KLH Model Eight Receiving System
"Lady Eight" A Classic
By Chris Jones
Figure 1. The KLH Model Eight consisting of a speaker and FM receiver. The receiver's four controls are, from left to right, power on/off, treble, volume, and tuning.
Anyone who grew up in the booming hi-fi days of the '50s and '60s knew the crisp KLH sound that permeated most shops of the day. Chris Jones writes about the very popular Model Eight, one of the first really small, self-contained table systems. (Editor)
While today we are accustomed to ever-increasing sound quality in ever-shrinking, and simpler equipments, this hasn't always been the case. In the golden age of high fidelity and stereo in the 1950s and 1960s, the hardware was generally complex, large, and heavy. The standard set up for audiophiles was a turntable and/or tuner, a preamplifier, a power amplifier, and a speaker or speakers, plus the attendant cabling.
The quality of the amplifier could be partially assessed by the weight, largely a function of the output and power transformers. The speaker quality was determined by the size of the woofers and number of pounds in the magnet. It was in this environment that Henry Kloss (pronounced close) and his firm KLH Research and Development Corporation of Cambridge, Massachusetts, brought out the KLH Model Eight FM Receiving System in 1960.
The KLH Model Eight
The KLH Model Eight (the number is always spelled out in company literature), shown in Figure 1, provided in two shoebox-sized cabinets, a sensitive and selective FM receiver with an excellent audio system, and a high quality speaker system. Operation was simple with only four controls: a power switch, a treble control, a volume control, and a vernier-drive tuning control.
Beyond the novelty of the small size was the innovation that the two units were specifically designed to work together and only together. The receiver's audio response was deliberately shaped to produce a pronounced bass boost to compensate for the limitations in the speaker's response resulting from its small size. The Model Eight was thus the forerunner of a number of well-known radio and audio products today that rely on unique combinations of shaped amplifier audio response and advanced speaker system design to achieve a symbiotic, superior overall result. This was certainly true with the KLH Model Eight. Contemporary reviewers favorably compared the overall sound to that of much larger and more complex systems with certain program material.
The receiver used seven tubes: a 6BS8 dual triode as a wideband RF amp and audio preamp; a 6U8A triode-pentode as the oscillator and mixer respectively; three 6AU6A pentodes as IF stages (the last one a limiter); and two ECL82/6BM8 triode-beam power pentodes in a push-pull power amplifier. A rear view is shown in Figure 2. FM detection was via a ratio detector with solid-state diodes. The internally-fused power supply incorporated a transformer and a solid-state rectifier.
The RF-IF tube lineup is very similar, if not identical, to a contemporary H.H. Scott receiver, as I recall from a quick look. A little reverse engineering by someone perhaps? (Now that I think of it, that vernier tuning knob looks kind of familiar too.) Both a tuner and a multiplex output were provided. Interestingly, the multiplex output had about 85VDC on it presumably to power what is referred to in advertising literature as an adapter to allow use of a turntable or tape recorder with the Model Eight's audio system. I have just seen a receiver with one of these (also referred to in a product review as a transistorized preamp) sold on eBay for a price well into Catalin territory. The preamp appears to be in a small metal case with about one-fourth the dimensions of the receiver.
Figure 2. This chassis view of the receiver reveals its compactness and simplicity.
The multiplex system was another pair of cabinets, electronics in one and a matching speaker system in the other. A February 1961 review in High Fidelity Magazine reported the sensitivity at 2.5 microvolts, and the power output at just over 3 watts into 16 ohms. The amplifier frequency response, based on my measurements, extends from 30Hz to 45kHz with about 6dB of boost at 125Hz.
The speaker used two 4-inch long-throw drivers with, based on advertising literature, what looks like very large magnets. These were packaged in an acoustic-suspension (essentially air-tight) enclosure with 30 feet of cable wound around two cleats on the back allowing remote location of the speaker. Based on the product review test results on the amplifier, I assume the overall speaker impedance is nominally 16 ohms. A rear view of the speaker is shown in Figure 3. Both the receiver and speaker enclosures were solid walnut. The price was $159.
Having used the KLH Model Twenty-One solid-state offspring (everything in one cabinet) for several years, I thought it would be fun to try to find a Model Eight. "Wanted" ads in ARC didn't yield anything within my price range, and watching the auctions on eBay was frightening both in the sale prices and the tactics of both some sellers and bidders.
However, one day the Web browser suddenly surfaced an over one year old posting on an audiophile Web site by someone casually inquiring if anyone wanted to buy his Model Twenty-One and Model Eight. An e-mail inquiry revealed that miraculously the receiver hadn't been sold, that he was the original owner, that he bought it in Cambridge in 1961, and that he would think about it.
Thus began about ten days of courteous e-mail traffic regarding what he eventually came to call "Lady Eight," with the end result that the amount of the dowry was agreed upon. Within less than two weeks since the first communication, the object of my affection arrived--his radio and my check having crossed in the mail.
The Poke and Peek
Lady Eight arrived apparently working fine upon first listen, with 40 years of family wear and tear and with all parts intact save an antenna terminal nut, a small antenna-related connecting strap, and the original speaker plug. The receiver and speaker serial numbers are identical -- 1210. I get the impression that, like buying a classic GTO, it's more desirable when all of the part numbers match, showing that the radio and speaker were originally together. I've seen receivers for sale without the speakers, with non-KLH speakers, and one person auctioning the receiver and speaker separately.
