Pure Oil Corp. 508 Schematic

Pure Oil Corp. 508

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Product Information:
Model:508
Manufacturer:Pure Oil Corp.

Schematics Content

Page 1:

Be sure R.F. and I.F. stages are accurately aligned before measuring gain. R.F. gains can be measured with a "channel" type instrument containing a tuned and calibrated R.F, amplifier. A vacuum tube voltmeter may be used for audio gain measurements. Observe following precautions:

1. For all gain measurements connect signal generator as shown. Use 600 KC. signal with 400 cycle modulation (use nearby frequency if local station interferes.)

2. For R.F. and LF. measurements connect negative terminal of a 3 volt battery (two 14 volt cells in series) to A.V.C. lead and positive terminal to chassis. This provides a definite operating point.
IMPORTANT: Disconnect battery when measuring audio stage gains.

3. Be sure radio is carefully tuned to generator signal (use weak signal for sharp tuning.)

4. When using "channel" type instrument carefully tune it for maximum output at desired frequency before making measurements.

The R.F. and I.F. stage gains shown below are less than under normal operating conditions due to the use of 3 volts fixed bias in order to establish a definite operating point. Therefore, these values are not intended to indicate the full capability of a stage.

Differences in tube characteristics, tolerance of parts, adjustment of tuned circuits, and variations of line voltage will influence stage gain. Accuracy of measurements is dependent upon careful tuning of receiver to generator signal and experience in using your test equipment. These factors may create considerable variation in gain measurements.

AUDIO OSCILLATION
The audio system of this receiver utilizes a two stage type of inverse feed-back arrangement and should it ever be necessary to replace the speaker or output transformer it is important to maintain a definite phase relationship in the feedback circuit. If the connections to the output transformer are reversed or if the feed-back connection is made to the wrong side of the output transformer secondary, the system will become regenerative instead of degenerative. Under those conditions audio oscillation may result. If that occurs, oscil. lation may be prevented by reversing the connections to the primary of the output transformer.

Page 2:

SOCKET VOLTAGES
Measured with voltmeter having sensitivity of 1000 ohms per volt except where indicated by (*).

VOLUME ON FULL WITH NO SIGNAL RANGE SWITCH IN BROADCAST POSITION DIAL TUNED TO 540 KG, MANUAL BUTTON PUSHED IN

Dial And Pointer Drive Cord Arrangement

IMPORTANCE OF MAINTAINING FIXED POSITIONS FOR LEADS AT TOP OF CHASSIS

The wires shown in the above illustration are associated with tuned circuits which carry radio frequency currents. Therefore, care must be exercised to insure that they are properly rested and spaced. Anchoring and fixing spacing of wires minimizes freedom of movement and is utilized to maintain a stable arrangement.

Since the relative positions of these wires may affect tuned circuits it is important to avoid any change in arrangement after the receiver has been aligned. If the position of the wires has been disturbed, it is advisable to re-check alignment (see previous page for alignment procedure).

Page 3:

Band-switch Shown at 1st Position

Broadcast Band 540-1725KC.

Band-switch shown at 2nd position clockwise

Foreign band 11.4-15.5MC.

band-switch shown at 3rd position clockwise 31M. band 5.9 - 10.0 MC.

Page 4:

1. The chassis and loop antenna should remain in their normal position in the cabinet throughout the following procedure.

2. Check arrangement of leads to push-button switch as shown in illustration on following page.

3. With the gang condenser fully meshed, dial pointer should be in the position indicated by the last division below 55 on the dial. If it is set incorrectly, release pointer clip on dial cord and reposition pointer.

4. Connect output meter across speaker voice coil.

5. Connect the ground lead of the signal generator to the receiver chassis.

6. Set volume control at maximum volume position and use a weak signal from the signal generator.

7. Push in the manual button and leave it in that position throughout the alignment procedure.

IMPORTANT: Align this receiver in exactly the order shown below. Broadcast band must be aligned before short wave bands.