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SS to Tubes and back switch


Kidd

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13 hours ago, jimjimbo said:

Not as easy as you might think.  Tubes require a load (speakers) to be connected, while SS does not.  You can damage a tube amp if you don't have a load connected.

 

Under zero signal conditions there is no concern about operating a tube amp with no load.  

 

13 hours ago, Kidd said:

Something like the  A&B switch on a receiver for speakers.

How 'bout a switch box thingy to go back and forth between SS amp and tube amp to hear the difference ,  what to use ???

Kidd 

 

Go on to the Niles Audio site or check Parts Express.  They both offer all kinds of switch boxes which would allow you to do what you want.  

 

 

Maynard

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2 hours ago, jimjimbo said:

What exactly are zero signal conditions?   Wouldn't any source or preamp generate some kind of input, however minimal?

 

Typically, zero signal would be without any sources connected.  However, simply turning down the volume control of an integrated amp (or volume control of a connected preamp), having a cd player connected and turned on but not playing music, etc. are quite fine as well.  A trace amount of signal leakage isn't going to cause any harm.  In the service world it is often necessary to leave an amp "cooking" on the bench for hours without having a load connected. 

 

I think the philosophy behind having a load connected at all times originated with some very poorly designed amps which broke into ultrasonic oscillation without a load connected which could possibly affect the output tubes.  Given that virtually all single ended and push-pull amps using pentodes/beam power tubes have an ample amount of negative fb, it isn't a concern.  Triodes, in my experience, are immune to open circuiting. 

 

 

Maynard

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3 hours ago, richieb said:

 

=== I was always under the impression the load seen from a tube amp, or any amp I suppose, is being connected to speaker outputs? I have read on more than one occasion in tube amp manuals to “ do not turn on without speaker leads being connected”. ?

Yep, that's what I was referring to, and what Maynard responded to....

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17 hours ago, richieb said:

 

=== I was always under the impression the load seen from a tube amp, or any amp I suppose, is being connected to speaker outputs? I have read on more than one occasion in tube amp manuals to “ do not turn on without speaker leads being connected”. ?

 

The load impedance the tube "sees" (reflected from the opt secondary) when a signal is applied is an AC phenomenon.  At idle (i.e. zero signal), the tube is sitting at its quiescent operating point which is a DC condition.  The recommendation to always have a speaker connected is designed to avoid a situation in which a person plays  music, turns up the volume control, and leaves it that way while figuring out why there is no sound.

 

 

Maynard

 

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