Valve life & changes

[MartinS]

I have a pair of Icon MB90 monoblocks that are just over 3 years old which I have owned for a couple of months. This is impossible to answer exactly, however by my reckoning the KT150s have probably done 2500 hours as a guess, so is it about time to consider changing them? Thus far they seem fine and they aren't showing signs of low emission but I would rather change them before there is a big bang.

The input valve is a 6SL7, I have a pair of Sylvania JAN which could be NOS made in 1951, any good? The phase splitter is 6SN7/CV181, what might be a good recommendation for this. I have a pair of new Psvane CV181 but if theres a better suggestion I'd certainly consider it.
Regards
Martin

[Filterlab]

I have the Sylvania 6SL7s in the cupboard. They're ok. In my experience however, the best 6SL7 I've heard is the late 50's RCA 5691 Red Base black plate. I use a pair of NOS in my buffer stage. Pick up a NOS single for around £60, or a NOS tested matched pair for £120-£130; they're getting rare though.

Also excellent is the Melz 6H9C metal base from the 50's. Superb valves and they're more numerous. Grab one for about £40 from Russia or Ukraine on eBay, a NOS tested matched pair for around £90.

[MartinS]

Bob
Thanks for the thoughts, I have substituted the Sylvanias for the Tungsol gold pins. There is a difference, the top has opened out compared to the Tungsol ones though they weren't too bad. I don't doubt the RCA 5691s would make a difference as well, whether enough to justify the cost is debatable. I think I might do something re the 6SN7 phase splitter, currently Psvane CV181 (which might actually be 6SN7), Shuguang Black Treasure seem well thought of but thats another £143 plus postage, again whether the fairly minor change justifies the expense is frankly open to question.
Regards
Martin