Dummy load for valve amp on speaker cable?

[Rug Doc]

I have a valve amp that I would like to use occasionally, I would like to have the cables in place and be able to switch the speaker cables behind the speakers when I want to listen..

I understand that if the amp is powered on with the cables inadvertently disconnected it might damage the output stage, so can I put a resistor across the cables permantly so when disconnected there's still a load on the amp? Would doing this effect the loading of the amp enough to effect SQ and be audible?

 

[Arkless Electronics]

No. You need it to switch the dummy load in and out as required. The obvious answer is don't switch on the valve amp when it's not selected by speaker switch.

 

[Rug Doc]

Thanks Jez. I'm looking at some switching boxes, but they're hundreds of pounds! trying to see if I can do it a bit cheaper... All I want is a switch box, one set of speakers output, two amps in and a make before break switch with a dummy load for the vale amp when switched out..

 

[earlofsodbury]

Simplest thing to do is use a make-before-break switch, that way the amp always sees a load.

I believe it's a bit of a non issue in your case, because the effect of running without a load upon the power valves and OPTs is not instantaneous - it takes a short period of time for the OPTs to saturate and feed back enough HV to take out the power valves. A momentary disconnection while switching with a normal single-throw switch wouldn't be long enough to cause any harm.