Tannoy C-88 Twin Tweeter Transplant Step By Step

May 22, 2019

#310

Gentle reader,

I had finally, after 40 plus years in the hobby of home entertainment, especially music reproduction, gotten THE sound that I was completely happy with. Really.

And here it is. You can't see much of the components, but long time readers of my blog know what it contains. Speakers are Klipsch KG4s and Dynaco A25XLs. I vowed to buy no further equipment unless it was a bargain that I could pass on to another hobbyist via eBay. Plus Spring cleaning showed us that we should stop filling our house with other peoples stuff. So, we generally stopped going to thrift stores. In my case, great audio finds were few and far between, anyway. 

NOTE: If you are viewing this on a computer, clicking on any picture will open a second window over this one. You click through or use your right and left arrow keys to look at the photos. They will be larger than seen here. If you are viewing it on a device such as a phone or tablet, I do not know if that works the same way. 

After a stop to pick up some prescriptions, I asked Nancy what she wanted to do. "Thrift store?" "Savers or Goodwill.? She chose Savers. It was a wise choice. There, I came across a pair of black tower speakers. They were Tannoy C-88 models and at $24.99, and fully functioning, I could not pass them by. Plus, I have never owned any Tannoy speakers. This is the same store where I found the above KG4s albeit, they were then only $9.99. Oh, and it was obvious that all four woofers had already been refoamed. SCORE!

They sounded great, or so I thought. I had swapped them into the positions held by the A25XLs. Nice robust, well rounded sound. Right until I switched to the KG4s. Whoa! Those are some highs! Where the hell are the highs from the C-88s? 

I brought up my concerns to the various vintage stereo/HiFi Facebook groups I belong to. There was NO information on these Tannoy models on the Internet. And Tannoy's site has no information on older models. My Orion Blue Book of Audio equipment listed them as being built in 1991 and retailing for $800US or around $1,550 in 2019 money. Too rich for my blood. But for 25 bucks? Sold!

One person, sorry that I cannot remember your name, came up with the suggestion that I try a tweeter from another speaker. Brilliant! I pulled one from one of my Cerwin-Vega! LS-12s. I removed the Tannoy driver and plugged in the C-V tweeter. THAT'S what I'm talking about! Serious highs.

I then tried the Tannoy tweeter in the C-V, dull highs. OK, I have eliminated the crossover as the problem.  

Parts Express have some Peerless by Tymphany DA25BG08-08 1" Aluminum Dome Tweeter 8 Ohm for $26 and change, great! And they are 3.54". So I ordered a pair. And waited. Nothing. So, I contacted them, a very nice woman informed me that I had to order a minimum of 1000. So, those were out. Oh, the four ohm and 6 ohm ones are available singly. But I skipped them.

The Tannoy tweeters measured 7 ohms resistance and were 3.54" across. A search on eBay yielded me these MTX branded tweeters that are in fact Peerless units and made in Denmark, the same country that made Dynaco speakers.

$41.95 for the pair. They are slightly wider than the Tannoy's but have a nominal resistance of 6.8 ohms. Nearly perfect.

The following FOUR images are from the eBay auction from which I purchased these tweeters. Seller ID is: PUREWAVE. A link to their items is below:

Items for sale by purewave | eBay 

They are their images, but since I have now advertised their eBay page and am tickled pink with these NOS (New Old Stock) Peerless tweeters, I highly recommend that you too check out PUREWAVE on eBay.

Well, will you look at that, Made in U.S.A., hah! A sticker does not make it so!

These two charts are part of the auction's information. Pretty flat frequency response.

They have a decibel output of 91.2 at one watt or 2.83 volts in an anechoic chamber. Since I don't know the Canadian made C-88's efficiency, I hope that these are a little more efficient.

As you can see, the new tweeters are larger, this is OK as you will observe how I tackled that below.

"ROAD THUNDER PRO" what were they thinking? Thunder is not a high frequency sound. I never had any desire to own any MTX equipment, but since I have never heard any, I cannot judge them either.

