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"Rare" KLH speaker: Model 708


JKent

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"Rare" in quotes because this is the ubiquitous 4" single-driver speaker that was marketed as a Model Twenty-One extension as well as being the stereo speakers for the Model Eleven-W and others. But the 708 has a couple of differences:

  • The model designation. It uses numerals instead of being spelled out and where did 708 come from?
  • The connectors. All other versions of this speaker (AFAIK) used RCA jacks. This has screw terminals.
  • The grille. All others have a flat fiberboard panel with cloth or vinyl covering. These have an odd "bumped out" grille that consists of cloth over brittle perforated plastic.
  • Biggest difference: The 708s have an LCR EQ circuit. All others are just run flat-out.

I've found virtually nothing about these speakers beyond a few comments on forums and a blurry scan of an ad (attached).

For the restoration I replaced the 150uF Callins PVC cap with a new Bennic NPE of the same value (but higher voltage rating).

The grilles proved to be a pain. The cloth was kind of ratty so I tore it off to reveal plastic panels that look virtually identical to the ones used on Allison speakers. I tried installing the plastic grilles "naked" but they were too transparent. Then tried gluing cloth to them with Aleene's Tacky Glue but they looked, well, "tacky."

Think I'll just make new flat panels out of 1/8" Masonite, like the Model Eleven-W etc. and cover them with speaker cloth. I have some salvaged from some no-name monkey coffins that has an authentic look. Will post a photo of that when finished.

Photos of the original grille, with and without original cloth, attached.

Kent

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post-101828-0-20011500-1406489513_thumb.

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It's amazing to me how much mileage KLH got out of the lowly 4" speaker. AR didn't even bother.

Those grille bases look like punched metal, and from the ad, I think they'd look pretty good.

I've seen this speaker auctioned a time or two, but not much else. Nice work, as usual.

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Thanks. Yes, the grilles "look" like punched metal. Wish they were. They are plastic. Possibly polystyrene, very much like the fragile grilles on Allison speakers.

The lowly 4" did get a lot of mileage. As I'm sure you know it first appeared as the replacement for the dual 3" speakers in the Model Eight speaker, also was used in all 5 versions of the Twenty-One radio and was the midrange in the Five and Twelve. It's been compared to the highly regarded Fostex 4' (forgot the model #).

The biggest surprise in this speaker was the EQ or filter network, not present in other versions of this speaker. Maybe compact systems like the Eleven-W incorporated that EQ in the amp circuitry. Just a guess.

-Kent

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Not hard to imagine an EQ in the amp circuitry after looking at the boxes wired to the Twelves.

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