Sorry Newbie startup question

Just opened the Box to my GM40 Deluxe.

Quick question - Is it OK to start this thing up without a Speaker attached. I have read the bit about the Red Box AE in the Manual and it states that the GM40 detects when a Speaker Cable is unplugged. Does it also know if there is no Cable connected at startup?

Do I start the Amp in Standby or play and then back it off to standby when not using it?
Before anyone asks, waiting on a new Speaker to land in the Post - Just want to see the Blue hue that this thing emits.

Thx.

Benny

Yes, as long as you don't have a speaker cable plugged in the speaker output, you will be fine.
You can do that on the first power on, no problem.
Startup: Flip the Power Toggle to ON, the amp will light up; wait a minute, then flip the Standby toggle to PLAY position. The top of the amp gets pretty warm when used witha s peaker and that's normal. However, running it without a speaker might make it a bit hotter. When not playing for more than 10-15 minutes, go to STANDBY, if finished playing go to STANDBY, then flip the Power toggle to OFF.
Red Box: To be heard you need a standard XLR balanced mic cable (female to male) to connect the red box output to a mixer, or XLR Female to TRS 1/4" jack cable if You don't have a mixer or a home receiver/amplifier with XLR inputs. Make sure that red box is set to ON, and also choose the preferred settings for ambience and speaker type.
Be aware that the Master knob of the amp affects the output level of the Red Box. Be careful not to overload the input of the external device you are plugging into (mixer, receiver, etc).
Good luck!

Silkman has got your back there with his advice.  If I can add a little general info to one of your points it might be of interest for your use of other makes of amp.

Most Standbys work by removing the HT from the output stages, sometimes for the preamp as well but not usually nowadays, while they leave the heaters powered up so the valve is ready to kick into action immediately it is reapplied.  This is not a good thing!  It gradually kills the output valves by cathode poisoning.  This is an atomically thin layer which is built up between the cathode emissive coating and the nickel supporting structure and it builds up an increasing resistance in the cathode circuit of the valve.  It is largely irreversible and the valve is junked.  It's a slow process but it is well documented and is caused whenever the valve is left heated and emitting electrons from its cathode but with nowhere for those electrons to be drained off as a current, no HT means no anode voltage to draw them away.  Google "cathode poisoning vacuum tubes".  (Even Sweetwater knows about it now. )

H&K has a different approach.  In their amps we have the TSC in place.  This is based on having a MOSFET in each of the output valve cathodes.  Under signal drive that MOSFET is effectively fully on and allowing the valve to be in control of the circuit.  With no signal the MOSFET can be used to set the minimum current to the bias level that is needed.  The currents through the MOSFETs are all constantly monitored and trimmed by the TSC control circuitry.  That is why there is no bias adjustment necessary on a H&K amp, the control circuitry balances and sets it accurately for you all the time.  Another benefit of this is that when you put the amp on Standby the HT can be left in place and the current through the valve can be limited to only the plain bias current with no, or at least very little, increase in current in response to a signal.  Now there is no problem with that build up of electrons and the high resistance layer they cause as they are drained away as the bias current.

My advice (and that of many others who know the inside of amps and not just the "common knowledge" which rules all guitar thinking) is, don't even bother with Standbys on conventional amps.  Why do you need them at all?  Vox amps originally didn't have them and, when they put them in place to be "on a par" with other manufacturers, they actually damaged the amps.  They offer absolutely no benefits at all.  They do not preserve your valves from "wearing out" in any way.  They do the opposite and kill them much earlier than they would normally die.  You have a Master Volume control.  Just turn that fully down and leave the amp standing.  How inconvenient is it to have to turn the Master Vollume back up before playing? The amp is then only idling at low bias current so there is no stress or wear on any components at all.  Including the much maligned electrolytics which are another myth driven non-problem if you know them and their failure mechanisms well.

One odd effect of this that H&K users often fixate on unnecessarily is that on Standby sometimes a very faint signal can still be heard at the speaker which is due to a very slight change in current possible around the bias point.  Nothing is absolutely perfect.  To criticise such a good system which achieves so much in terms of managing your amp automatically for a tiny level of sound still possible is ridiculous in my book.  People do still complain that this should not happen, even though it is normally inaudible unless you are in a silent room with your ear very close to the speaker to hear it. The real world rules, or at least it should.

Silkman / Bordonbert, Thanks for the info and taking the time to reply. Benny.

Bodenbert, I've only read a number of your posts as I'm a newbie. You are an Encyclopaedia!
I'll have to read your post ten times to try and get my Head to digest it! Thankyou.

Don't worry too much about understanding all the technical details Benny.  The main thing to do with any informative posts by people like me, or by people who are the "internet guitar guru" types, is to question them.  Don't take any of it as fact just because anyone tells you it is.

If you search for what I mentioned in there, "cathode poisoning vacuum tubes", you will be able to check if what I say is correct.  It is important that you and others know there is other better founded info out there which can be believed which backs up what I (or anyone else) says.  We are living and playing in amongst so much absolutely technically incorrect mythology that it is untrue, but no one will accept the idea that the things their "guitar guru" tells them can be untrue and should be fact checked before believing them.  Have you ever wondered why there are very few genuine electronic engineers, (that is different to a technician who is a specialist in a different field than circuit design), posting on forums like ours?  The reason is that as soon as they put a conflicting idea forward from more factually correct data they are flamed by those who already know that it is incorrect, because "common knowledge" and the other "pedal modders" say it is wrong.  The engineers are not going to preach to those who are utterly convinced they are already saved, they have better things to do with their time.

This is not me impersonating Pres Trump and shouting "fake news" at anything I don't like, this is me putting the more correct information from a genuine engineering perspective, (I've had a lifetime designing circuitry for high level industrial use), in order that you can research it a little and form your own truth based on what you find.  Look at where believing our politicians implicitly just because we see ourselves already on the same side of the argument has got us on both sides of the Atlantic, and in the USSR and in China and...  on forums like this.