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previous: Mark Owens I am building a single-ended little... -- 6/21/2000 1:02 PM View Thread

Re: Standby switch

6/21/2000 2:16 PM
MBSetzer
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Re: Standby switch
If it is like the Kalamazoo Model 1, you would probably not benefit that much using a standby as far as preserving tube life during amp turn-on.  
 
The 6X4 is a slow turn-on indirectly-heated-cathode rectifier, which allows ample time for the other tubes' heaters to warm up before it begins to pass the high voltage B+ in their direction. So your preamp & power tubes are already preserved at turn-on as well as they would be with a standby switch.  
 
OTOH, if you expect to often leave the amp idling as it *stands by* while you are taking a break, and prefer to be able to reduce the wear from accumulation of idling hours that are about equivalent to playing hours, you might want a traditional type standby that turns off the B+ while still leaving the heaters at full filament voltage.  
 
This switch is commonly installed in the B+ line between the first filter cap and the OPT, depending on the amp this might allow the B+ at the cap to rise a bit when the switch is open, make sure the first cap is rated high enough. Another location would be instead to switch the HV-secondary center-tap connection to ground, this is supposed to accomplish the same effect without putting as high a voltage across the switch, but this way the rectifier cathode has a full turn-on surge as it charges the first cap each time standby is used.  
 
Either way a major benefit of a standby is after a band break so you can go back to the amp and get instant music without having to wait for the amp to warm up every time. Leaving the heaters running through the breaks also reduces the number of times the heaters are turned on & off, and that has traditionally been one of the most common reasons for premature tube failure; burning out the heater due to its turn-on surge before the rest of the tube has even begun to show any wear.  
 
Hope this helps,  
Mike

 
Replies:
SteveG I put cathode stripping right up th... -- 6/21/2000 11:59 PM