The problem is that vacuum tube amplifiers can be damaged or destroyed if powered on without a load on the speaker terminals. Therefore the switch should not only switch amplifiers, but also switch the unused amplifier to a dummy load to protect the vacuum tube amplifier in case you accidentally leave it on - or turn it on.
[Edit: After more research, I discovered that the danger from no-load on the output transformers amplifiers of a vacuum tube aplifier is probably not an issue for many configurations and situations, at least when the amplifier is an ultralinear tetrode, pentode design utilizing negative feedback (NFB), not operating in triode mode and not driven into clipping. See more on this in my February 16 post below.]
After an extensive internet search, I found many source/amplifier/speaker switches, but none with tube amp protection. However, I did discover a little Canadian company in Ontario that builds vacuum tube amplifiers and custom switches. (An additional benefit is that their design style would complement my black with wood panel YarLand amplifier very nicely.)
I sent them the below email, and invite ASR members and visitors to watch or join my quest.
[Edit: After more research, I discovered that the danger from no-load on the output transformers amplifiers of a vacuum tube aplifier is probably not an issue for many configurations and situations, at least when the amplifier is an ultralinear tetrode, pentode design utilizing negative feedback (NFB), not operating in triode mode and not driven into clipping. See more on this in my February 16 post below.]
After an extensive internet search, I found many source/amplifier/speaker switches, but none with tube amp protection. However, I did discover a little Canadian company in Ontario that builds vacuum tube amplifiers and custom switches. (An additional benefit is that their design style would complement my black with wood panel YarLand amplifier very nicely.)
Mapletree Audio Design [LINK] offers a unique range of designed and hand crafted by Dr. Lloyd Peppard and Dr. Al Freundorfer, both electrical engineering professors. Our goal is to foster the enjoyment of recorded music through the use of vacuum tube amplification and signal processing, offered at a reasonable price.
I sent them the below email, and invite ASR members and visitors to watch or join my quest.
To: Mapletree Audio Design:
As you know, vacuum tube amplifiers can be damaged or even destroyed if turned on/operated without a load on the speaker outputs.
Therefore I am looking for a two-amplifiers to one pair of speakers switch box with XLR input and output, and 5-way speaker connectors, using high-quality (but not esoteric) switches and connectors. I will use my 100wpc ICEPower SS amplifier for HT/Video use plus casual background listening, and my PP, Class A, EL34/6CA7 YarLand vacuum tube amplifier for dedicated and focused music listening.
When switching amps, I want to protect the tube amplifier in case it is accidentally left on when switching from the speakers to the SS amplifier.
The core of my requirements is to switch the vacuum tube amp to a dummy load (internal or external resistors, or a pair of super cheap tiny 8Ω speakers), thereby protecting the tube amp from damage if it is left on. It would also be nice to have a flashing red LED warning light (by-passable) if there is current from the tube amplifier to the dummy load indicating that the tube amp is powered on when the SS amplifier is being used.
Of course, some tube amp aficionados want to leave their amps on, and a dummy load is mandatory, but unlike Class AB amplifies, Class A vacuum tube - and SS amplifiers - are so energy inefficient and hot-running, that I want to save energy and reduce heat by turning the amplifier off when not using it.
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