Disassembly
You've decided to repair some damage, or refurbish the whole speaker, but first(!) you need to take it apart, properly...

You've decided to repair some damage, or refurbish the whole speaker, but first(!) you need to take it apart, properly. Take it easy, since anything you damage is likely to be expensive or time consuming to fix, or both. Even the BA-type screws will be hard to replace if you lose them, so be tidy and careful with all the old parts. This section will explain how to take the speaker apart with the minimum fuss and bother.

 

WARNING!!

If you have not already done so, First Read...

Inspection

 

Grille Removal:

The front grille is removed as follows:

  • Remove the three screws retaining the side rails, along with their washers.
  • Remove the staples that hold the grille to the wooden frame at the sides.
  • Remove the 10 to 12 small wood screws from the front bottom edge (underneath) of the front grille.
  • Carefully lift the grille in a smooth arc, forwards and outwards, being patient at all times lest you bend the grille (it's only expanded aluminium)

The rear grille is removed as follows:

  • Remove the twenty, or so, small wood screws around the periphery of the wooden frame at the rear, along with their washers.
  • Remove the rear grille, being careful not to puncture a dust cover or yourself!

 

EHT Block Disconnection:

To disconnect the EHT block, do the following:
(all directions as viewed from the rear of the speaker)
(The speaker must be off for at least 2 hours!!)

  • Place a stiff piece of cardboard, or a rolled up cloth, between the EHT block and the bass panel to prevent any solder melting the dust cover, or worse.
  • Using a standard 20 Watt iron, de-solder, from left to right: the thick red wire, the thin red wire, and the thin black wire. This disconnects (physically and electrically) the bass panel 6kV line (thick red), the treble panel 1.5kV line (thin red) and the Ground/Earth wire (thin black) to the audio transformer.
  • Do not disconnect the other wires on the EHT at this time, they only connect to the mains transformer, which is physically part of the cage assembly on which the EHT block is fixed. You will be able to remove all the large assemblies with these latter wires in place.

 

EHT Assembly Removal:

(all directions as viewed from the rear of the speaker)
(The speaker must be off for at least 2 hours!!)
To remove the Mains Transformer cage and EHT unit (on top) from the frame, do the following:

    • Locate the four (4) retaining bolts under the right, rear of the frame and unbolt them. These bolts do have nuts above the frame, which may need to be held with a spanner or pliers.
    • The Mains Transformer cage and EHT block can now be completely removed from the speaker.

 

Audio Transformer Disconnection:

(all directions as viewed from the rear of the speaker)
(The speaker must be off for at least 2 hours!!)
The audio transformer is the large 'can' on the left, rear of the speaker. To remove it, and disconnect the treble and bass panels, do the following:

  1. Place the speaker on a stand, or up on two bricks, or whatever, so that you can easily work underneath it without grovelling on the floor too much.

  2. Find the four large bolts (pan head) underneath the left side of the speaker that secure the audio transformer.

  3. Remove these bolts. There are no corresponding nuts. The bolts screw into tapped brass blocks mounted inside the audio transformer. When the transformer comes loose, be careful it doesn't slide about as it is very heavy and can damage wiring and panels.

  4. Turn the audio transformer (carefully!) upside down. This requires some fiddling about because of the restricted wiring loom, but it can be done. There is just enough free play in the wires. You should end up with the audio transformer sitting in its usual spot, only upside down.

  5. Now, examine the underside in detail. If you see a whole lot of bees wax (brown/yellow gunk) then this device has never before been touched since it left the factory. You will see several wires entering through a rubber grommet at the front of the transformer housing. The thin brown and blue wires go to the front and rear plates of the treble panel. The brown wires connect to the centre strip and the blue wires to the other two strips in the treble panel. The thick white and black wires take audio signals to the bass panels. A schema of the underside of the audio transformers of each type is shown below:

  1. De-solder the wires from the solder posts, and remove them carefully through the rubber grommet. At this point, you will be able to take the heavy transformer unit out of the frame, and give yourself more room to move. You may need a hefty soldering iron for this this - about 40 Watts should do.!

  2. Take a very careful note of each wire's position. If you cannot read this simple schema, or you don't trust yourself to remember the wiring pattern, then LABEL each individual wire, and where it goes with a stick-on tab, or something. Colour code them with permanent marking pens, and write down the colours would also work well. If you re-wire incorrectly, the speaker will: run out of phase, not run at all, emit smoke!

 


End Note: If, for any reason, you need to remove the bees wax, then use a heat gun. I use a 1600 Watt variable setting gun that can be set as low as 400 Watts. This gives a lot of control, since you can keep the gun moving!!

 

Treble Panel Removal:

(The speaker must be off for at least 2 hours!!)


To remove the treble panel, do the following:

  1. Double check that the thin red wire to the EHT, the two thin brown, and two thin blue wires to the audio transformer have been de-soldered.

  2. The thin red wire needs to be pulled back through the frame supports (large inverted V-blocks) to the audio transformer side of the frame.

  3. Now go to the front of the speaker, and you will see an aluminium retaining bracket between the two bass panels at top and bottom of the treble panels. These are folded aluminium of about 8 gauge. They are in the form of a U-channel, and if you look down into them you will see the heads of a couple of wood screws. Remove these screws.

  4. Remove the two aluminium brackets, top and bottom. This may require gentle(!) leverage with a screw driver. The panels are now mechanically unrestrained, but they will sit where they were put all those years ago.

  5. Move to the extreme right hand side of the wooden frame and insert a suitable flat bladed screwdriver blade between the wooden frame of the speaker and the bass panel frame. Gently lever the bass panel towards the centre. You will notice that it slides out of a couple of other aluminium brackets towards the edge of the speaker frame. It is not necessary to touch these brackets.

  6. Do the same to the other bass panel. The aim is to have them both loose, not removed from the frame at this stage.
  7. Set each bass panel at a slight angle to the treble panel, like a pair of opening doors. N.B. The panel dust covers may be stuck together after all this time under pressure - lever them gently apart.

  8. Now you will be able to remove the treble panel carefully, with its associated loom of wires, from the front of the speaker.

 

Bass Panel Removal:

(The speaker must be off for at least 2 hours!!)
To remove the bass panel(s), do the following:

  1. Do not remove the wiring from the frame unless you intend to totally rewire the speaker, or you are going to re-spray the wooden frame - this saves time and effort. These instructions simply cover the removal of the bass panel(s).

  2. Label the wires you remove! The order of the wires, as viewed from the rear is: BACK of Bass panel is connected to the thick white wire on the LEFT post; FRONT of the bass panel is connected to the thick black wire on the RIGHT post; and, the 6kV EHT line (thick red wire) is connected to the CENTRE post.

  3. Place a piece of cardboard between the small phenolic connection board and the plastic of the dust cover, to protect against blobs of solder melting their way into the panel.

  4. Using a standard 20 to 30 Watt soldering iron, de-solder the three wire at the bottom of each bass panel. You will find that with an original panel the wire was wound around and around and around....the post several times to get the smooth connection needed for the high voltages involved.

  5. Do not attempt to de-solder wires from the actual panel itself at this time. This is a delicate task, and will be described elsewhere. At this point you should be able to manoeuvre the bass panel(s) completely free of the frame.