You can use them as rectifiers.
Frank Cooter has used mercury vapor tubes in his builds. High cool factor.
As I mentioned it a while back, here is a super small Stax tube amp.
Design isn't finalized yet but this thing will not swing a whole lot of voltage (500+Vp-p) or be very powerful but it is cheap and cool. The small PCB in the back is the HV supply which is driven off 12VDC which also powers the heaters. It's a switcher but it was very cheap. Fully balanced from input to output but not really portable as it needs 12W just to light up the tubes.
Would never work unless you want to stick a Stax logo on some high power DC lines? 300B's will glow blue sometimes and some other DHT's too. There will be a 300B based Stax amp or two...
I posted the following elsewhere, but someone suggested that I should post it here. Sorry for the double posting. I would really appreciate all the help I can get, whether it's about fixing the driver or getting a new one. I love my Lambdas, but am not capable of buying a completely new set.
I have a pair of 6-pin Stax SR-Lambda that's driven by an amp + SRD-6. The left side, however, has minimum bass. There is little channel imbalance or any observable distortion on the left side, just a lack of bass. I have switched speaker cables, reversed channels in my computer, even resoldered all the joints on the phones, but still could not solve the problem. I understand that old Stax drivers may develop a channel imbalance, but mine are fine balance(volume)-wise. Any insights as to how I may solve the problem?
It wouldn't be wise for a portable tube amp to use high powered mini tubes when the thing runs off batteries. lol
A 300B Stax amp sounds interesting. I'm all for the pretty tube glow and of cause - good sound.