Life of KT88's

[bikerhifinut]

Not sure if this is the right section.
Can anyone give an idea of expected service life of a KT88 valve?
With particular reference to the WD88VA as I imagine they'll last longer in that design due to being under run?
They seem to be extremely expensive valves to replace, and theres not many choices of KT88 on the market anyway. I'd have gravitated to the Svetlana ones anyway as my limited experience has been that the better Russian valves are of superior quality to most other new manufacture devices.

[John T]

Power valves average 2000 hrs and small signal types 5000-10,000 hrs.

[bikerhifinut]

Originally Posted by John T

Power valves average 2000 hrs and small signal types 5000-10,000 hrs.

Thanks.
so about 2 years i reckon as I tend to use the hi fi every day.

[Black Stuart]

I bought a supply of Svetlana KT88s and 6550s from Igor Popov in Bilbao.

This man used to have his amp designs on the old Svetlana site and he reckoned against all other opinions that if run moderately these valves would last for years.

It also helps if your amp has 'slow start-up'. Because I've had problems with my KAT88 amps (Greg knows this very well) we have been using my partner Angela's KEL34 (heavily modded) with no slow start-up for 7 years on and off here in Spain, I refuse to use it in the summer since we moved to behind the Snowy mountains because of the temperatures which prevail in the summer, today it is 45C.

The same set of Svet EL34s have been used now for over 5 years and I cannot detect any degeneration in performance.

Small signal valves 5-10,000 hours maybe, again how many times a day is the amp fired up and does it have slow start-up?

I am a fan of the mil. spec. 6SN7s these are rated at 10,000 min. it all depends on how you run them and at what temperature.

It seems incredible to me that professional/amatuer amp designers never take into account - operating temps - do they have a blind spot here - it would seem so. The whole shape of traditional amp chassis is stupid when you think about internal temps.

A Dutch friend is experimenting with using the best PC fans. Lowering the internal temperature will definately lengthen component life, probably double them and the amp will sound better as well - what more could you want.

[pre65]

Originally Posted by Black Stuart

A Dutch friend is experimenting with using the best PC fans. Lowering the internal temperature will definately lengthen component life, probably double them and the amp will sound better as well - what more could you want.

Hi-i hope they are quieter than the ones in my PC !

Not a day for a sweater then !! 45 degrees = hot

Philip

[John T]

Originally Posted by Black Stuart

It seems incredible to me that professional/amatuer amp designers never take into account - operating temps - . . . . . .

Good point Stuart. This adds credence to your comment.

John.

[Black Stuart]

Philip,
45C is'nt hot, it's bloody hot.

Papst are the quietest fans, I don't have the actual model no. to hand, used with a variable DC voltage Tx, they are so quiet as to 'not be there'.

They can be bought direct from Germany, post free within Europe (that may mean mainland Europe).

Two of them mounted in a frame are being used beneath a Bada h/amp and they have totally cooled both the 6SN7s,the mosfets and of course all the caps and resistors. So the life of all components is seriously lengthened and looking at the article that John T posted, some hugely so.

The upshot is that as Tourmaline uses the mil. spec. 6SN7s they really should have a 10,000 hour + lifespan.


We intend to use them with all our amps. Ironically had I been able to build my own house here in Spain I would have used an alternative cooling system drawing in cold (or cooled) air from outside. Southern Spain would only have entailed a little ingenuity using air drawn through a finned aluminium pipe laid inside an underground water source, with a reasonably powerful (it would depend on the length and diameter of tubing used) fan installed outside.

This fan cooling system could be further refined by shaping material around the amp to induce production of a convection current, maybe even negating the use of a fan at all, except for summer use.

I think it could make a very good project for a university engineering dept.

Apparently the fans and Tx cost around E60, this is a small price to pay to save a lot on component replacement and increased performance from our amps.

The big challenge is to build amps from a totally different perspective and therefore layout.

Steve Poskitt built a lovely little two box affair with his EL84 SE amp. Seperating Txs/PSU section from the signal circuitry is a common sense way to begin, cramming everything into a little boring rectangular box is stupid, dull and plain ugly - that's why so many women and a lot of men are turned off from hi-fi and onto compact mini systems - they mostly sound **** BUT they look good.

Ban the ugly box is what I say - it simply does'nt have to be this way.

[Tourmaline]

Originally Posted by pre65

Hi-i hope they are quieter than the ones in my PC !

Not a day for a sweater then !! 45 degrees = hot

Philip

Hence the choice of papst fans AND a 12 volts converter wich can be switched from 3 volts to 12 volts. The papst fan can be run from 7 to 12 volts. So, you can determin wich is the best setting for cooling/sound production. Papst are known for their quality and very good cooling at low speeds.

[pre65]

Hi-thats interesting,pity they wont run from 6.3v !

Philip

[Black Stuart]

Philip,
that's why you need a seperate DC Tx, what's the problem, it's so easy.

I'm lucky I can and will visit the stonemason and specify what shape I want the slate or snakeoil stone uplifters to be, so I will only need the two fans and they will be transferred from h/amp to power amp as required.

As Tourmaline has found using them raises the quality of the sound produced.

£40 or so for better sound and hugely increased life of components has to be a good deal.