board) was 5 1/8". I wondered why they had made it this odd dimension (why not 5" ?) and I concluded this must have been the fixing hole spacing of the original speaker. 2. there was an unusual flap about 5/8" wide at the rear of the box which was meant to hinge and was a bit of a puzzle but obviously meant to do something.

On the first point I started to look on Ebay for loudspeakers with a fixing hole spacing of 5 1/8". I didn't know whether the speaker was circular or elliptical but judging from the shape of the aperture in the assembled 'box' it seemed likely that the speaker shape was meant to be elliptical. There seemed to be many 8x5" speakers cropping up on Ebay but their hole spacings were always less than 5" and for the next size up viz. 9x6" the spacing was too great. I didn't come across any circular speakers with this spacing so I was on the verge of giving up when a speaker came up described as 'approximately 8x5'. When I enquired the size was around 8 5/8" x 5 5/8" and the hole spacing was 5 1/8" x 5 1/8" (slotted in one direction).

I bought this speaker and found that the unusual size was because it was based on an 8x5" cone size. The make of the speaker is ELAC and in the 1950s this was a small loudspeaker company based in London just a stone's throw away across North London from the Radiomobile factory. It is known that original factory fitted radios were all Radiomobile.

When I fitted the speaker to the box the reason for the 'flap' became clear. The flap was to cover the protruding part of the speaker at the rear end. I doubt if this was to improve the sound but rather to protect the exposed cone at the bottom.

I've fitted this speaker to the car and it sounds good. It was a bit of a struggle to fit it and it would be much easier to do it before the dashboard is fitted. The top front of the speaker comes very close to the scuttle but I noticed that there was an elliptical piece of the top hat section at the top of the scuttle cut away otherwise it wouldn't have fitted. This cut away piece was so well done that it must have been cut before the car body was made.

This size of ELAC speaker appears to be quite rare and it is the only one I've seen in four years of looking on Ebay. ELAC also do a standard 8 x 5" speaker with the wrong fixing spacing.

One other point about the loudspeaker is that it must be of the correct coil impedance to match the audio output stage of the radio. I believe all the Radiomobile radios required a speaker impedance of 4 ohms. I remember during the 1950s that common speaker impedances were 3, 5 and 15 ohms so either a 3 or 5 ohm impedance speaker would be suitable but with a 15 ohm speaker the sound volume would be affected.

I have some pictures and the first one shows the flap on the 'box'

m.j. moore

One showing the front.

m.j. moore

A side view.....

m.j. moore

View from the rear...................Mike

m.j. moore

Great stuff Mike! I will be looking for a speaker next. Used to be all kinds around, now not so many. I don't need a pair....lol.

I looked for the ohms req. for speaker on the radio... couldn't find it. Does anyone know Ohms for Motorola 406 radio?
CR Tyrell

Hey Colin,
You can get all the info on that radio at " radio museum . org"
It was a 1959 model and usually 6 volt.
If you find a speaker with a little higher impedance you should be safe. 8 ohms and 4 ohms are the most common now days. Maximum power transfer is probably not that important in the dash of a MGA at road speed.
Don
D Hanna

Thanks Don. Electronics is not my thing, but, I know enough to ask. I will look at that website. No doubt the radio will only be used when not driving,,,, can't see it producing enough sound when driving.
CR Tyrell

After using Barneys CAD drawing for the speaker enclosure and a trip to the craft store for some foam core and purchasing a 5x7 speaker, I finally got the radio and the speaker installed behind the dash. The speaker was $4.99 and fits perfectly. I just did not pierce the holes to mount the speaker until I got the speaker.

One thing I have found is the antenna is loose in the socket. It seems the antenna connection size has changed over the years. Once I pulled the antenna out of the connection and it made connection everything works fine. I think I will wrap some copper wire around the antenna connector and solder it up to increase the diameter. Has anyone found that this would be a problem?

The radio has no markings on it at all. It is made in Canada, and looks like the Motorola 406 found on Barney's site. 2 knobs and push buttons with the face plate that has "All Transistor" and BMC on it. It is also switchable pos./neg. ground and 6/12 volts. I have never seen another like it.
CR Tyrell

This thread was discussed between 25/04/2014 and 28/04/2014

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