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Originally Posted by regenfreak
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another series resistor to the IF out hot side, as required (value depending on IF transformer ratio; ~50-150 Ohm should do).
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No, 50-150 resistor would heavily load down the IF amp LC tank giving completely wrong response curve. Min value would be 100k to 330K plus HV DC isolation cap. Valve IF amp has very high I/O impedance. |
And again a correction is due: the narrow IF bandwidth, as mentioned, is good for inspection of distortions and spurs, but for gain and selectivity sweeps the opposite is true, i.e. the IF transformer bandwidth should be made considerably wider than the expected front bandwidth.