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kt88 tubes

karma67

pfm Member
an interesting one,
ive just replaced my gec kt88's (quad) with sovtek kt88's. now i know the gec's are supposed to be the holy grail of kt88's and command huge sums but im not hearing a huge drop in the sound,infact the sovteks seem to have a bit more omph to them,there is a subtle difference in clarity in favour of the gec's at the moment but the sovteks need some hours on them.

the price difference is 4 gec's £1000+ and the sovteks were £90!
do different brand power valves really make that much difference to the sound,at the moment i think not.
 
an interesting one,
ive just replaced my gec kt88's (quad) with sovtek kt88's. now i know the gec's are supposed to be the holy grail of kt88's and command huge sums but im not hearing a huge drop in the sound,infact the sovteks seem to have a bit more omph to them,there is a subtle difference in clarity in favour of the gec's at the moment but the sovteks need some hours on them.

the price difference is 4 gec's £1000+ and the sovteks were £90!
do different brand power valves really make that much difference to the sound,at the moment i think not.

Just as I've always said! By far the greatest differences between output valves are in reliability.... not sound....
Which is as should be expected as the circuit topology, output transformers and amount of NFB mainly decide sound quality. If your amp is much above say 60WPC don't expect them to be anywhere near as reliable as the GEC's...
Oh and don't touch Chinese KT88's with a barge pole! Even "posh" ones like Psvane etc. The Russian clone versions of GEC Gold Lion/Golden Lion seem about the best current KT88's from my limited experience of them.

Obviously the difference between worn out valves and new ones can be an impressive "upgrade"!
 
its pushing 115 watts :eek:

Even back in the day the specced very max for GEC KT88's was 100W IIRC! If they last 3 months you've done well....
A sudden loud crack as one arcs over inside followed by blown fuse is the likely failure mode IME. The "weakest" "most Mon morning/Fri afternoon" of the 4 being the one to go.
You may be lucky... for every half a dozen tales of modern ones lasting only a few months in high power usage I hear a tale of "well I used those valves and they were fine for the 3 years I had it"... it's very much a lottery...
 
gawd knows,it was measured by john caswell when he put the gec's in,after repairing it because 1 of the original (to the amp) sovteks blew and took out a cap and resistor
 
200W with Gallium Nitride FET transistors


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gawd knows,it was measured by john caswell when he put the gec's in,after repairing it because 1 of the original (to the amp) sovteks blew and took out a cap and resistor

Ah yes will often also take out the screen grid resistor of the valve that goes... (blown cap is unusual). This is what I see time and again... one valve arcs across inside, loud crack, fuse goes, often screen resistor goes, owner puts new fuse in and tries it but fuse goes again often with another crack.... I fix amp and give them 3 part worn KT88's back after binning the duff one... classic scenario!

It's a brave man uses anything other than real GEC in a KT88 amp putting out anything much above 70- 80WPC
 
I've used KT 88s in my Audiopax for, a long time. GEC's a lottery buying used as I found to my cost, E.A.T.s, overpriced crap, JJs fine but spectacular when they go, Electro Harmonix, in situ for the last few years and nice enough but a sad day when Sovtek stopped making KT 88s. By far the nicest and most reliable I've had in my amps and the nicest looking:)
 
Electro Harmonix is Sovtek....

I've found JJ's to be awful in the past and I won't use them but it seems they have vastly improved their QC in the last ten years or so and they may be fine now. I still don't use them though. A JJ EL34 in which the glass melted was the last straw!
 
A possible "get around" for top KT88's.... but probably too many know by now and so long gone... is that the TT22 IS a KT88 of top quality but with a different pin-out and top cap anode. yes an amp needs "re-wiring" to use them...
 
out of interest jez what sort of hours would you expect to got out of nos gec's, i bias them at 35mv
 
Electro Harmonix is Sovtek? Might be the same manufacturer but the tubes bear no resemblance to each other. As an aside the topmost part of one of my Quad glows much brighter than the rest. Same happened with the delivered tubes, guy at Hotrox sent a replacement but said it was nothing to worry about. Measure ok, sounds ok but makes me uneasy!
 
out of interest jez what sort of hours would you expect to got out of nos gec's, i bias them at 35mv

Bias should be a figure in mA. I suspect that's a voltage across a cathode resistor but without knowing it's value...

Valve life is pretty much "how long is a piece of string"... how much worse than new do you let them get to before declaring them worn out? Even GEC can just fail of course and it is quite common for a valve to eg "go soft", filament failure, or internal arcing before it gets so worn as to be unusable. As with a worn stylus it is very gradual and often one will change the valves "to be on the safe side" only to be stunned at the improvement!

Probably in the range 1500 - 4000 hours

You could get lucky with the Sovtek ones of course... and if they do go (well usually one goes) replacing a screen resistor and fuse is no big deal.
 
Electro Harmonix is Sovtek? Might be the same manufacturer but the tubes bear no resemblance to each other. As an aside the topmost part of one of my Quad glows much brighter than the rest. Same happened with the delivered tubes, guy at Hotrox sent a replacement but said it was nothing to worry about. Measure ok, sounds ok but makes me uneasy!

Sovtek, Electro Harmonix and post "Winged C" Svetlana are all brand names of New Sensor Corp of New York. Many are identical valves whichever branding they have and other valves are only sold under one branding.

The differing glows are nothing to worry about.
 
Bias should be a figure in mA. I suspect that's a voltage across a cathode resistor but without knowing it's value...

Valve life is pretty much "how long is a piece of string"... how much worse than new do you let them get to before declaring them worn out? Even GEC can just fail of course and it is quite common for a valve to eg "go soft", filament failure, or internal arcing before it gets so worn as to be unusable. As with a worn stylus it is very gradual and often one will change the valves "to be on the safe side" only to be stunned at the improvement!

Probably in the range 1500 - 4000 hours

You could get lucky with the Sovtek ones of course... and if they do go (well usually one goes) replacing a screen resistor and fuse is no big deal.

yep its measured across the 1 ohm resistor,35mv on my meter = 35 ma, i hope thats correct?
 
yeah ive been reading that and came to the same conclusion,i asked the maker of the amp (john wood) a while back about that and he confirmed 35ma.
would the low figure have anything to do with what type of circuit is used? ie push pull,ultraliner etc? it uses 4 kt88's by the way
 


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