Re: Valve question
Juke box amplifiers usually leave the heaters on and only apply HT when a record is selected. The HT is supplied via a directly heated rectifier so it comes up quickly so by the time the mechanism is ready to play the record the HT is up to its working voltage.
Some amplifiers run the heaters at around half the normal voltage with no HT applied. When a record is selected a winding on the HT transformer applies the other half of the heater volts (assuming the winding is phased correctly) and the HT via the directly heated rectifier.
With the expected usage of a juke box I doubt if the valves ever suffered from cathode poisoning!
Keith
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