Restoring my OA12's

[Andy H]

Hi,

I am about to start restoring my Sonab OA12 speakers, which I bought from a friend around 1978.

Thanks to the excellent information on your website I have been able to locate a supplier for replacement speaker elements and also for the capacitors in the crossovers.
Before I get started I could do with some advice on the following issues:

I understand that the original bass/midrange elements were made in three different impedance’s 5.3 / 8 /16 ohms
The impedance quoted for the replacement unit is 8 ohms but unfortunately I no longer have the original SC165 drive units and cannot therefore check their impedance. Is it possible to determine their value from the following:

Cabinet Serial Number 13259
Cabinet Dwg Number 5-0 110 102
Crossover resistors 2.2 ohms (both)
Crossover capacitor 5.6uF
Crossover inductors – I have no means of testing

I see that the replacement tweeters require some modification to allow fitting – are there any drawings available of the mounting details?

One of the crossover inductor retaining clips and has gone missing as has the aluminium pin but I do have the Bakelite disc – Is it OK to re-fit the disc and clamp the inductor coil using any non-ferrous fastener such as a nylon or brass nut and bolt?

Are there any preferred solutions to the mounting of speaker terminals beneath the speaker?
I’m reluctant to start drilling an irreplaceable part of the speaker cabinet.
Any other tips specific to this model will be very welcome.

Thanks in advance, Andy

[Stefan Björklund]

Hello

All OA12 have 8 Ohm bass/midrange units...

The CT62 tweeters are the 16 ohm model...

Concenrning speaker terminals...
If you don't want to "harm" your babies you could glue a L-shaped bracket on to the bottom of the cabinet, (with a glue that could be disolved with some solvent) and mount terminal screws in holes in this bracket...

Regards

Stefan

[12björn]

with a glue that could be disolved with some solvent

...or heat, i.e. hairdryer, like SuperAttack ond other fastworking glues.

Björn

[Andy H]

Thanks guys.

I'm not totally against drilling the bottom of the cabinets and I suppose one advantage of bringing the connections in through the base is that you don't have to feed the cable up through the bass port. I just wondered which type of connector was considered best and where exactly to drill.

Thanks again, Andy

[stefanb]

You have to drill a hole exactly in the middle of the cabinet. I used a terminal with 50 mm diameter.  You also have to remove the old "bracket" with a knife or chisel. I have apicture of the result in this thread.

http://carlssonplanet.com/forum/viewtop ... ight=#5439

Stefan

[Andy H]

Brilliant!

I'll be going for the circular sunken plate method.

Wow, those restored OA12's with the silver/grey finish to the ABS mouldings and grilles look pretty darn fantastic!!

What type of finish has been applied and what preparation is required to make it bond to the plastic?

I wish I could speak (and read) Swedish.

Andy

[stefanb]

Hi Andy,

You are not the first one to compliment on my oak-veneered OA12. Thanks

I have described the work in another thread, unfortunately in Swedish, but with some pictures from the work.

http://carlssonplanet.com/forum/viewtopic.php?t=1153

My speakers had originally a jacaranda-veneer. I grinded it down a little bite before gluing on the new oak-veneer using standard PVA glue (the white stuff normally used for wood that get a more grey/transparent look when it is dry.

The baffle is painted with grey/silver aerosol spray, preferably done before you mount the new tweeters, and I used the same paint for the grill.

The rubber feet are masked with silver grey duck tape  :D .

Stefan

[Andy H]

Thanks to everyone for the advice / tips.

I've got as far as I can with the restoration for the moment as I am still awaiting delivery of the replacement speaker elements.

I have made the wooden blocks for mounting the tweeters from an old piece of oak that I had lying around. What is the best type of glue to use to stick the blocks to the baffle and for sticking the tweeter elements to the blocks?
I pressume a quick setting epoxy resin (Araldite) would be best.

Andy

[stefanb]

Andy,

Carlssonplanet recommend a glue named Tremco PL400. I guess it is available in England to, since I found it on Tremcos UK site: http://www.tremcoeurope.com/Toppage/homeset.html

I guess araldite will do the work too.

Stefan