The table below provides connection data for Stancor Poly-Pedance modualtion transformers - model numbers, A-3898 (300 watts) and the A-3899 (600 watts). Under the column headed Primary P-to-P Impedance are listed the modulator plate loads most commonly used. The body of the table contains the possible Class C loads for these specific modulator plate loads. In the column adjoining the modulator plate loads are listed the proper terminals to use for these loads.
Finding Intermediate Values Not Found in the Table
Quite often it is desired to use an intermediate value of plate load not found in the table. For example, it is desired to match a pair if 6L6's with a 6600 Ohm plate load to a 10 kOhm Class C load. In the column headed Primary, 6000 Ohms is the closest plate load to 6600 Ohms. Therefore, when using the 6000 Ohm primary listing as a 6600 Ohm primary, a secondary listing of 6000/6600 or 0.909 times 10 kOhms (0.909 x 10,000) or 9100 Ohms should be used. The nearest listed secondary load is 9200 Ohms. This combination results in a mismatch of only one percent.
In making the primary connections, terminals listed under P are the plate terminals and those listed under B are the modulator plate voltage terminals. Secondary connections for Class C loads are made according to the instructions at the top of the column where the desired Class C load is found. If more Class C current must pass through the transformer than the series connection will carry, then a parallel connection must be used. A parallel coil connection will carry twice the current of the series connection.
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