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Speaker Switch with tube amps?


Emile

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Was wondering if there is a speaker switch that can be used with tube amps ... not even sure if it possible since the tube amps require an ohm load :( Any switch would temporarily disconnect.

But :D getting a new (old) pair of KP-3002's and wanted to try those with my Bob Latino VTA ST70 (without unplugging my Forte's).

Many thanks for any inputs!

Cheers, Emile

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Guest wdecho
On 7/14/2018 at 2:36 PM, Emile said:

Was wondering if there is a speaker switch that can be used with tube amps ... not even sure if it possible since the tube amps require an ohm load :( Any switch would temporarily disconnect.

But :D getting a new (old) pair of KP-3002's and wanted to try those with my Bob Latino VTA ST70 (without unplugging my Forte's).

Many thanks for any inputs!

Cheers, Emile

Yes, simple but it must be done with speakers of the same impedance rating, lets assume 8 ohm ones, and done with a separate switching box and not part of the amplifier. Tube amplifiers have output transformers with a specific load assigned to the outputs. Some have taps for an additional impedance lets say 8 ohms and 16 ohms as an example. To do it as part of the amplifier you would have to have another set of output transformers installed on the amplifier, not a practical addition. All you need is a speaker selection box that is sold at many locations. An example would be a Best Buy audio selection listening room where one can switch between speakers for comparison using the same amplifier.  

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Guest wdecho
20 hours ago, Schu said:

that's an interesting question... I would like a solid answer also.

I wonder if it's the same thing as having a switchable (triode/pentode) PP amp?

No. That kind of switching just removes or adds a component, components, inside the circuit of the amplifier. One would need to see the specific schematic of the said amplifier to understand what the designer used to achieve this. Usually not complicated at all from the schematics I have seen. 

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Here's my 2 cents:

Terminate the speaker cables with banana plugs. Wire the amplifiers' speaker connections to one of these:

http://www.vadcon.com/pp/pps16-bbgs.html 

http://www.vadcon.com/pp/pps8-bbns.html

With the amplifiers powered off, you simply plug whichever speakers you want into whichever amp you want.

Use something like a Niles AXP-1 to switch the RCA output (e.g., from CD player) between the amps.

This can serve many amps, and many speakers, and has no amp power limitations, and no concerns about frying an amp because of what's going in inside a box.

I have this installed in several systems. Works great.
 

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11 minutes ago, robert_kc said:

With the amplifiers powered off, you simply plug whichever speakers you want into whichever amp you want.

Thanks ... but I am lazy ... wanted to see if I could "hot switch." :D 

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If switch is "Make- Before- Break" wouldn't that work? For an instant(in the order of milliseconds) your two 8 ohm speakers would present a 4 ohm load to the amp. I am not a tube amp guru but a momentary lower impedance load would be preferable to a open load?

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I don't know nuttin' about this subject, but intuitively say "don't do it"!  Just turn off the amp(s), let cool a bit, do the switching, and only then turn things back on again.

 

I reached up to turn off my tube (Joule Electra) preamp a few weeks ago, lunged at the switch as my balance faltered, apparently sent a rapid on-off current into just the pre, heard a "POP" thru the speakers, and spent the next 2 days looking for the right fuse size, and finding someone to climb up and find and replace the preamp fuse -- after I finally got a pic of where the effing fuse box was so I knew where to find it.  And, this was just WITHIN a single tube unit, didn't even involve switching between more than one unit!

 

I'm very leery of sending unexpected current surges into tube equipment.  It takes too long to trouble-shoot some of these things.   It ain't worth it.

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13 hours ago, Emile said:

Thanks ... but I am lazy ... wanted to see if I could "hot switch." :D 

 

Hot switching is fine as long as it’s done under zero signal conditions (i.e. no signal to the amp input).  I don’t know how the myth got started that tube amps must have a load connected at all times to prevent them from blowing up.

 

Maynard

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