Can you do anything to make power tubes last longer ?

You just align the needle with a black dot, no red/green lights.

These Mullards are not excessively warm, though of course on the warm side. Just as my entire system is, including the speakers. So the match appears to be perfect.

Good points by @atmasphere and a couple I want to comment on.  My current amp has a warmup relay to warm the tubes up before applying B+.  What he suggests with a warmup switch is easy to do and a great suggestion.

Avoiding high voltage is important.  The designer was very careful to provide the correct voltages and if your voltage goes up 120 to 125 (mine varies from 117 to 124 and that is just what I have seen) then the increase goes right through the power transformer to every voltage in the amp. 

A good way to regulate voltage to 120 (I have mine set to 119.9) is with a regenerator.

Jerry

@inna congrats on finding the Mullards at hopefully not too an outrageous price. I’m sure you’ll be very happy you did. I had similar experiences, though different amps but the same tubes, and found that the SED never gave me as good an experience as true Mullards. Ralph brings up a very good point of warming up the tubes slowly at the outset. It’s probably (at least one of) the reason he builds his amps the way he does.

marco1, thank you.

Yes, so now I have 12AX7 Mullard long plates in the preamp, 12AU7 RCA black plates in the driver and Mullard EL34 XF2 power tubes. This is done. Now I will have to think/experiment what to put in the phono stage, since I don't care much for the Brimars that are currently there.

The price was reasonable. A little more than new SED tubes cost.

I’ve always liked the RCA 12au7 black plates. I remember discussing them on another thread with you and Mulveling. I’m currently using RCA 5816A black plates as a driver in one of my amps. They’re a little more refined and warmer than the 12au7 and although I’ve never used them in combination with Mullards EL34 I think they would compliment the Mullards nicely.  Something else to spend your money on if/when you get the itch 🤑