Auster 隨手亂彈

The KT-1000 has one RF stage, as do the KT-3300D, L-02T and L-1000T. The L-1000T lets you bypass the single RF stage, as do the Onkyo T-9090 and Rotel RT-990BX (which is the same as the RHT10). The L-02T is double-tuned at the antenna and quad-tuned after the RF. The KT-9XG, KT-1000 and KT-3300D, like the Pioneer F-91 and F-99X, Sansui TX-701 and Yamaha T-70, are only single-tuned at the antenna and are double-tuned after the single RF stage. The KT-3300D, L-02T and L-1000T have passive mixers for improved IP3 [third-order intermodulation] rejection, at the cost of sensitivity. Double- and triple-tuning also costs sensitivity since these have bigger losses than a single-tuned circuit. The Kenwood 600T and 650T, KT-7000, L-07T and L-07TII have two RF stages. So does the KT-917. The same can be said of the Sansui TU-9900 and TU-X1 and the Yamaha CT-7000, which have two RF stages while those companies' later designs do not. Note that the number of gangs can get to as high as nine with a single RF stage, so it is not an issue of lower cost by going to a single RF stage.

Kenwood Basic T1 (1982, $200)
You have to wonder about eBay sellers who say the Kenwood Basic T1 tuner is "top of the line," because one look at a photo of the T1 will make it obvious that it's not exactly feature-packed. Our panelist Ray got a T1 to play with and was underwhelmed, finding "nothing inside": "I searched and searched and found no more than 5 varactors total, 3 for FM and 2 for AM. Two ceramic filters for FM, one for AM. The FM RF stage is enclosed in a walnut sized box and though the spec sheet claims 0.95 μV sensitivity, the actual performance does what the contents would suggest. No signal level indicators but there's a stereo light AND a mono light! LA3350 MPX, no buffer." Our panelist Bob says that the Basic series "was a retro line of components in response to the all-electronic pushbutton volume and tone controls offered by many Japanese companies in the '80s and later." The Basic T1 usually sells for $10-30 on eBay, with an inexplicable high of $75 in 2/04.

Kenwood Basic T2
Unlisted in the Orion Bluebook, the quartz-synthesized Basic T2 is a mystery to us, except that it's clearly a far better tuner than the Basic T1. We've just learned that it has Wide and Narrow IF bandwidth settings for FM, as well as an unusual adjustable slider control for variable IF bandwidth on the AM band. It uses Kenwood's "DLLD" (Direct Linear Loop Detector) technology, their name for a PLL detector, that can also be found in the KT-3300D and KT-5020, among others. Our panelist Bob says, "The Basic T2 came after the KT-9XG, which has a very similar, if not exact same, signal meter display. The T2 appears to be the first Kenwood tuner to use the DLLD. This was a big change point for Kenwood, as the KT-9XG still had the Pulse Count Detector." Our contributor Keith lauds the T2's "excellent AM section, very immune to interference/static." The T2 turns up on eBay occasionally and usually sells for $20-65, with a wacky high of $129 in 6/07.

Kenwood KT-9X
Here's our panelist Ray's review of this scarce tuner, which can be found with a silver front panel or a gold one, as the KT-9XG: "The KT-9X is an early Kenwood digital tuner. Circa 1981, it seems to fit between the end of Kenwood's analog thoroughbreds of the 1970s and their mass-market mediocrity of the mid 1980s and beyond. Fortunately, the KT-9X's bloodlines are much closer to the former than the latter.

"The front end is quite unique as it sports 5 FM gangs but two of them are in the local oscillator circuit as the LO is double-tuned and buffered. RF-wise it has the usual single tune, FET amp, double tune, mixer line up. BUT! There is a front-panel selector for RF mode. Normal mode is as described but direct mode bypasses the RF amp, leaving a triple tuned - mixer setup. This drops the sensitivity about 15 dB, giving the front end high selectivity and resistance to overload. Great for the urban dweller. The IF stages are Wide/Narrow selectable with two 250 kHz GDT ceramic filters in Wide and two 220 kHz CFs put between them in Narrow. Further on is the Kenwood quadrature pulse count detector and the well-regarded HA11223W multiplex chip. Audio out is IC buffered and there is active LPF filtering. All this adds up to a very good performing FM tuner. As a bonus the Wide/Normal bandwidth selector also affects the AM band, giving it better than usual performance. Even the power supply is special, with a separate transformer powering the digital circuitry to keep that potential noise out of the signal chain.

