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