In TV sets with heater chains; some manufacturers put a rectifier across the on/off switch, pointing the opposite way to the HT rectifier. That tactic was defeated in later models because manufacturers found they could reduce the dropper resistors by half-wave rectifying the heater supply.A good compromise is to put the filaments at half power in a standby mode when the amp is not used.
That allows the amp to come on rapidly when full power is applied, but there is much less thermal shock to the filaments, which is likely what causes filaments to fail sooner.
Depending upon the design, using a DPST (or DPDT) switch to connect a power resistor of the appropriate value in series with the filament power, and also switch off the plate voltage, would do that.
Sometimes in RF/IF circuits, manufacturing tolerances cause slight variations in electrode capacitance that can take the tuning off trim.Somewhere I read that when you put in new tubes you have to tweak/adjust the circuits somehow and that this is something a professional should do. ?
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