"The specs are good in all aspects. Note that the narrow IF selectivity is only rated at 65 dB, but this is at 300 kHz rather than 400 kHz as is normally the case. Subjectively RFM found the KT-9X to have exceptional sensitivity in normal RF mode and to sound very good without any mods. Though it shares much audio circuitry with the KT-815, it has a much better PC board layout, with short audio circuit traces, which may be the cause of its improved sonics. There is much to like about Kenwood's KT-9X except its rarity." The KT-9X and KT-9XG usually sell for just $10-50 on eBay.

Kenwood KT-80 (1980, $209)
Here's our contributor Stephan's great writeup: "The KT-80 is a no-nonsense FM-only 4-gang, 3-filter analog slimline tuner (3" high) that was the least expensive Kenwood with a pulse count detector. It was available in either silver or black (KT-80B) and featured few controls: power switch, tuning knob (nice size and weighted), rec cal tone, combined stereo and auto-muting, AFC, that's it. Two ordinary RCA jacks are used for audio output, the then-usual 75 and 300 Ohm screw terminals are provided for an antenna, and my 'E' model also features a coaxial 75-Ohm jack. Indicators are limited to stereo, 5-element signal strength and tuned/lock (the latter is brighter if the AFC is locked). Interestingly, what you see from the front are the ends of clear plastic 'light ducts' that are lit by LEDs on a PCB further up. The switches are made of the same material, which mostly serves the purpose of looking gimmicky. ;) The power switch also is illuminated, though on my sample the bulb - 8 V 50 mA, the only one in this tuner - is burnt out. A printed-on tuning scale with coarse marks every 500 kHz and fine marks every 200 kHz is provided, which unfortunately isn't too easy to read in the dark (reflecting some light from the dial pointer tends to give sufficient lighting of nearby MHz marks, but that's not ideal of course).

"Upon opening, the case didn't make the most robust impression, but it's the stuff inside that counts, isn't it? Sound and reception-wise, I'm quite pleased with the KT-80 on a dipole. It has good sensitivity, good 300 kHz and still-OK 200 kHz selectivity (non-Euro/UK models will be worse), and generally very clean audio with low noise, certainly in part thanks to the pulse count detector. Alignment isn't very far off, which I was pleased to see since the Grundig T-7000 it replaced (admittedly not a high-end model in its day) had drifted out of alignment pretty badly in spite of being a few years newer. There also is very little temperature-related drift. I noticed that with the AFC on there seems to be somewhat more bass. Given that alignment of the quadrature coil may be a good bit less than perfect now, I prefer to leave the AFC off.

"Going through the schematic, we can see that the KT-80's interior connects the FM sections of the earlier KT-615 and later KT-900, while being simplified only in the IF section. A 4-gang front end in the usual configuration with a dual-gate MOSFET as RF amp (no AGC in sight) is provided, with an air cap that shows gaps where two AM gangs would have been. An IC called SC114 is used as first oscillator and mixer. Overall, the front end is almost identical to the KT-900's. There is only one IF path which uses a total of three 3-pin ceramic filters with IF amps (discrete and TA7060P) in between, with two different (presumably matched) filter sets being used: The Europe/Scandinavia (E) and UK (T) versions used a 230 kHz GDT filter (SFE10.7MM) and two ordinary 180 kHz ones (SFE10.7MS3), while the rest of the world got a 180 or 150 kHz GDT filter (SFE10.7MZ1/2) and two 280 kHz GDT ones (SFE10.7ML) - the latter configuration would give better sound but worse selectivity and sensitivity due to higher losses. A HA1137W follows which provides additional amplification and an output for the signal strength indicator, an LC discriminator for the AFC is attached here as well. Following this there's the second mixer (presumably to a second IF of about 1.9 MHz) using an AN610P IC. Some filtering later you find the pulse count detector using a proprietary (and consequently undocumented) TR4010A IC which is also found in the KT-615/815. Another filter, the rec cal switch and the muting transistor (controlled by an AN6135) later we find the HA12016 MPX (also used in the KT-900). Behind that is a de-emphasis network (switchable de-emphasis is provided for worldwide models), a pilot tone filter (two adjustments per channel, presumably controlling notches for 19 and 38 kHz) and not much else - there is no dedicated output amp (KT-615 and KT-900 don't have one either). The AN6551 dual op-amp is used for AFC and rec cal tone instead.

