Pure Oil Corp. 508 Schematic

Pure Oil Corp. 508

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Manufacturer:Pure Oil Corp.

Schematics Content

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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.

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.