Difference 300B / KT88 ?

[Marco]

so...
a good push pull kt88 is a good introduction into valves, when used with more 'normal' speakers,
but as marco has come to realise, there are further gains to be had with higher effeciency speakers that match well
its a slippery slope

Indeed, Steve, but as you know having heard it, the KT88-based Copper amp I use works even better with some quality high-efficiency speakers on the end than it does with 'normal' speakers...

This proves that when a valve amplifier design is 'right' to start with it doesn't matter what speakers are used - the results are still fantastic!

It brings us neatly back to implementation and how significant it is in the overall scheme of things, because that wouldn't necessarily be the case with 'normal' or 'bog standard' KT88 amps and high efficiency speakers... So one must always remember that the key to success is not focussing on any one aspect of valve amplifier design but: implementation, IMPLEMENTATION, IMPLEMENTATION!

Marco.

[SPS]

Indeed, Steve, but as you know having heard it, the KT88-based Copper amp I use works even better with some quality high-efficiency speakers on the end than it does with 'normal' speakers...

This proves that when a valve amplifier design is 'right' to start with it doesn't matter what speakers are used - the results are still fantastic!

It brings us neatly back to implementation and how significant it is in the overall scheme of things, because that wouldn't necessarily be the case with 'normal' or 'bog standard' KT88 amps and high efficiency speakers... So one must always remember that the key to success is not focussing on any one aspect of valve amplifier design but: implementation, IMPLEMENTATION, IMPLEMENTATION!

Marco.

Spot on Marco.. that was my point really.. there are good and bad in everything, and implementation and selection the right components for a task is key... we could be talking about the way an amp is made... or the speaker/ amp / room combinatation.. or any thing else come to think about it..

Another point is that if one gets into valves and one is then lucky enough to get exposure to what good hi eff speakers can do.... it can change your perception of hi fi...

there are many good amps about..
more depends on your budget (and diy skills....if your brave)

what did you think to those mullard valves i left you with?

steve

[Marco]

Indeed so, Steve!

what did you think to those mullard valves i left you with?

They were Osram, and I like them! PM me with the price (bearing in mind my special discount ) and I'll sort it out

Marco.

[NRG]

Just wondered what the difference from the designer's point of view was between these two valves, especially for SETs

I detect a slight preference for KT88 on this forum. The 300B is a genuine triode, the KT 88 was never meant to be ( so someone told me ! )

The Beam Tetrodes or Kinkless Triodes where designed for audio from the outset IE low third harmonic and very low higher order harmonics (5th) all other valves where designed with something else in mind. I like the 300B, many of the SET guys don't but in a PP configuration they work well given a good cct like the original WAD 300B design...where many ccts fall down is in the driver stage, triodes have a lower input impedance and demand more from the driver stage IE large enough voltage swing. The design of the driver stage becomes more critical than the stage for the KT.

Also, the 300B power o/p is generally lower than that of the KT, the 300B grid would have to be driven positive to get any where near (this is where the likes of the 811 etc score as they are designed to be driven into class A2) and it's not really designed for that.

Another consideration is feedback, the 300B has a natural low output impedance without feedback and therefore its damping factor is relatively low, making it usable in zero feedback designs. Zero or low feedback makes for a very open and natural sound, many like this type of presentation.

The KT on the other hand can also be used without feedback but the o/p impedance is really too high like this so either local or global feedback is used to lower it. Adding feedback though alters the transfer characteristic of the amplifier and given a highly reactive 'speaker load the amplifier response can start to take on the same shape of the 'speaker...but feedback tightens the lower registers and narrows the sound stage, many prefer this type of presentation.

A mainly resistive and efficient 'speaker tends not to highlight these differences but use a high;y reactive 'speaker with low efficiency and the differences between topologies is very marked.

[anthonyTD]

The Beam Tetrodes or Kinkless Triodes where designed for audio from the outset IE low third harmonic and very low higher order harmonics (5th) all other valves where designed with something else in mind. I like the 300B, many of the SET guys don't but in a PP configuration they work well given a good cct like the original WAD 300B design...where many ccts fall down is in the driver stage, triodes have a lower input impedance and demand more from the driver stage IE large enough voltage swing. The design of the driver stage becomes more critical than the stage for the KT.

Also, the 300B power o/p is generally lower than that of the KT, the 300B grid would have to be driven positive to get any where near (this is where the likes of the 811 etc score as they are designed to be driven into class A2) and it's not really designed for that.

Another consideration is feedback, the 300B has a natural low output impedance without feedback and therefore its damping factor is relatively low, making it usable in zero feedback designs. Zero or low feedback makes for a very open and natural sound, many like this type of presentation.

The KT on the other hand can also be used without feedback but the o/p impedance is really too high like this so either local or global feedback is used to lower it. Adding feedback though alters the transfer characteristic of the amplifier and given a highly reactive 'speaker load the amplifier response can start to take on the same shape of the 'speaker...but feedback tightens the lower registers and narrows the sound stage, many prefer this type of presentation.

A mainly resistive and efficient 'speaker tends not to highlight these differences but use a high;y reactive 'speaker with low efficiency and the differences between topologies is very marked.

i agree,
this is why it is very important when using KT88's with low global feedback to use speakers with a very consistent impedence versus frequency characteristic, ie no serious dips or troughs in their impedence curves over as wide a frequency range as posible,[no over complicated cross-overs allowed to acomplish this either] or, as you have quite rightly pointed out, the amplifier will indeed be dictated to by the characteristics of the speaker load.
anthony,TD...

[Ali Tait]

I think the main reason some think 300b amps are poor is that it is a very difficult valve to drive properly.When this is done it's one of the best out there,as Steve said.I still remember his lovely vintage 300a's in Nick's amp at a previous fest.Sublime...

[anthonyTD]

I think the main reason some think 300b amps are poor is that it is a very difficult valve to drive properly.

When this is done it's one of the best out there,as Steve said.I still remember his lovely vintage 300a's in Nick's amp at a previous fest.Sublime...

agreed ali,
potential 300b amp users,repeat after me,YOU CANNOT DRIVE THE 300B WITH AN ECC83!!!

[Togil]

Mr. Park the Korean 300B designer also told me he thought the 845 usually had bad driver designs including the Nagra VPA

[Ali Tait]

The 845 is even harder to drive than the 300b!

[Dr. Flicker]

some of the worst SE amps i have heard have used the 300b,
and some of the best ones i've heard have used it too

Just goes to show you that people put far too much importance on the tube, as if a pair of WE 300B's will magically make every other inadequacy in the amp somehow disappear. Everything before and after it has so much effect on what the amp will sound like.

I've had two different models of 300B amps (from the same manufacturer), and the difference was night and day (the much better one was only marginally more expensive than the other one). Good design is key, and not easily accomplished, even by the most seasoned tube amp designers. There's simply too much voo doo alchemy in audio to guarantee a great sounding amp on paper.

Also, I think the 300B has such a cult reputation (not entirely undeserved mind you) and track record that it simply attracts fans because of it's "holy grail" status. They can also be stupidly expensive, and people do associate price with quality and desirability.

The 300B's do have one silly drawback (which doesn't bother me of course), but sort of seems like your getting short-changed in the "tubes are cool" game....they don't have much of a "glow" like most other tubes.

I am a current 300B fan though, and if you love that SET midrange magic, then the 300B will maximize the role of the tube in that regard very well. But the sound does not begin and end with the tube, and I would not hesitate to buy an amp with different tubes if the results were better.