The seller reported that the radio had been serviced by KLH around 1970. Apparently this service was required for replacement of the multisection power supply cap, which looked replaced. Also, someone had made a pen-and-ink change to the schematic attached to the cabinet bottom, reflecting a change in value (down) and rating (up) of one section. Either KLH guarded its transformer designs closely, or its supplier was worried about being second-sourced, as the output transformer is potted, and the screws holding the end bells on the power transformer have the Phillips heads filled with epoxy.
Electrical checkout revealed that all the tubes were strong or at least adequate. Several tubes were made by Raytheon, and since that is a Massachusetts company also, I assumed these were original. While one tube showed jaundice, reading in the yellow "weak" or questionable area on the dynamic transconductance tube tester, I've adopted a policy of not re-tubing unless tubes read really low (except output tubes), as I'm not sure it will make a difference. I could hear, and so better to leave the increasingly-scarce tubes in the marketplace for people who have truly dead ones, and, of course, save money to boot.
Further listening and testing revealed excessive hum from a badly decreased-in-value filter capacitor section in the previously replaced capacitor, a burned decoupling resistor, and a KLH-induced bad solder joint in the filament wiring that started showing up as intermittent loss of one ECL82's filament. Most exciting of all was an apparent KLH-original inadvertent short of one AC input line to the chassis.
Figure 3. This rear view of the Model Eight's speaker shows its nameplate and cable holders. The original connector was a one-piece dual banana plug.
Model Eights may be slightly more susceptible to hum as they age due to the previously mentioned DC on the multiplex output. This has the effect of connecting the B+ (with any ripple) directly to the most sensitive point in the audio chain. I noted that a High Fidelity Magazine review commented on the hum level as if it was a little unexpected but not objectionable. In any case, correction of these problems was followed by complete realignment, the ritual pot spraying, one week of occasional operation on the bench just to be sure, and she was all ready.
Or so I thought until, after one week of completely reassembled use in the den, the bony hand of Capacitus the Confounder reached out in the form of the bane of all people who work with electronics -- a temperature-dependent problem. In this case, it was a suddenly varying audio level, but only after running for an hour or two. Bringing wires out of the cabinet attached to various places I thought could cause such a symptom. Allowing the receiver to reach maximum normal temperature ultimately revealed that the problem was due to a bad stabilizer capacitor in the ratio detector.
Cosmetic work consisted partially of the usual cleaning of chassis, woodwork, knobs and other typical things. In addition, Model Eight knobs are retained by a type of cantilever spring clip that I can't recall seeing before. My clips needed to be bent to restore their grip and prevent their rotating slightly when the related control was turned. One clip was broken, requiring use of a small flat nylon spacer for a tight fit. I've seen Model Eights for sale with missing knobs so this may also be a typical affliction. The vernier drive tuning while having slight play showed no signs of slippage.
The receiver cabinet top has a split the entire length that isn't disfiguring enough to require action, at least to suit me. I've also seen this on at least one other unit so I assume this may be typical and due to repetitive heating and cooling, possibly in those cases where the owner put the speaker on top of the receiver, undoubtedly raising the case temperature.
The only really unusual defect was a bad abrasion on the grass-cloth-type speaker grille that left a long, wide, very white mark. The solution turned out to be a trip to the art supply store where an artist's ink marker in a shade close enough was found to color in the blemish. A final touch in this area was a person selling a Model Eight on eBay who graciously sent me a copy of both his owner's manual and original advertising brochure--for free!
Lady Eight -- A Happy Woman
As mentioned earlier Lady Eight is a sensitive and selective receiver. It picks up a Toronto, Canada, station across Lake Ontario between two stronger local Western New York ones with only the line cord antenna,while yielding excellent audio quality. Warm-up drift is relatively low, thanks to the careful individual temperature compensation of each receiver. The Model Eight's three watts of audio power is plenty, with the treble clear and the bass, while not overwhelming, adequate and tightly controlled. She's a very pleasant radio to listen to and hopefully has another forty good years ahead of her with me.
High Fidelity Magazine, "KLH Model Eight FM Receiver," February, 1961, pp. 54-55.
KLH Model Eight FM Receiving System, advertising brochure, KLH Research and Development Corp, date unknown.
The New York Times, February 5, 2002. "Henry Kloss, 72, Innovator in Audio and Video, Dies.'
(Chris Jones, 38 South Ridge Trail, Fairport, New York 14450)
Chris Jones is an electrical engineering director and has been interested in old radios since he was offered a Westinghouse Aeriola Senior nearly twenty years ago. He tries to limit his acquisitions to only those that he can use periodically in normal everyday living and lately tends toward those things he remembers from his younger days but couldn't afford.
Henry Kloss, who died in January of 2002 at the age of 72, was renowned in the audio field. He cofounded Acoustic Research, KLH. of course, Advent, and Cambridge SoundWorks. He was also one of the inventors of the acoustic suspension speaker, brought out the first cassette deck with Dolby B noise reduction, and was a pioneer in projection television. Henry Kloss received an Emmy and was inducted into the Audio Hall of Fame and the Consumer Electronics Hall of Fame.