"Interestingly, the KT-80 service manual and accordingly its specs are based upon the European 'E' model, while for the KT-900 (and presumably KT-615) it was the US 'K' model. Thus the specifications of the two models cannot be directly compared as the IF filters used differ and distortion, selectivity and (due to insertion loss depending on filter models) sensitivity will vary accordingly. A note on the power supply: Only the European 'E' and the UK 'T' models appear to have used a primary-side fuse in the power supply (for 220V: T63mA). It may not be the worst idea to install a fuse holder and fuse in other models when you're working on one anyway. (Check your current local safety regulations if in doubt.)

"As in many vintage tuners, the audio path can be shortened - if you can sacrifice the calibration tone and muting, a direct run with good coax from FL3 to the MPX would be possible (you'll need to use a coupling cap - e.g. 105/225 63V 1050 or 3.35 film and remove C33 and C40), and the overly long PCB traces from resistors R39 and R40 to output coupling caps C51, C52 can also be shortened. One would need to check whether C51 and C52 can be omitted altogether; if you keep them (I'd suggest replacing them with 105 63V 1050 electrolytic or somewhat lower capacitance - e.g. 3.35 - film types), do not remove 100k resistors R41 and R42 as these avoid getting an undefined potential (and thus possibly arcing due to overvoltage inside the caps) if the amplifier connected also uses coupling caps on its inputs (which, as it happens, is the case for the headphone amp that I use with my KT-80). The most critical coupling caps IMO are C49 and C50 near the MPX filter, which are only 3.35 but should be 105 or better 225 (225 63V 1050 types should still fit I think) for optimum performance. (Again, film caps could be a bit smaller, 4.75 would do.) The small brownish electrolytics around the MPX are low-loss types from ELNA, where many of the 'lytics and the PCBs seem to be sourced from. If they are replaced, use film types of the same value. (European manufacturers like Grundig used these, but I guess in Japan they were too expensive and locally available good electrolytics were employed instead.)"

Kenwood KT-313 (1979, $180)
Kenwood KT-413 (1979, $250)
The KT-313 and KT-413 are low-end tuners that are not recommended because superior tuners like the KT-615 and KT-7300 are so inexpensive. The KT-413 has 3 gangs and its selectivity, unmodified, is not sufficient for DXing. We're told that its unusual "motorized tuning" works well but may make it difficult to tune in a weak station next to a stronger one. The KT-313 and KT-413 usually sell for $10-20 on eBay, but one KT-413 sold for 70 cents in 12/03 and another went for $75 in 3/07. See our Kenwood brochures page for more about the KT-313 and KT-413.

KENWOOD KT-313 TUNER
$125.00 eBay

Kenwood KT-500
The KT-500 is a scarce little cheapie that is apparently the baby brother of the KT-800, KT-900 and KT-1000, and it's another example of why "rare" does not necessarily equal "good." The KT-500 usually sells for $10-25 on eBay.

Kenwood 600T (1976, $650, front, back, back with amp, brochure, block diagram, detector/MPX scheme: pulse count detector, charge injection cancellation discrete MPX switches, MPX PLL generated 38k with HA1156 chip)
The FM-only 600T was Kenwood's first tuner to use their pulse count detector circuitry, which was designed to reduce noise, and the 600T is a very quiet tuner. It has an 8-gang variable capacitor (it appears to have 9 gangs but 2 of the gangs are tied together - it uses a 2-gang variable capacitor for a local oscillator, unlike conventional local oscillators which use a single type variable capacitor), and uses 2 parallel IF filter paths (wide/normal and narrow). Wide mode uses linear phase LC filters, while narrow mode uses a 12-element ceramic filter section (three 4-pin filters with 4 elements, or stages, each). The 600T is among the most sensitive tuners but in stock form its adjacent channel selectivity is not as good as one might expect. It has excellent sound, in part because of the wide bandwidth, but will probably disappoint a DXer unless some of its filters are replaced with narrow ones. The catch there is that it uses the old-style 4-pin filters in narrow mode, rather than the 3-pin type currently available, so the filter mod is not a straight swap. See the DIY Mods page for information on adjusting the filters in the 600T. In addition to the IF bandwidth switch, the 600T's front-panel features include a button to switch the combination multipath/deviation meter, FM MPX filter switch, variable output knob, two levels of muting (or muting off), de-emphasis normal/25uS and dimmer on/off. On the back panel are fixed and variable RCA outputs, jacks for an oscilloscope and an AC convenience outlet.

