[G a f f e r]

Just bought one of these SET valve headamps in pristine condition for only £60 (little previous use). Unfortunately, no box or instructions. So I downloaded the paltry 2 pages from MF website, which gives very little info. Can anyone tell me what valves this uses? I assume it would be about 5-6 years old (being the first version) in which case, when do i replace the valves?
Unlike my standard EL34 valve amp, I was told I should leave this one plugged in (switched on) all the time. Is this safe or will it overheat and reduce valve life? (Basic Q's, I know, but no answers on the MF website).

Thanx for any help.

PS Amp sounds Great at the mo, treble a bit grainy/high on some recordings...probably not helped by my Senny hd575 cans though.

PPS and here it is:

[Nic Rhodes]

I can't remember but I thought it was ECC88s, I will check. If it has hardly been used then they won't have worn out but can be improved (different thing). You can leave it on bu for headphone listening I would just turn on when needed. The valves are not stressed in this design.

[G a f f e r]

Thanx.
You're right, the stock tubes are a type of ECC88 called 6922.
I could also use 7308 or Cc tubes.