My new (vintage) Tannoy Cheviots!

[DSJR]

Sorry geoff, I meant the holes in the tweeter waveguide. PLEASE make sure the holes in the casting are even all the way round and properly profiled, as they look a bit rough from the angle of the shot you've provided.

I do envy those who take their own drive units to bits this way. Tannoys look to have been built with this in mind. My Spendor BC2 bass units apparently have an audible reflection between the larger diameter (compared to BC1) voice-coil centre dust covers and the pole piece and it's been suggested by a key chap at Spendor that I remove these dust-caps as done in the SP1 driver which was loosely based on the BC2/SA2/Prelude driver and fit a "phase plug" as Spendor now do I think. The doping on my bextrene cones is in pristine condition still and I'm absolutely terrified of tearing it in a botched attempt at removing the dust-caps..

[walpurgis]

The waveguide on Tannoys circa 1980 was not as well machined as earlier examples, but this does not seem to affect the sound.

Leave your Spendor cones well alone Dave! What happens to older Plasticote treated cones is that the slightest disturbance will cause the coating to lift and continue peeling. If you try to remove the dust caps you'll pull off the coating too.

The biggest problems the BC2 and BC1 had were the Bextrene cone 'squawk' (which KEF and B&W also had). On the Spendors it was not quite so evident though, its a colouration your ears adjust to anyway. And, there's a bit of port 'chuffing' at the bottom end at high volumes. I won't comment much on the awful Coles/STC/ITT super tweeter (it really is horrible sounding), other than to say, Rogers went to the wonderful Celestion HF2000 instead on their Export Monitor which was a closely similar design. Fortunately the super tweeter on the Spendors does not cover much of the audible spectrum.


Geoff.

[walpurgis]

This morning,

masked off the tweeter to prevent crap going in!



Slicing through adhesive and old surround under the rubber trim on the inner flange face.



One trim ring in perfect condition. It'll clean up well enough to re-use and now I've got to clean the speaker chassis inner flange face to accept the new surround.



I'm having a rethink on the surrounds. The mounting face on the speaker chassis is wider than anticipated and although the outer roll on the new fabric surround just clears, I don't want to risk the surround making contact during large extensions when driven. So, it looks like the poly/foam single roll surrounds may be used after all.

More later.

Geoff.

[walpurgis]

Latest.

One cone fitted with new surround. properly bonded under the bracing ribs which are now also re-bonded at their termination. No, the surround is not the wrong way round, its just the effect of the lighting.

The speaker chassis needs a bit more cleaning up, then the cone goes back in later today.



Dealing with the minor surface corrosion in the horn throat. Magnet gap masked and mouth of pepperpot wave guide covered with a dollop of bluetack.



The corrosion now gone. I rubbed it off with very fine emery paper and then wiped on acrylic laquer to seal the surface against recurrence. The corrosion left minor discolouration which is of no significance.





Note: never use wire wool, wire brushes or anything made of steel near speaker magnets. Any loose bits will contaminate the coil gap, etc.




More later.

[walpurgis]

Back on track at last.

After many weeks of delay and misfortune, two pairs of surrounds that didn't fit properly and waiting for suitable surrounds to come from Australia and then stripping off dodgy surrounds and starting to fit good ones, I'm back in action.

Below, new surround bonded to cone and cone spider centralised, blobs of blu-tak used to check that the cone will move freely and concentrically before glueing the outer edges of the surround into the speaker chassis, because once that's done there's no going back.



Next photo, the cone now fixed in place, with the circular edge trim fitted and the cone is moving nice and freely. With a bright torch I can see that the coil former is properly concentric to the horn/pole piece, no wedges were used. This driver is basically finished.



Now to start on the other one!

[realysm42]

Good work; how long has it taken in total?

[walpurgis]

Good work; how long has it taken in total?

You'll laugh Martin, I started in July, but had repeated problems with inadequate cone surrounds. Then I was on holiday for a while. When I got back I ordered good surrounds from Australia and they took nearly a month to get here. By this time I was getting a bit fed up and waited a few weeks to get cracking again, however all's going well now.

Another driver to overhaul and a bit of cabinet finishing to do. Once that's out of the way I may experiment with internal wiring and crossover components. Although to be honest when I bought these, I had a long demo (with knackered surrounds) and they sounded absolutely marvellous, so I don't think they are likely to need much enhancement and have to say the 3128 dual concentric drivers make these by far the best Cheviots I've heard, far smoother and cleaner than any HPD 315 I've owned and better even than my old 12" Monitor Gold Chatsworths.

Here's a shot of the unit I have to strip down tomorrow. It doesn't show you much, but the surround is truly stuffed!

[walpurgis]

Started on driver two this morning.

After insoldering the tweeter connection and unbolting the connector block and the rear cone spider. The point of no return arrives again, slicing the old surround so the cone can come out.



The loose cone!



Now I've got to spend a few patient hours stripping off the gooey remains of the old surround which even extends under the ends of the Girdacoustic cone bracing ribs.

[walpurgis]

As you can see, the remains of the old cone surround are just a sticky mess!

[walpurgis]

Finally got the second cone clean, it took literally hours to scrape the surround remains off. No wonder Lockwood only do whole cone replacements these days.

Sorry about the photo quality, must have forgotten the camera's 'macro' setting!



I've put the new surround in place, looks good, properly tucked under the bracing rib ends prior to gluing. That's the next job, I'll first bond the surround to the rib ends, that way its fixed in the correct postion for the rest of the gluing. Its how I did the first one and that was fine. I'm using 'Aleene's Original Tacky Glue', as many do. I apply it with a small art brush with the bristles cut down a bit.




And yes the surround is the right way up, its just the flash makes look wrong.


Later:



Surround glued to Girdacoustic rib ends, it'll have to dry overnight!

I've kept the cone face down as that pushes the surround upwards onto the ribs ensuring contact is maintained while it dries.

By the way, once its been drying for about an hour, turn the cone over and check that the crease on the surround lines up exactly with the cone edge, pull it into place if need be as the glue will still have movement in it, then press into place firmly.