Our contributor Charles has a 600T story: "In my kitchen, I took the McIntosh MR 78 down and put up the 600T so I could adjust my antenna better. The 600T has a marvelous signal strength meter calibrated in 10 dB increments. It's almost worth owning this tuner (or sibling KT-917) just for the useful strength meter. The strength meters on most tuners are useless, except perhaps for tuning. I still haven't done as much antenna experimentation as I'd like, but I'm beginning to like the 600T's sound so much I haven't put the MR-78 back. To get the full benefit of the 600T, you have to use the fixed output, which avoids an extra output buffer stage. On the MR 78, the level control is simply a low-impedance pot, like a passive preamp, so it doesn't much matter. As far as DXing, unfortunately the stock 600T is abysmal, with its "wide, wider, widest" IF bandwith control." The 600T's front panel resembles the KT-917's, leading some people to assume erroneously that the differences between the tuners are merely cosmetic, but the 600T is smaller and has very different circuitry inside. See the 600T vs. KT-917 page for Bob's technical comparison of the 600T to the KT-917, the results of a head-to-head shootout between the two tuners, and a quick comparison between the 600T and the KT-8300. The 600T usually sells for $450-500 on eBay, with a recent high of $611 in 6/09 and a semi-recent high of $728 in 5/06. A 600T with audiophile and DX mods, as well as manuals, sold for $1,325 on eBay in 5/06.

Kenwood KT-615 (1979, $300)
The KT-615 has 4 gangs and 4 filters and uses Kenwood's pulse count detector circuitry. It has an FM MPX filter and wide/narrow bandwidth switch, but its FM mode (auto/mono) and muting controls are on the same switch, meaning that one cannot choose to listen to a weak station in stereo. Stock, it's a pretty good tuner, but when modified with narrow filters, it makes a huge jump up the rankings and becomes an excellent tuner for DXing. The KT-615 also has a good AM section and can be a nice bargain for as little as $25 or less on eBay (and one sold for $1.00 in 1/08). Make sure the tip of the power switch is not broken, a very common problem with the KT-615 and KT-815. On rare occasions nice KT-615s (particularly with the rare rack handles) can go for $100 or more ($113 in 9/08). In the "ancient history" department, a perfect KT-615 modified with narrow filters sold for a stunning $256 in early 2001, before TIC and our FMtuners group helped make mods commonplace. See the DIY Mods page for information on DIY audio section mods for the KT-615. See our Kenwood brochures page for more about the KT-615.

Kenwood 650T
This excruciatingly rare tuner is identical to the 600T electronically, but has a bronze face. 650Ts on eBay sold for $851 in 9/05, $585 in 4/07 and $315 in 1/08.

Kenwood 700T (1975, $750, detector/MPX scheme: ratio detector, diode bridge MPX, PLL generated 38k with upc33C chip)
The 700T, which predated the 600T, is a very rare 5-gang tuner whose tuning dial resembles the KR-6600/9600 receivers. According to our contributor Charles, the 700T is the only Kenwood tuner that uses an analog dial to set a digitally controlled oscillator - a very unusual system that is also used in the Pioneer F-28. We don't have much info from users of the 700T, but here are an interesting S/N test sheet and the left half and right half of the 700T schematic, thanks to our contributor Lonnie. The 700T usually shows up only once a year or so on eBay, but three of 'em sold for between $400 and $450 in 4-6/09. The recent low was $305 in 4/07 and the all-time highs were $810 in 8/03 and $720 in 4/06. Be careful: a "very unusual" tuner is not the same as a "great" one.

Kenwood KT-800 (1981, $275)
The FM-AM KT-800 is the baby brother of the KT-1000 and KT-900 in the "Audio Purist" line. Only two inches high, it has digital tuning in .2 MHz steps, 8 memory presets, and a clock that can be displayed instead of the frequency. Signal strength is shown by an LED indicator with up to four bars. Except for the preset buttons, all of the controls (even the power switch) are hidden behind a door that pops out of the front panel. With the electronic equivalent of 4 gangs and good stock selectivity, the KT-800 is not a bad buy at its usual price of $30 or less on eBay, and one even sold for $1.00 in 7/08.

