UL - triode switch

torrence · 7th July 2008, 06:46 AM

A lot of SE pentode amps have a switch to change from triode to ultralinear taps on the output transformer. In principle, most switches can't handle the voltage from plate to ground which can often be around 450 V quiescent, plus the AC swing which could easily give 700 V. Do people worry about this, or have bad experiences with terminal to ground shorts? I couldn't find real specs for the max. breakdown voltages for common AC line switches, but even 220 VAC switches wouldn't need to handle more than about 300V max. Are there common switches designed for this that won't cost a load of money? I don't really want to get a lethal shock off my UL-anode toggle switch.

Eric

vitalstates · 7th July 2008, 07:18 AM

many use a relay driven by heater voltage.

Tweeker · 7th July 2008, 09:58 AM

An inductive DC load is about the worst case scenario for a switch (does not cross through 0 like AC, arcs stay lit easier). Most switches are rated for AC, not DC, or are rated lower for DC. The rating has more to do with the contacts and their breaking and making than the insulation. I would be wary of switching hot, do not do it if its break before make. Doing so may be hard not just on the switch, but the OPT.

Example of a relatively cheap 480VAC switch. Break before make.

7th July 2008, 06:46 AM	#1
torrence diyAudio Member Join Date: Feb 2008 Location: Oregon	UL - triode switch A lot of SE pentode amps have a switch to change from triode to ultralinear taps on the output transformer. In principle, most switches can't handle the voltage from plate to ground which can often be around 450 V quiescent, plus the AC swing which could easily give 700 V. Do people worry about this, or have bad experiences with terminal to ground shorts? I couldn't find real specs for the max. breakdown voltages for common AC line switches, but even 220 VAC switches wouldn't need to handle more than about 300V max. Are there common switches designed for this that won't cost a load of money? I don't really want to get a lethal shock off my UL-anode toggle switch. Eric

7th July 2008, 09:58 AM	#3
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	An inductive DC load is about the worst case scenario for a switch (does not cross through 0 like AC, arcs stay lit easier). Most switches are rated for AC, not DC, or are rated lower for DC. The rating has more to do with the contacts and their breaking and making than the insulation. I would be wary of switching hot, do not do it if its break before make. Doing so may be hard not just on the switch, but the OPT. Example of a relatively cheap 480VAC switch. Break before make. __________________ Be sure your foil hat has a good low impedance ground.

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7th July 2008, 07:18 AM	#2
vitalstates diyAudio Member Join Date: Jan 2006 Location: uk	many use a relay driven by heater voltage.

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