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Yamaha T7 - tuner

 

 

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Tuner

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Yamaha

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Dal sito :  http://www.fmtunerinfo.com/yamaha.html

 

Yamaha T-7 (1980, $410, photo, closeup, schematic, IC data, owner's manual) search eBay
Don't confuse this tuner with the T-07, a cheap digital model listed above. The T-7 is a 4-gang, black analog tuner with motorized presets. Our contributor PZ reports: "The T-7's front panel layout is almost identical to the T-1's. They both have the same 5 push buttons on the left below the dial and meters on the right. The buttons are Calibration Tone, Hi-Blend, Muting/OTS (off/multipath), RX Mode (auto-DX/local), Function (AM/FM). There is no option for mono. Both tuners have a fixed level output and a variable output on the back panel. The attenuator of the variable output is a thumbwheel located on the bottom of the unit (front center). This is very nice for A/B comparison against another tuner because the level can be matched easily. The T-7 incorporated some 'digital features' at the end of the analog age. The tuning meter found on the T-1 is omitted, and in its place is a pair of horizontal green lines flanking the red vertical marker. The brightness of the green lines change as the red marker sweeps through a station. Equal brightness of the two lines indicates centering. The frequency scale is just white letters marked on the black finish below these indicators, very small and hard to read. The problem is lessened by having 5 small lighted presets buttons so that there is less manual tuning. A motor moves the tuning knob to get to the preset station. I have only seen this gimmick in one other analog tuner, the Nakamichi 430. It does work, gets to the right place every time. The analog signal strength meter on the T-1 is also replaced by a 24-segment 'signal quality' meter on the T-7. Pushing down the Muting/Multipath button softens the brightness of this meter and I think it becomes just a multipath indicator. The space made available by eliminating the tuning meter is filled by the Local/DX lights and the stereo light. As far as audio quality goes, I couldn't hear any significant difference between the T-7 and the T-1, and also no difference from the digital TX-1000U." See PZ's introductory paragraphs at the top of this page for more info on the T-7. Our panelist Bob adds: "I just put a T-7 into working order with a total realignment. WOW is all I can say for the sound. Very low measured distortion, and very nice bass. A bit of a pain to tune, as the dial is small and not lit, but worth it. It has a crystal lock that works well. The T-7 is similar to the T-1 cosmetically, but I'm not sure about the circuitry. There appear to be some fancy circuits in the T-7 that have not been noted before, but I have no manual so can't say. Perhaps it is a pulse count detector or...? The T-7 reminds me of an econo Tandberg with linear dial and presets. It has a wide/narrow IF bandwidth switch (but they call it 'distant/local'), and decent specs."

Our contributor Brian B. did some work on his T-7: "The Yamaha T-7 is an interesting analog tuner with sophisticated circuitry and an intriguing motorized station memory system. It also has an unusual balun arrangement. The T-7 has a center-tapped antenna coil in its front-end module. In the usual arrangement the whole winding provides a 300-Ohm balanced input, while one side of the winding with respect to the grounded center tap provides 75 Ohms. However, this scheme works well only if the leads to the rear-panel terminals are short - a couple inches at most. Even if the balanced winding is connected to the rear panel with 300-Ohm ribbon cable, the impedance of one side with respect to ground isn't likely to be anywhere near 75 Ohms. I encountered this problem in a Technics ST-S16 tuner, whose 75-Ohm input was essentially unusable due to the awful return loss (terrible impedance match). The T-7's front end is far from the rear panel. Yamaha solved the connection problem by providing a second transformer near the antenna terminals. This transformer connects to the front end using a balanced wire pair. (Actually three wires are used, with the center wire not connected at either end. Presumably this arrangement provides an impedance closer to 300 Ohms for the spaced outer wires.) The rear transformer is resonated by capacitors on the primary and secondary windings. In my tuner this transformer was not well resonated in the FM band. In fact, bypassing this 'balun' improved the 50 dB quieting sensitivity by 1 dB at 98 MHz and 2 dB at the band edges. This is the largest improvement I've yet seen from a balun bypass. To bypass the rear transformer, unsolder the wire pair at the front-end terminals. You can leave the wires connected at the rear and secure the pair by wrapping them through nearby holes in the side panel. Next, snip the lead from the coaxial input socket to the board. Solder a short piece of RG-59 to the coax connector, grounding the shield directly at the connector. Run the coax around the board to the bottom side. Solder the center conductor to the rear antenna terminal, marked ANT1 on the top of the board. Scrape the green solder mask from the nearby groundplane and solder the shield there. It's important to run the coax to ANT1, not the other side of the input coil marked ANT2. The two sides of the input winding do not present the same impedance to ground, presumably because the coupling to the other winding differs. I have seen this effect in other tuners. In the T-7, sensitivity is better using ANT1." An owner's manual for the T-7 may be downloaded free from the Yamaha website. The T-7 can sell for as low as $50-60 on eBay but $100-130 is more likely. [BF]

 

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Manuale:  http://www.fmtunerinfo.com/T-7owners.pdf 

 

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