Kenwood KT-815 (1979, $440, front, inside, schematic)
The KT-815 has 5 gangs and 4 filters, with the main differences from the KT-615 being the extra gang and an output level knob on the 815's front panel. It also uses Kenwood's pulse count detector circuitry. In our panelist Eric's side-by-side test, a KT-815 with narrower filters installed was the equal of the McIntosh MR 78 and MR 80 for sensitivity and selectivity, although the Macs sounded a bit better. The KT-815 seems to be better for DXing than the KT-7500, but the 815 sometimes sounds a bit "thin" to audiophiles. In their own side-by-side shootout, our contributors Tim and Ann found the KT-815 to be very "electronic, harsh and two-dimensional" sounding compared to a Pioneer F-91. A contributor to our FMtuners group, however, posted this nice review that may illustrate the tremendous variability in different examples of 25-to-30-year-old electronics: "I think the KT-815 is a very attractive tuner and its layout is practical and uncluttered. Internally, the circuit layout is again attractive and uncluttered. The 5-gang FM front end employs dual-gate MOS-FETs as active amplifiers. There is a Touch-Action Servo Lock Tuner that works very well (grabs a station and holds it, but is defeatable). Wide and Narrow IF bandwidth selection. Double Conversion which is found only in professional grade equipment which results in dramatic improvement in signal-to-noise ratio when used with the pulse count detector. Pulse count detector ignores distortion by turning each FM wave into a precise and uniform pulse of energy. Pilot Carrier Cancellation subtracts the pilot signal from the audio output signal at no sacrifice to overall frequency response. Direct Coupled Operational Amplifier that is powered by a +- dual power supply. It ensures low distortion, wide dynamic range, and low output impedance, and will withstand 300% overload. Powerful, well-regulated power supply with 1,000 microfarad capacitors.

"Sonically, in my opinion, this tuner is a sleeper. It reminds me a lot of its more expensive brother the KT-917 (honestly). Being a audiophile rather than a DXer, I am more inclined to purchase based on sonics. This tuner, like the 917, has a 'big' sound and flat frequency response (which I prefer to the colored sound of some tuners). I would rather make the tonal adjustments via my control amp myself. The soundstage is large (not compressed) and spatial characteristics are excellent (even more so than the KT-917). I could easily discern individual instruments and their placement in the soundstage. The stereo separation is an incredible 55 dB and signal-to-noise ratio is an extremely quiet 80 dB in stereo. This tuner really does live up to these specs. I at no time felt any listening fatigue - in fact, I find myself listening to it more often and, depending on the station and its music source, I sometimes forget that I have the tuner on and not the CD player! This is no exaggeration. This tuner is currently used with a simple dipole antenna in a hilly rural setting. I pick up a classical station that is more than 50 miles away with a strong multipath-free signal. The result is outstanding sound quality and a very quiet background in the wide mode. I had occasion to use the narrow mode for a jazz station with a weaker signal, and it eliminated much of the interference with an almost imperceptible change in the frequency response. Other tuners I've owned have included well-cared-for 'like new' versions of the Pioneer TX-9100 and TX-9500, Kenwood KT-917, McIntosh MR 77 and MR 74, Yamaha T-2, and Fisher KM-60 and FM-100B, and I must say that dollar for dollar, the Kenwood KT-815 is the best value of them all." The KT-815 usually sells for $65-125 on eBay, with a record high of $276 in 9/04 for a "new in box" one and recent highs of $170-180. A KT-815 with TIC's DIY mods went for $218 in 8/07. KT-815s with rack handles are seldom seen. See the DIY Mods page for information on DIY audio section mods for the KT-815. See how one stock KT-815 sounded in comparison to other top tuners on our Shootouts page, and read our panelist David "A"'s Ricochet. See our Kenwood brochures page for more about the KT-815.

Kenwood KT-880 (1985, $235)
The KT-880D may be a sleeper but we wouldn't bother with the KT-880, without the D at the end. The KT-880 sells for $10-30 on eBay with a low of $1.50 in 4/05.