Sadly, Peerless did not mark the polarity on these tweeters. I hooked them up the same way the old ones were wired.

I have a perfectly good metal calipers with a precision dial on them downstairs in one of the toolboxes. I never use them. These are right here in a pewter cup on my desk with the two pairs of scissors and a utility knife. So I always use the plastic ones.

Old opening is 2 7/8 inches. New drivers need one that is at least 3 1/8 inches. A minimum of 1/4" has to be removed.

I needed something to use as a template. I was almost done with a roll of clear packing tape, so I wound what was left onto a new roll and voila! A template that was a little big, but would do.

I carefully centered the empty roll and drew around it with a blue Sharpie as seen below.

Cutout was to clear the tweeter's terminals. Had it not been there, a router could have been used.

The two woofers in the first speaker were marked in red ink as to their location and possibly for polarity as well.
I'm not sure about the gold stickers nor why they are there. Perhaps they did the refoaming job? If so, their reinstallation of the front gaskets leaves much to be desired.

Not sure what TR refers to. The tweeters are not marked as to where they were made.

The photo below shows how the factory insulation has fallen from where it was once installed. That will NOT do!

I generally do not like crossovers that are incorporated onto the terminal cup. But at least they are proper three-way binding/banana terminals. It would be tough to read those capacitors since they are glued into the coil.

Longer pair of wires go to the top woofer. Below is the other side of the crossover.

I removed the collapsed insulation and the crossover/terminal cup. Below shows the two ports and the way they curved the insulation at the bottom.

I shall do the same at the top and middle sections when I reinstall the pieces. Set up properly, the bass waves should be routed to the reflex ports.

This is the finest saber saw we have ever had. It too was a thrift store find. Variable speed, easy insertion and removal of blades, on-board blade storage too.

Ideally, I wanted to stay to the inside of my circular line.

Above is the insides of the second speaker. Just as jumbled as the other one, insulation-wise.

As it turns out, I am not that skilled with a saber saw. The new tweeters have no gasket material on them. So I came up with the idea of putting a layer of clear RTV silicone glue around the opening and letting it cure.

I picked screws that were smaller in diameter since I needed to install them at an angle away from the hole's opening.

Once tightened, they were perfect. The cured RTV glue is compressed by the new tweeter and keeps those bass back waves inside the cabinet and routed out the rear reflex ports as they are supposed to be. 

These are the best staple guns I have ever tried. Instead of being hinged at the top/front and squeezing the traditional way, they hinged these at the back and one can apply more pressure to fire the staples. Plus, they also can shoot nails. Bonus!

Above is the middle section of insulation as seen through the lower woofer hole. There is a brace from back of the cabinet to front by the tweeter hole. See the insulation's curve? I used lots of staples and added Elmer's glue between the layers of insulation to keep it all together and in place.

Above and below are looking towards the top of the cabinet through the upper woofer hole. Nice curves, right? Who doesn't like nice curves?

Below is showing the transition from the reinstalled middle insulation to the bottom portion which I never removed.

Factory cut slit for the wires to pass through to the drivers in the insulated chamber.

First one is done! I chose Michael Buble's CD Call Me Irresponsible as it sound's great and I know what I expect it to sound like. I switched the preamp to mono and swung the balance all the way to the left. Oh, yeah! That's the tweeter sound I was missing.

I don't know what the person that did the refoaming was thinking when they put the front gaskets back on. But, having grandkids, I'm a grilles-on guy anyway, so I can't see them.

Both grille frames were broken when I found the speakers. That was the first thing I fixed on their path to wholeness.

And here is the final results. Because of all the other work I did to restore them internally and having to wait for the RTV glue to cure, it took about five hours total. I am very happy with the results. Perhaps, now that the insulation is back where it's supposed to be, the bass sounds better as well. 

Thank you SO much for taking the time to read my humble words and view my images. It is your kind words and encouragement that keeps me cranking them out.

Scott
May 22, 2019
#130