Amp switcher with tube amp protection
In terms of the Specialty-AV SP-71, any idea if the resistors have an effect on your sound? Or do they only get "activated" when you switch to the other amp?https://forums.audioholics.com/forums/attachments/20190218_165752_zps9eahesvq-jpg.28295/ Four resistors connected to both inputs, so it is "activated" to both amplifier at all times. Those resistors consume less than 1/10 of the amplifier output power, IF you want to switch amplifiers in your system, this is the necessarily compromise, but I doubt you can hear the effect. BTW, solid-state amplifiers usually are safe to stay on without load, you can disconnect those resistors on the AVR side. |
Also interesting to think about, the amount of music vs. tv usage, and limiting turning the amp on and off. During the week I typically use my system for a couple of hours of tv each night. During the weekend a mix of music and tv. So I guess in my case solid state during the week, tubes for the weekend. In terms of the Specialty-AV SP-71, any idea if the resistors have an effect on your sound? Or do they only get "activated" when you switch to the other amp? |
You need to consider your music listening vs. tv watching patterns. Tubes will last a lot longer if left on for slightly longer periods than frequent power ups and power downs. If you listen to music 2 or more times a day, broken up with a period of watching tv in between, your tubes will be better off staying fired up. I’m in the same position as you - I use the same area for movies and music. I fire my amps up at around 9am every morning and they stay on til 1 or 2 am the next morning. I use the tube amps for both music and movies. I have done that for many years - no problems. I have not used up a power tube yet. |
The most simple way to protect your tube amplifier output transformer is
connect a 5Watt 100Ω
- 150Ω
resistor across the "+" and "-" speaker output binding posts of your tube amp, either 4Ω
or 8Ω tap is OK,
it will provide
some load to the tube amp when the speaker is disconnected.
https://rukminim1.flixcart.com/image/416/416/kgfg2vk0/resistor/j/v/r/100-ohm-5w-wire-wound-resistors... There also a switcher with built in loading resistors: https://www.amazon.com/Amplifier-Receiver-Speakers-Selector-Switcher/dp/B0796KGVXT |
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I used to run mono tubes; tube receiver; SS. I put 6’ runs from my speakers to female banana connector to receive male bananas. a hook on the wall behind so I didn’t have to bend too much. each amp it’s own speaker wires with WBT tightening banana plugs which are OFC copper http://www.wbtusa.com/pdf/0645.pdf these are similar, but brass https://www.amazon.com/Locking-Speaker-Connectors-Terminal-Connector/dp/B0811LF7BW/ref=sr_1_3?crid=1... some nice pure copper wire https://www.amazon.com/InstallGear-Gauge-Speaker-Wire-Oxygen-Free/dp/B079VJXN1Z/ref=pd_bxgy_2/137-61... I make my own speaker wires from OFC Cat 8: 22ga x 8 = 13 awg. a source popped up https://alitools.io/en/showcase/hifi-audio-4pcs-mca-ofc-gold-plated-banana-lock-plugs-hifi-speaker-b... |
Thanks for your great explanation, makes sense to me even without much proper knowledge of electronics. For me to build this would maybe be a bridge to far at the moment though. Although it sounds like a cool project, making a nice casing etc. I just don't have any tools to do this, plus would be afraid to mess it up and fry my amp 😅 I find it hard to believe there aren't any commercial solutions though. It doesn't seem like a crazy rare use case to me? |
Problem is when the SS is switched to speaker position the tube amp has no resistance. Accidentally turning on the tube amp while not connected to a speaker load will damage the output transformer. There is a workaround, although it requires a bit of design and construction (I know of no switch that can do this). You will need a three pole double throw switch (position A and position B or ON-ON) with a rating of at least 20-amps. You will also need a box with two pairs of binding posts (call them A and B) on one side for the amp hookup and one pair of binding posts on the other side for the speaker hookup (call this COMMON). Let’s say position A is the tube amp and position B is the SS amp. I suggest you look at a wiring diagram of a 3PDT switch.... Pole 1: Connect pole 1 common to the speaker negative binding post, position A to the Tube amp negative binding post and position B to the SS amp negative terminal binding post. Pole 2: Connect pole 2 common to the speaker positive binding post, position A to the Tube amp positive binding post and position B to the SS amp positive terminal binding post. Pole 3: Connect pole 3 common to the pole 1 common, which will ground pole 3 to the speaker negative terminal. Connect an 8-ohm resistor between position B of pole 3 and position A of pole 2. This will put the 8-ohm resistor in series with the Tube amp positive terminal and negative speaker terminal, protecting the amp. Position A of pole 3 is left hanging unconnected. When you switch to position A, the tube amp is connected to the speakers and the SS amp and the protective resistor are connected to nothing, so the tube amp is the only hot circuit with the resistor having no effect. When you switch to position B, the SS amp circuit is hot and the tube amp is protected by a circuit with an 8-ohm resistor, so if you accidentally turn on the amp nothing bad will happen. (This is for one channel. For both speakers you will either need two of these or a 6-pole double throw switch with everything above times 2, i.e., poles 1,2,3 = poles 4,5,6). |
