2. amps-preamps
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Speaker Switch That Protects Tube Amplifier

A EE friend of mine and I are planning to build a switch box that will allow me to toggle between my Yaqin MC-30L tube amp and my Integra 50.1 receiver to power my speakers.

The current plan is a very basic setup that would require the tube amplifier to be shut down before switching so that it isn't left without a load.

The utopian goal would be to be able to switch between the two amplifiers with a single source feeding both (i.e. the Yaqin has an Apple Express for a source and the Integra has an Apple TV so both could be running from iTunes on my Mac) without risk of damage to the tube amplifier.

I'm assuming that this would be complicated at best and probably isn't worth it, but thought I should as before we purchase parts.
mceljo
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almarg
9,670 posts
 
VERY clever idea from Imhififan. Kudos!

To be sure it's clear, I would reword the description of the Deck 3 connections as follows:

Deck 3: pole connect to 8ohm 100w Dummy Load Resistor; other side of that resistor to Tube Amp - output; position A & B jumpered and connected to Tube Amp + output; position C open.

Also, if this approach is pursued it might be desirable to use something like a 16 ohm 50W resistor, or even a 32 ohm 25W resistor, rather than an 8 ohm 100W resistor. The reason being that when the switch is thrown between positions B and C there will be a brief instant when the tube amp will see the loading of both the speaker and the resistor. That may not be a problem anyway, but I can envision the possibility of a significant thump occurring with an 8 ohm resistor, especially if the amp uses feedback.

Also, Mceljo, as opposed to the approach you described earlier, with this approach you would of course have to provide markings or some other means of identifying which specific terminals each specific amp should be connected to.

Marty (Viridian), thanks for the nice words and the good wishes, which I reciprocate.

Best regards,
-- Al
mceljo OP
1,357 posts
 
This sounds like a great alternate solution that someone else may choose to use. I have some of the parts in hand and almost everything else is in the mail. The only missing piece is some 10awg cable from Blue Jeans Cable as the stuff that we got from Parts Express didn't turn out to be what we wanted.
mceljo OP
1,357 posts
 
The box of parts has been passed to the EE in case he gets time before we get time to overlap. Two dad's with small kids means very little free time and even less overlapping free time.
mceljo OP
1,357 posts
 
As I suspected, my buddy couldn't contain himself and I have the completed switch on my desk at work this morning. I should have time to install it tonight.

One of our design criteria was to only use components that don't require a break-in period. Also, all components have been room temperature heat treated for the best possible performance.
mceljo OP
1,357 posts
 

@therandyman - Here you go.

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