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Using GT tubes as substitutes for non-GT tubes
From "Radio News"
Warrn J. Dougherty11/44

Back      Warren J. Dougherty, a serviceman of Kinkaid, Kansas, has called to our attention one of the factors most overlooked when replacing G-type tubes with the more newly-designed GT tubes. Invariably these GT tubes, with metal base, have their No. 1 pin grounded. Inasmuch as many manufacturers use all available socket pins for common tie-points, considerable damage may be caused when grounding the No. 1 pin. A particular case is the RCA Model BT-42 which was originally equipped with G-type tubes. When changing to GT tubes with metal base, the condenser, C16, 400-µfd. condenser and 1-megohm resister, R7, in the plate circuit of the 1H5 should be disconnected from the No. 1 pin of the 1N5 tube socket, as in this particular case, it was used as a common terminal connector. The metal base occasionally will short out the plate voltage from the 1H5 tube, resulting in a nonoperating receiver.

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