Standby Switch as a Speaker Kill Switch?

[Alexo]

Hello hello,

So I'm building a bass amp for a client. He wants a line out so he can use it as a recording preamp, which is fine. He also wants a "speaker kill" switch so he won't have to hook it into a cab under these circumstances.

Soooo... I've been pondering this for a while, and I've been thinking of just using a DPDT switch for the standby: when it's on, all will be normal, when it's turned off, it will interrupt the connection between the power supply and the output tube plates and screens, inserting a 240K or so resistor between these tubes and their power supply nodes to avoid cathode poisoning. The switch would leave the connections between the power supply and the preamp tubes unaltered.

I'm using Zeners for the 300 volt drop between the plate and screen/preamp supplies (6550's at 600 volts) so the preamp voltages shouldn't go haywire when the current draw on the power supply is changed like this. SS-rectified, btw.

So my question is concerning the don't-turn-an-amp-on-without-a-load rule:

Can you disconnect the load if you still have a couple volts on the plates via the 240K resistor between the OT and the plate supply? ...and of course a 240K between the screens and their supply.

I'm thinking this will be fine, but it never hurts to have a reality check ...unless it blows up your OT.