Can I please borrow your collective brain power?

still have to turn the unit on, which then powers all the tubes . is my guess

Best guess (from looking at a picture of the inside) is that all the tubes remain in play. The only thing that bypass switch bypasses is the selector and volume control. At best, only one tube is taken out of circuit. However you just can't remove tubes. This will start to raise the voltages on the other tubes.

It is designed to run with all those tubes, so that's how it should be run.

Something has to supply the gain, Something has to drive the 300B, and the 300B drives the 805.

Those tubes are Driver/Input tubes. A separate power amp also has Driver/Input tubes. The bottom line is you need those tubes.

Are you trying to defeat the heat?

If so forget about it.

Go buy a Class D or a AB Integrated.

No matter (PDS) if this is being used in an integrated or power amp function all tubes will be energized and creating heat.

Preamps typically use the little tubes that produce little heat and cost. If the unit works without the preamp tubes (my guess is it will not)… it will probably not reduce the heat by any appreciable amount. So, if you just want to use as an amp, I would do that. The little tubes last longer and typically cost little.

Thanks, all.

I was curious.  Seemed a waste if they were unnecessary to have them in there.

I’ll leave them.

Cheers.

Don't think all are actually used, but I would certainly leave them in because that is how the amp was designed to operate. That is unless you know something the designer doesn't. 

Six (6) captchas in a row, BYE.

According to a review i read the preamplifier section is passive ( no tubes or preamplifier section ) so all the tubes are on the power amplifier section. 

JerryG above is right. These put out a lot of heat and all tubes are always in action.