Kenwood KT-880D (1987, $269)
The KT-990D's much more common little brother, the KT-880D is also a decent and mostly unknown tuner. It has 4 gangs and wide and narrow IF bandwidths, and our panelist Bob likes it for reception capability and sound. Bob adds, "It appears that the KT-880D was very similar to the KT-5020, which followed it. While not exactly the same, they share some design traits like the same MPX chip, same RF front end, same buffering and lowpass filter after the detector (which I think is sonically important), and similar, if not the same, IF section. Differences are the KT-5020's PLL detector (the KT-880D uses a simple quad detector), and the KT-5020 has a buffer after the MPX that the KT-880D lacks. Is the KT-880D an overall overachiever? We'll let others decide for sure. My vote is yes." Our contributor Stephan compared his KT-880D to an Onkyo T-4500: "For tougher (more crowded) receiving conditions, I'd prefer the T-4500, since it features one more gang, one more IF filter and a nifty channel separation correction circuit for narrow IF mode (simple but effective; look out for Q202)." Stephan also speculated, "Maybe the usual cap mods and the like would be worth a try with the 880D. On strong signals, the Kenwood with its nominally lower distortion LA1235 (instead of the LA1266 as used in the T-4500) may sound better, though that's probably more a matter of alignment." But Bob does not quite agree: "The IF chips are wholly dependent on the type and quality of quad detector *transformers* attached directly to them, and how well they are adjusted. The difference of .015% vs .03% distortion is meaningless, as the filters, quad TX and of course, alignment, will be much greater factors." Our contributor Brian Beezley calls the KT-880D "one of the most sensitive tuners I've ever measured" in the detailed review on his website. The KT-880D usually sells for $35-75 on eBay, with a recent low of $20 in 4/07 and an all-time high of $92 in 1/09.

Kenwood KT-900 (1981, $350)
Part of Kenwood's "Audio Purist" series, this little brother of the KT-1000 uses their pulse count detector circuitry also found in the 600T and KT-615/815/917 series. The KT-900 has analog tuning but has a digital LED frequency readout in addition to the analog dial. It has 4 gangs (although we have an Audio Purist brochure that erroneously claims 5 gangs!) and 4 filters and, when modified, is similar in DX performance to a modified KT-615 or 815. The KT-900 usually sells for $20-50 on eBay, with a recent low of $11.49 in 7/06 and a high of $122 in 2/05. A KT-900 with matching KA-800 amp sold for just $64 in 5/04.

Kenwood KT-917 (1979, $1,000, detector/MPX scheme: pulse count detector, discrete CMOS switch driven with slimed pulses (no charge injection cancellation) generated by analog means, MPX PLL generated 38k with HA11223 chip)
The FM-only KT-917 was the successor to the 600T as Kenwood's flagship tuner. The KT-917's front panel controls are identical to those of the 600T, leading some internet commentators to assume erroneously that the differences between the tuners are merely cosmetic, but the KT-917 is larger and has very different circuitry inside. The KT-917 has a huge 9-gang tuning capacitor, similar to the 600T's 8-gangs-and-a-jumper capacitor, and the 917 also uses Kenwood's pulse count detector circuitry, but the similarity ends there. Unlike the 600T which uses two parallel filter paths (wide/normal and narrow), the KT-917 uses a single serial IF filter circuit with taps for the three filter bandwidths. It starts with a single ultra wide ceramic filter (there are two other ceramic filters but they're used only for meters and are not in the IF path), followed by a single tuned LC filter in wide mode, followed in narrow mode by four Murata "Surface Acoustic Filters" (sometimes called SAW filters, for Surface Acoustic Wave) which were specially designed by Kenwood and are also used in the L-07T II. As each filter is normally two elements, or stages, this would give the KT-917 a 12-element narrow mode, similar to the 600T. (There are two SAW filters in the wide IF bandwidth mode.)

