Standby switch

elementx · 23rd January 2006, 05:09 PM

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?

anatech · 23rd January 2006, 09:23 PM

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

cerrem · 23rd January 2006, 09:34 PM

Make sure that the screen voltage as well as the plate voltage are shut down on the output valves..

Chris

Giaime · 24th January 2006, 08:12 AM

Quote:

Originally posted by anatech

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

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

elementx · 24th January 2006, 01:08 PM

100ohm 10watt in parallel, is that how its done?

anatech · 24th January 2006, 02:16 PM

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

amperex · 24th January 2006, 03:46 PM

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.

23rd January 2006, 05:09 PM	#1
elementx diyAudio Member Join Date: Jul 2005 Location: cleveland, ohio	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?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
standby switch	9am53	Tubes / Valves	17	25th October 2010 12:24 PM
Where do you put the standby switch	duderduderini	Tubes / Valves	13	4th October 2008 04:39 PM
Standby Switch	dre7	Tubes / Valves	6	18th October 2007 08:07 AM
Standby switch for Quad II?	Zombie	Tubes / Valves	13	13th March 2003 11:20 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

23rd January 2006, 09:23 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

23rd January 2006, 09:34 PM	#3
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	Make sure that the screen voltage as well as the plate voltage are shut down on the output valves.. Chris

24th January 2006, 01:08 PM	#5
elementx diyAudio Member Join Date: Jul 2005 Location: cleveland, ohio	100ohm 10watt in parallel, is that how its done?

24th January 2006, 02:16 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

24th January 2006, 03:46 PM	#7
amperex diyAudio Member Join Date: Feb 2005 Location: MI	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.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)