Technical Differences Between KT120 and KT150 Valves

[JohnJo]

I've noticed some manufacturers stating that their (normally KT88 equipped) amps can be used with KT120s but NOT with KT150s.

Having had a look at the data sheets I can't see any reason why not but I'm conscious I don't know a big lot beyond checking pin-outs, heater currents and max voltage ratings.

Would some of you learned chaps have a look and advise please?

I can understand that the existing amps may not be optimised for the KT150s but to say they can't be used but KT120s can

My cynical side suggests it's a marketing ploy to promote their new range of KT 150 equipped models but maybe there's more to it than that.





Oops, looks like only the 1st page shows up of these datasheets. Here's the links to the full documents.

http://ww.tungsol.com/specs/kt120-tu...ecs-curves.pdf

http://ww.tungsol.com/specs/kt150-tung-sol.pdf

[dimkasta]

My first guess would be wimpy power supplies

[anthonyTD]

KT120's can be used in place of KT88's in many amps, as long as the power supply, and bias system can accomodate them, the heater current with the KT120's is a little higher ie; around 150, to 200ma more than a regular KT88, However, the surge current is greater, especialy with the KT150's,[in excess of 3 amp initialy] But both the KT120's and KT150's settle down after a couple of seconds though, ie; KT120 1.8 Amp, and KT150 around 2 amp.
Both valves when run at the same parameters as KT88 will be running quite conservatively, so should last longer in the same circuit, however; be aware that KT120's can suffer from loose internals. hence can start producing mechanical noises etc.. Many prefer the KT150 over the KT120 as it seems to produce a more pure sound, this is partly down to the glass shape, which having no parrallel sides much reduces the issue with secondary reflections from the glass being directed back onto the valve structure, and thus being re-amplified etc. Also they have better support of the internal structure.
Hope this helps.
A...

[JohnJo]

Thanks Anthony, that makes sense regarding the increased initial inrush current possibly being a reason why manufacturers aren't recommending using them, might blow a fuse. Transformers are pretty robust things though, should be good for a second or two?

[anthonyTD]

Hi John,
Most well designed mains transformers will cope with the extra Heater inrush, and steady state current of KT120's, However; with the KT150's, you have to be more cautious, and of course add up the extra steady state current each valve demands, ie; if you have four KT88's drawing a steady state current of around 1.6amp each, then the KT150's add around an extra 300, to 400ma steady state current, so' four times 400ma is an extra 1.6amp of steady state current the mains transformer has to supply! This is why KT120's are often recomended as a replacement for KT88's, but not KT150's, due mainly to the extra heater current issues.
A...

Thanks Anthony, that makes sense regarding the increased initial inrush current possibly being a reason why manufacturers aren't recommending using them, might blow a fuse. Transformers are pretty robust things though, should be good for a second or two?

[JohnJo]

Hi John,
Most well designed mains transformers will cope with the extra Heater inrush, and steady state current of KT120's, However; with the KT150's, you have to be more cautious, and of course add up the extra steady state current each valve demands, ie; if you have four KT88's drawing a steady state current of around 1.6amp each, then the KT150's add around an extra 300, to 400ma steady state current, so' four times 400ma is an extra 1.6amp of steady state current the mains transformer has to supply! This is why KT120's are often recomended as a replacement for KT88's, but not KT150's, due mainly to the extra heater current issues.
A...

Yes, I'd read that the KT150s draw a higher heater current but the specs in the data sheets are virtually identical!

I love the extra bass, separation and dynamics the KT120s offer me over KT88s but find a little harshness in the upper mids which I believe the KT150s address, so I 'm exploring my possibilities

[hifinutt]

i am listening to the arc d70 and it has kt120 and not a hint of harshness . the ref75 original had 120`s and seems to receive rave reviews . the se version has kt150 I believe

[anthonyTD]

I agree, I have used both the KT120's, and the KT150's in my own equipment, and I dont get the harshness others speak of with either valve, I guess its system dependent, needless to say; both valves are very good.

i am listening to the arc d70 and it has kt120 and not a hint of harshness . the ref75 original had 120`s and seems to receive rave reviews . the se version has kt150 I believe

[JohnJo]

Great feedback guys, thanks.

[Marco]

Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality.

Like the new sig, Anthony - very true!!

Marco.