Lighthouse Electric Tech Support

 

Stand-By Switch for the SAPS1 Power Supply

All solid-state power supplies, SAPS1 is one of them, produce plate (h.t.) voltage the instant the power is switched on. Cathode stripping occurs when the plate voltage is applied before the cathodes of the vacuum tubes are heated-up and can freely emit electrons. The relatively high voltage on the plate will RIP them from the cathode material. This is called "Cathode Stripping", because it "strips" the cathode of its electron-emitting materials, and will eventually destroy the tube.
Here comes the "Stand-By" switch to the rescue. This switch interrupts the plate current until the cathodes are heated-up, usually 15-30 seconds. On large power tubes it may take longer.


Fig.1 Example of a Stand-By switch circuit.

 

This switch is operated as follows: Before turning the main power switch on, make sure the "Stand-By" switch is off. Now the main power switch can be turned on. After the tubes had enough time to warm-up, the stand-by switch can be turned-on. The amplifier is in operation.
At the end of the session, the stand-by switch should be switched off first, then the main power switch. A simple ON-Delay timer circuit could be employed to do this task automatically.

Since the SAPS1 may not be operated without a load, a load resistor (27k-47k 5-7Watt) must be connected to its h.t. output during the stand-by period. It is advised to install this resistor suspended on a separate terminal strip.


Fig.2 Connecting a Stand-By switch to SAPS1. Neon indicator light is optional.

 

 

 

 

THESE PROJECTS ARE PROVIDED 'AS-IS', WITH NO WARRANTY OF ANY KIND.
USE OF THESE CIRCUITS SHALL BE ENTIRELY AT THE USER'S OWN RISK.

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