Can the Sony TCM-280 be hi speed and hearing aid electron tube equipped?

Your risk. This is not expert advice.


The excellent looking TCM-280 has not be tried yet. It may actually not need a higher speed.


By looking at a small towel sized scanned and enlarged schematic from the service manual...


The motor SM-203 is driven by a servo board. The motor has 6 terminal connections and 1 ground.


At the block diagram of the TCM-280 or TCM280B (for black color) the motor blog diagram has inside it an LED apparently sending light to a phototransistor. Is this used as feedback signal of rotation?


The servo board consists of an IC. Pin 3 of this IC is connected to the LED. The other side of the LED is connected to B+, motor winding supply and phototransistor collector.


Speed adjustment is done by a external DC amp feeding the servo board IC. Variable resistors for speed adjustment are connected to this DC amp. It should not at all an easy task to increase speed for 7ips by just increasing the power supply. All LEDs including the power on LED, transistors (unless they can operate at higher potential without must bias modification etc) and control circuits must be protected. Would a series resistor protect LEDs?


Anyway.


All main analog amplification is done by a dedicated IC, Sony CX807.


It has a record amplifier. Input is pin 4.


Playback amplifier. Input pin 2.


Output of both amps is pin 24. The PB equalizer is connected externally consisting of RC feeding back to pin 1.


Inside the IC also there is a line amp with AGC (automatic gain control) possibility. Output of line amp is pin 19. The signal goes to a tap of an inductor. One side of L goes to ground. The other side is the signal continuing its route to an R in parallel with C which feeds the recording head. This is possibly for constant current music signal feeding and some extra high frequency boost by the capacitor.


There is another IC on another board for end of tape detection.


There is a nice discrete transistor with output tapped transformer etc for providing the AC bias. A typical oscillator. Bias amplitude can be changed by either connecting the 33 ohm resistor or the 69 ohm resistor.


The music speech switch apparently turns on or off the compressor. It is connected to the pin 5 of the CX807 IC which controls AGC drive inside the IC.


Mic sensitivity can also be changed internally apparently at some part of the analog board.


Would it be also possible to make an electron tube board with 3 to 4 hearing aid type subminiature electron tubes?