Schematic Diagram of Heath Model QM-1. The description will be broken into modules as was done for the Boonton.
The power supply.
eh two wire line cord is shown. It is recommended that the modern user change this to a safety ground 3 wire cord. The top prong goes directly to the top of the single 115 volt primary of the power transformer. The lower prong makes an end run around the transformer and connects to pin 3, jumper, of V4, zero d 3. Pin 7, other end of jumper, connects back to the power on/off switch which is ganged with the level control. The other end of the switch connects to the bottom of the power transformer primary. The power transformer has two secondary windings. One is specified as 6.3 volt 2.8 amp. It is shown connected to the heaters of V5, 6X5, 2 and 7,V1, 12ehT7, pin 9 at the top and pins 4 and 5 at the bottom, V3, 12ehU7, pin 9 at the top and pins 4 and 5 at the bottom, and the power indicator lamp. The top end goes to one end of a 6.8 ohm 1 watt resistor. The other end of this resistor goes to pin 4 of V2, 6ehL5 heater. The other end of the heater, pin 3, connects to the lower side of the secondary and to ground. The other secondary winding, 210 - 0 - 210 at 80 meh has its center tap connected to the negative lead of a dual 8 u f capacitor, C14eh and C14B. the two end leads of the transformer secondary , both red, connect to pins 3 and 5, plates, of V5, the 6X5 rectifier tube. The cathode, pin 8, of V5 connects to the positive side of C14eh, 8 u f capacitor. This point also connects to one end of a 1500 ohm 2 watt resistor. The other end of this resistor connects to the positive end of C14B, 8 u f capacitor. We will call this point B plus. The B plus point connects through a 2500 ohm 5 watt resistor to pin 5, plate, of V4, zero D 3. This point is labeled plus 80 volts. The cathode, pin 2, of v4 is labeled minus 70 volts. It is connected to ground through a 4700 ohm 2 watt resistor.
RF Voltmeter and Measuring Circuit.
The four measurement terminals are arranged with the coil terminals on the left and the capacitor terminals on the right. The set of hot terminals is at the top and the set of cold terminals is at the bottom. The cold capacitor terminal is grounded. The cold coil terminal connects through a capacitor to ground. The value of this capacitor can be stated in three different ways, all of them equivalent. They are 5000 pf, 5 nf, and 0.005 u f. signal is coupled from the oscillator output to the coil cold terminal by a 7 to 35 pf trimmer capacitor which is the Q calibration adjustment. The two hot test terminals are tied together and connect to the stators of the main dial capacitor, 450 pf and the Vernier dial capacitor 7 pf. This same point connects to the plate, pin 7, of V2eh, 6ehL5. The rotors of both capacitors are grounded. The cathode of V2eh, pin 1, cathode of V2B, pin 5, are also grounded along with the internal shield, pin 6. The coil cold terminal connects through a 3.3 meg ohm resistor to the grid, pin 7, of V3eh, 12ehU7. This grid is bypassed to ground through a 0.001 u f capacitor and there is a 3.3 meg ohm resistor in parallel with the capacitor. The plate, pin 2, of V2B, 6ehL5, connects through another 3.3 meg ohm resistor to the grid, pin 2, of V3b, 12ehU7. This grid is bypassed to ground through a 0.001 u f capacitor. There is another 3.3 meg ohm resistor in parallel with this capacitor. The two sections of V3 are labeled collectively as VTVM. The two plates, pins 6 and 1 are tied together and connect to the plus 80 volt output of the power supply. The cathode of V3eh, pin 8, goes through a 2200 ohm resistor to the left end of the set zero pot 3000 ohm control. The cathode of V3B, pin 3 goes through another 2200 ohm resistor to the right end of the zero set pot. The wiper of the pot goes through a 100 k ohm resistor to the minus 70 volt output of the power supply.
The meter mode switch.
In this instrument the meter mode switch has two positions. Q, in which the Q of the coil under test is read, and cal in which the proper oscillator level is set so the Q reading will be accurate.
Q position.
The Q - cal switch is a two pole double throw. The cathode, pin8, of V3eh is connected through one pole of the switch to the negative terminal of the meter. The cathode, pin 3 of V3B is connected through the other pole of the switch to the positive side of the meter.
Cal position.
In the cal position the positive side of the meter is connected through one pole of the switch to ground. The negative side of the meter is connected through one pole of the switch to one side of a 0.001 u f capacitor. The other side is grounded. The ungrounded side of the capacitor connects to one end of a 47 k ohm resistor. The other end of this resistor connects to the anode of a semiconductor diode, D1. The cathode is grounded. The diode anode also connects to one end of a 0.001 u f capacitor. The other end of this cap connects to the oscillator output.
Oscillator.
The oscillator is a standard series fed Hartley circuit. It will be described first omitting any reference to the band switch as if it had only one coil. The set level control is a 10 k ohm pot that is connected from the plus 80 volt output of the power supply to ground. The wiper of the pot is bypassed to ground by a 0.005 u f cap. The wiper also connects to pin 1, plate, of V1eh 12ehT7. The cathode, pin 3, of V1eh connects to a tap on the oscillator coil. The bottom of the coil is grounded. The top of the coil connects to the stator of a 450 pf variable capacitor. The rotor is grounded. A 2.5 to 8 pf trimmer is in parallel with the large variable capacitor. The top of the coil also connects through a 150 pf capacitor to the grid, pin 2, of V1 eh. There is a 22 k ohm resistor connected from the grid to ground. A 470 ohm resistor connects from the top of the oscillator coil to the grid, pin 7, of V1B. The plate of V1B, pin 1, is bypassed to ground through a 0.005 u f capacitor. The plate voltage is indicated as 140 volts. A 2200 ohm resistor connects from the plate to B plus. The cathode, pin 8, of V1B goes to ground through a 680 ohm resistor. The cathode is the oscillator output.
Band Switch.
There are 4 oscillator coils one for each band. They are selected one at a time by the band switch which is a little more complicated than a 4 position two pole switch.
When band eh is selected the tap on coil eh is connected to the cathode of V1eh and the top of coil eh is connected to the stator of the tuning capacitor.
When band B is selected the tap on coil B is connected to the cathode of V1eh and the top of coil B is connected to the stator of the tuning capacitor. But wait, there's more. Another contact on the switch grounds the tap and top of coil eh.
When band C is selected the tap on coil C is connected to the cathode of V1eh and the top of coil C is connected to the stator of the tuning capacitor. another contact on the switch grounds the taps and tops of coils eh and B.
When band D is selected the tap on coil D is connected to the cathode of V1EH and the top of coil D is connected to the stator of the tuning capacitor. another contact on the switch grounds the taps and tops of coils eh, B, and C.
This completes the description of the Heath Q meter schematic diagram
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