standy switch
where do you install a standy switch on a tube amp to maintain a safe load while removing the output to the speaker?
Also, the princeton amp calls for 1/4" jacks that are closed when there is nothing inserted. is this required? or can i use a regular open 1/4" jack?
where do you install a standy switch on a tube amp to maintain a safe load while removing the output to the speaker?
Also, the princeton amp calls for 1/4" jacks that are closed when there is nothing inserted. is this required? or can i use a regular open 1/4" jack?
Hi elementx,
The standby switches I've seen interrupt the center tap of the secondary for the high voltage. I've seen the odd one turn the heater off of the rectifier tube (I don't like this).
The shorting jack prevents having an open transformer secondary. The short may blow the fuse, possibly damage the outputs. An open may cause the insulation in the output transformer to break down. It would also cause the tubes to possibly arc. Of the two, I choose the short.
Use the shorting jack.
-Chris
The standby switches I've seen interrupt the center tap of the secondary for the high voltage. I've seen the odd one turn the heater off of the rectifier tube (I don't like this).
The shorting jack prevents having an open transformer secondary. The short may blow the fuse, possibly damage the outputs. An open may cause the insulation in the output transformer to break down. It would also cause the tubes to possibly arc. Of the two, I choose the short.
Use the shorting jack.
-Chris
Make sure that the screen voltage as well as the plate voltage are shut down on the output valves..
Chris
Chris
anatech said:
Hi Chris,
Perhaps is better to use the most used solution, an open jack with paralleled a 100ohm 10W resistor 😉 you save both things with this 😀
Hi elementx,
I've seen that a couple times, just wire the resistor across the output jack. I don't know how effective this will be as the reflected impedance to the tubes is going to be extremely high. I suspect a shorting jack is the better solution.
-Chris
I've seen that a couple times, just wire the resistor across the output jack. I don't know how effective this will be as the reflected impedance to the tubes is going to be extremely high. I suspect a shorting jack is the better solution.
-Chris
Place a 20 ohm 25 watt resistor on the 1/4" speaker plug that is disconnected when a 1/4" jack is installed. 1/4" plugs are available with the normally closed contact. See Antique Electronic Supply in Tempe, Az.
As for a standby switch, interrupt the transformer B+ center tap. For best high voltage standoff, use a 240 VAC rated 10 to 15 amp switch & connect the transformer center tap wire to the switch contact that does not have the 'shortest insulated distance' to the toggle part in the interior of the switch. That would normally be the switch lug in the center of the switch body that is say less insulated to ground.
When the switch is in the on position, it connects the CT to ground & no potential above ground exists in the switch. If the switch has a metal (conductive) toggle, make sure it is grounded to the metal chassis. That would exclude plastic threaded switch shafts for mounting.
I am not trying to cause any fear here, just the best way to wire a quality switch. I never experienced a shock from a standby switch nor heard about any internal arcing issues. Obviously, a cheap 120 vac mini toggle switch is not what one would use in this circuit.
As for a standby switch, interrupt the transformer B+ center tap. For best high voltage standoff, use a 240 VAC rated 10 to 15 amp switch & connect the transformer center tap wire to the switch contact that does not have the 'shortest insulated distance' to the toggle part in the interior of the switch. That would normally be the switch lug in the center of the switch body that is say less insulated to ground.
When the switch is in the on position, it connects the CT to ground & no potential above ground exists in the switch. If the switch has a metal (conductive) toggle, make sure it is grounded to the metal chassis. That would exclude plastic threaded switch shafts for mounting.
I am not trying to cause any fear here, just the best way to wire a quality switch. I never experienced a shock from a standby switch nor heard about any internal arcing issues. Obviously, a cheap 120 vac mini toggle switch is not what one would use in this circuit.
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