Our contributor David Rich observes that like the McIntosh MR 78, which is "double-tuned at the input, then has a cascoded (better linearity) RF stage followed by another double-tuned filter, the KT-917 is the same except the drain - source connection of the cascode is double-tuned and the output of the cascode amp is triple-tuned. The oscillator gets an extra tuned stage to reduce phase noise and improve matching. The mixer is passive to keep the good IP3 [third-order intermodulation - Editor] rejection. The KT-917's Stereo MPX circuit is a zero-order sample-and-hold. A small pulse generated by an analog circuit turns on the MOSFET switch for a very short period of time. At that time the output follows the composite. For the rest of the time the output stays stable. This is not a switching system where the polarity of the composite is switched on 50% of the time (the older Kenwoods do that). The zero-order sample-and-hold can be done with diode networks alone and it shows up in even early tuners such as the Marantz 10B I think. It is all explained in the KT-917's manual. IC 9 is the switch (TC4066), C35 and C38 are the hold caps, and the opamp after that is a TL 072 (IC 10). It has to be a FET op-amp to hold the charge on the cap. IC1, IC5 and IC 12 are also upgrade candidates as are all the passive in the signal path except C35 and C38 which I would not touch. IC 10 needs high slew rate and fast settling time like all op-amps in a sample-and-hold application. See Linear Tech for an upgrade of the TC 4066 (this is a high risk move but may offer lower charge injection. It should only be done if you really understand the circuit and how a part change in the switch could really kill its operation. Remember that Kenwood dumped the timing circuit to the switch in the next generation tuner. The last Kenwoods used analog multipliers."

Our contributor Georges tells us that the KT-917 has "two RF amplifier transistors Q1 and Q2 (Q2 being a common gate amplifier) before the diode doubly balanced mixer." And the KT-917's service manual says, "The RF amplifier section has a wide-gap, 9-gang variable capacitor for the double-double-triple tuning system (one tuning stage for ANT, and two tuning stages for RF). The CC3588DE used as Q1 is a DD-MOS FET (selected SD-306) which features low noise and superior square response over a broad input level/frequency range. It also features a high power gain. VR1 adjusts Q1's input response to its maximum linearity. For servicing adjust VR1 so that the maximum deflection of the S-meter can be obtained. In the second stage, another double-tuning circuit is coupled to a common-gate amplifier, which features a lower input impedance and stable amplification with no influence from feedback admittance."

The KT-917 is extremely sensitive but anyone expecting state-of-the-art selectivity will be disappointed. The KT-917 is considerably scarcer than the 600T and can sell for $475-700 or more on eBay, depending on condition (one with rack handles sold for $980 in 3/07, and one without handles went for $830 in 3/09). See Bob's 600T vs. KT-917 page for a further technical comparison of the KT-917 to the 600T and the results of a head-to-head shootout between the two tuners, and the DIY Mods page for information on DIY audio section mods for the KT-917 and how to adjust its filters. See how one KT-917 sounded in comparison to other top tuners on our Shootouts page, and read our panelist David "A"'s Ricochet. See our Kenwood brochures page for more about the KT-917. [BF][EF]

Kenwood KT-990D (1988, $375, detector/MPX scheme: PLL detector, "Direct Pure" linear multiplying circuit with MC 1495L)
Somewhat of a sleeper until Jim's Shootout hit the presses, the fairly common KT-990D is a humdrum-looking black digital tuner. It has the electronic equivalent of 5 gangs, but 2 are in the local oscillator, so it's really like 4 by our traditional method of counting. The KT-990D has 2 ceramic filters plus an LC filter for the Wide IF bandwidth mode, and 3 ceramics in Narrow. The output amp is an NJM4560. There is a Direct Loop Linear Detector (DLLD), which is Kenwood's implementation of a phase locked loop detector, only seen on top performance tuner models. The "Distortion Cancellation Circuit" appears to generate a distortion-canceling signal that is mixed into the signal to correct for IF filter non-linearities. Our contributor John L. reports, "The KT-990D has a button labeled RF Selector that switches between Direct and Distance, which is the same as local/distant. There is also a button labeled Active Reception that switches between letting the user manually select the IF and RF settings or letting the tuner automatically select those settings." The KT-990D's current eBay price range seems to be $125-225, with a recent low of $102 in 5/09 and a recent high of $273 in 1/09. A KT-990SD, whatever that is, sold for $142 in 1/07 (please post in our FMtuners group if you know anything about the KT-990SD).

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Pioneer TX-9100 and TX-9500,
Kenwood KT-917,
McIntosh MR 77 and MR 74,
Yamaha T-2,
Fisher KM-60 and FM-100B
Kenwood KT-815 is the best value of them all

KT-880D was very similar to the KT-5020
Differences are the KT-5020's PLL detector (the KT-880D uses a simple quad detector)