Single Ended Triode vs Pentode

[HighFidelityGuy]

I've not seen much discussed on the comparison between single ended triode and pentode amps and I'm interested to hear peoples opinions. Triodes seem to be treated with much reverence, while pentodes seem to be a little looked down on in comparison. What's the reason for this? Do all triodes and pentodes share a similar "sonic signature" in their respective families and how would you describe the differences in the sound?

Thanks.

[SPS]

That's really a can of worms...
so with out trying to get technical.. which i'm not very...

i assume your wanting to compare single ended triodes to single ended pentodes..

they can be very close in my experences, the quality of the output transformers/ valves and components are critical with any valve amplifier

the main advantage is that feed back is not required with the triode amp,
which many feel can give a more pure sound.. but at the expense of less watts output

pentode amps tend to be less load tolerant.. so feedback helps in this deptment and is esential for the amp to be reasonably accurate through the frequency range with varing loads typical of many loudspeakers

generally global feed back is used on all amps with feed back. some of the signal on the loud speaker output is put back into the input of the amp.. feedback has many advantages and many believe some disadvantages...

there are followers of all types of amps, i found going from a couple of single ended pentode amps ( with el34 and el84 valves, 9 watts and 4 watts) to directly heated single ended triodes ( px4) found quite a sonic improvement in the level of bass, and the amount of detail produced...

hope thats some use...


cheers steve

[Ali Tait]

Well VERY generally-Single ended triodes are the most linear amplifying device ever made by man.Their strengths are in the fantastic realism they can impart,especially to the midrange and top,unbeatable if done right IMO.They can be perceived as being weaker and more wooly in the bass than a pentode,but I think this more often than not is down to poor implementation and/or too inefficient speakers.Triodes can do bass as well as anything,it just takes more effort to get right.

A pentode PP amp by contrast,will have a muscular sound,with a better grip on the bass on normal commercial speakers.A PP amp will have more power output,so will work well with a much wider range of commercial speakers.Won't have the magic mids and tops of the triode though.Nothing else does.

Both can sound very good,but I think to hear each at their best,unless you've won the lotto,diy is the way to go.I will say though,it's quite difficult to build a really poor valve amp,to my ears even a mediocre valve amp sounds better than most solid state.

Just MHO!

[Dave Hewitt]

Hi
I think Ali's pentode 813 amp connected as a triode was quite superb,sounded good to me,so who knows.
Dave.

[anthonyTD]

of course other reasons for choosing triodes over pentodes/tetrodes and vice versa is distortion characteristics,and power output. triodes produce mainly even order harmonics which are much easier on the ear and thus more attractive to the pureists who frown on the use of any type of feedback, pentodes/tetrodes produce even and odd order harmonics in single ended configuration, feedback can be used to lower over-all distortion in both triode and pentode configuration, although it is seen to be more of a nescesity in pentodes/tetrodes than triodes due again to the type of distortion produced.
if you can reduce the amount of odd order harmonics in pentode/tetrode configuration to an acceptable level then the advantage of higher power outputs and thus higher efficiencies from the pentode/tetrode can be realised.
A...

[slipperyjim]

As Ali stated the triode Ia/Vg curve is far more linear than the pentode's. Because of this, it is possible to build amplification, even power amplification, stages requiring litlle or no negative feedback to linearise the characteristic.

Feedback is looked down upon in many quarters for the potential problems it can introduce, the chief being transient intermodulation distortion (TID) where, if any part of the loop goes non-linear then the feedback increases the distortion rather than decreases it. Demonstrate this with guitar amps where Marshalls have more feedback than Fenders of the same architecture (e.g. tweed bassmen) and get a dirtier sound. There are other effects which have been quoted such as blocking which I thought I once understood.

There is a point of view, though, which states that the screen grid and suppressor grid in tetrodes and pentodes actually defeat local negative feedback loops which are inherent to the triode via space charge, Miller effect and secondary electron effects. Therefore the evil negative feedback is always present anyway.

All I know is that I once owned a Pye Mozart single ended Pentode amp (EL34s) with a hideously complex triple feedback loop trying to keep the thing under control. The worst sounding thing I've ever heard (and I speak as someone who once inadvertently heard Coldplay). Looked pretty though, pink chrome. Sold it for a small fortune to a far eastern "enthusiast".

[HighFidelityGuy]

Thanks for the replies. So it sounds like triodes or an advanced implementation of pentode/tetrode can produce the purest sound with the latter having the benefit of higher output but with a more complicated design. So triodes are the simplest and purest design but can lack some power and bass authority. That tallies with what I've read elsewhere so that's good.

This seems like a good place to bring the Icon Audio Stereo 20 SE into the discussion. This promises to deliver the fabled triode sound with all of the benefits and none of the negatives and for a surprising low price of £999. It even has a high (for SET amps) output of 20W RMS per channel. So this sounds like the perfect SET amp. It seems too good to be true but I know Icon has an excellent reputation. Can anyone comment on this and more importantly has anyone heard it in action?

Cheers.

[goraman]

a pentrode can also be be wired to ultra linear,My amp is switchable from triode at 20 watts to UL at 40.It stays in triode 90% of the time but 10% of the time I'm playing hard hitting rock. Triode is very atherial and detailed with huge sound stage and unreal space between insterments.UL has far more deep thump but is still more defined than a normal pentode push pull. Then there is single ended triode amps,great for jazz and some blues but horrable for Rock.

[SPS]

Then there is single ended triode amps,great for jazz and some blues but horrable for Rock.

many are.. but not all...its all about speaker matching and the quality of the amp in my view... i would say a 'good' se triode can do everything very well

my 3 or 4 watts plays led zep, massive attack and the likes..
with real quality...

but.. if it was not matched with suitable speakers....your right...it could be horrable ...

thats really what hi fi is about... matching

cheers
steve

[SPS]

Thanks for the replies. So it sounds like triodes or an advanced implementation of pentode/tetrode can produce the purest sound with the latter having the benefit of higher output but with a more complicated design. So triodes are the simplest and purest design but can lack some power and bass authority. That tallies with what I've read elsewhere so that's good.

This seems like a good place to bring the Icon Audio Stereo 20 SE into the discussion. This promises to deliver the fabled triode sound with all of the benefits and none of the negatives and for a surprising low price of £999. It even has a high (for SET amps) output of 20W RMS per channel. So this sounds like the perfect SET amp. It seems too good to be true but I know Icon has an excellent reputation. Can anyone comment on this and more importantly has anyone heard it in action?

Cheers.

the link refers to the triode class a front end.. which i would guess is the driver valve... and not the kt88 ?

i would guess its very nice sounding amp.. but i've not heard it

best way is to get your kit in your car and spend a bit of petrol money first.. listen to others kit next to your own.. you would learn far more about valve amps with little cost.. you would know how many watts you really needed and how your speakers compare, and find out which valve amps actually do bass... and that sweet mid range.. and if it would be worthwhile or wasted with your present speakers..

most valve amp users eventually go for high(er) eff speakers... usually for good reason..

I'm nr the humber bridge .. your more than welcome to come and see what my valve amps do well. and if they are to your tastes.
cheers
steve