AMPLIFIER TUBE LAYOUT

ALIGNMENT PROCEDURE Alignment Indicators:

A high resistance volt meter is necessary for measuring D.C. voltage during F.M. alignment. An output meter is also necessary to indicate minimum audio output during F.M. ratio detector alignment. The output meter may be connected across the speaker voice coil.

For A.M. alignment, the high resistance volt meter can be used as indicator by measuring developed A.V.C. voltage.

F.M. RATIO DETECTOR ALIGNMENT 1. Connect a 680 ohm resistor between pins 5 and 7 of the ratio detector tube 6AL5. Connect the D.C. probe of the indicating meter to the negative lead of the 5 mfd. electrolytic condenser. The common lead is connected to ground.
2. Set the generator at 10.7 m.c., modulated 30 % at 400 cycles (AM). Turn the volume control to maximum volume and connect the generator to the driver grid, pin l, of the 6AU6 in series with a 01 mfd. condenser.
3. Adjust driver transformer, T5, for maximum D.C. across the 5 mfd. electrolytic condenser.
4. Remove the meter leads and disconnect the 680 ohm resistor. Connect two 100,000 ohms (+ 1 %) resistors in series, across the 22,000 ohms ratio detector load resistor. Connect the common lead of the indicating meter to the center point of the 100,000 ohm resistors and the D.C. probe to terminal "A" of the ratio detector transformer, T6,
Repeat connections as in step 2 above and adjust 16, bottom core for zero D.C. balance. This point is approached rapidly and continued adjustment causes the indicated polarity to reverse. A slow approach to zero is an indication of severe detuning.
Adjust T6 top core for minimum audio output. Alternate the adjustments of the top and bottom core of T6 until minimum audio output and zero D.C. balance occur at the same point.
6. Disconnect the two 100,000 ohm resistors and repeat steps two and three, eliminating the 680 ohm resistor.

7. Repeat steps 5 and 6 until further adjustment does not improve the calibration.

A.M. ALIGNMENT 1. Connect the signal generator to pin l, converter grid, 6BE6 in series with. 01 condenser. Tune the generator to 455 kc.
2. Turn the radio dial to a quiet point at the low frequency end of the variable condenser. 3. Adjust the A.M. I.F. transformers for peak output.
Connect the signal generator to the antenna lead in series with 200 mmf. Tune the generator to 1400 kc.
5. Turn the radio dial to 1400 kc, and adjust the oscillator trimmer and the loop trimmer for peak output.
6. Set the generator and set at 600 kc. and " rock in " L7, oscillator coil.

Correct alignment of 455 kc. I.F. requires that the 10.7 mc. F.M. I.F. be aligned previously.

F.M. I.F.-R.F. ALIGNMENT 1. Connect the D.C. probe of the high resistance meter to the negative lead of the 5 mfd. electrolytic condenser and the common lead of the meter to ground.
2. Set the generator at 10.7 m.c., modulated 30 % at 400 cycles (AM). Set the radio dial at the low frequency end of the variable condenser and connect the signal generator in series with a. 01 condenser to pin ? of the 3. Adjust the I.F. transformers for peak output on the meter.
Set the generator at 106 m.c. and connect the high side in series with 120 ohm resistor and the low side in series with 120 ohm resistor to the F.M. antenna terminals. Set the radio dial at 106 mc.
5. Adjust the F.M. osc, ceramic trimmer and the F.M. antenna trimmer maximum output.
6. Set the generator and radio dial for 90 mc. and adjust L3 and L2 oscillator and antenna coil for peak output.

MODEL 8121 TUNER MEASUREMENTS, VOLTAGE AND RESISTANCE

MODEL 8121 AMPLIFIER MEASUREMENTS, VOLTAGE AND RESISTANCE

POWER OUTPUT Undistorted... in watts Maximum,. 14 watts CIRCUIT DESCRIPTION This receiver is a twelve tube combination FM - AM superheterodyne radio with provision for phono operation. Three separate sections are employed for the entire receiver; a tuner, Amplifier-power supply and a metal encased auditorium speaker.

The tuner incorporates two separate con vertors, one for FM and the other for the broad cast band. A range switch is provided with a third position allowing. phonograph operation through the sound channel. A 6U5 / 6G5 tuning sye tube facilitates visual indication of proper tuning for both AM and FM operation.

The set utilizes a ratio detector eliminating the necessity of a limiting stage preceeding the detector and having an inherent insensitivity to amplitude modulated signals.

A loop antenna is included for the broad cast band.

The amplifier section employs two 6J5 tubes as phase inverter and amplifier driving a pair of 6V6 in push-pull operation which deliver ten watts of undistorted output from a Rola G12 auditorium speaker.

A 504 rectifier is used in the power supply with separately filtered sections for both the tuner and amplifier.