Tetrode has two grids and
Penthode has three grids
If all grids are shorted than the bulb works the same as triode. If not than each grid can be used as an extra gain stage to amplify the voltage.
If grids have different polarity but the same offset DC voltage, they create a unity gain buffer i.e negative feedback. |
If your amp allows you to bias each tube separately then being matched is not important as long as they are reasonably close. If your amp biases them as pairs or quads then they should be matched. If you mix them up you must have a tube tester to sort them out again.
In general as you add electrodes (triode (3) to pentode (5)) you get more gain but most will say a colder sound.
Most audio power tubes are either triodes or pentodes. By connecting some of the pentode pins together you can make it act like a triode. |
KT88's often are described as clearer and more linear, pentodes like an EL34 or something, are often described as warmer or lusher. If you bought the amps new, you should have them replace the tubes. You shouldn't have to pay. If you don't have individual biasing for each socket, yes, check the manual. If it says in pairs then match. If not, don't bother. |
If you have mixed up your tubes, you will need a tube analyzer to pair them again. If you can bias tubes individually on your amp you need not have matched tubes.
The KT88 is a kinkless tetrode, i.e. the cathode and one of the grids are shorted. In spite of being called a tetrode, it has three grids like a pentode. Ditto for the 6550 tubes, which are known as a beam tetrode. EL34s are 'pure' pentodes. I have a couple of amps where I can use KT88s, 6550s or EL34s (and I guess a couple other tubes as well)
Depending on how the amplifier is wired, you can run the KT88 in triode, tetrode or ultra linear. You can run any the majority of tetrodes and pentodes in these three configurations. (There may be ones you cannot, I dont know)
Running a pentode/tetrode in triode mode normally gives a forward sounding midrange, but you pay a price as you restrict the output of the vacuum tube. Most folks seem to prefer this configuration. Ultra linear and tetrode mode allows the tube a higher output, but is not generally a preferred configuration.
To my ear a tetrode wired pentode/tetrode mode sounds the most dynamic and 'peppy'; consequently I prefer this layout. My all time favorite tube amp is a single ended tetrode wired 6550.
Run in single ended triode mode, I generally prefer the sound from EL34s.
In a push-pull configuration with so many tubes, you may as well stick to the KT88 as they have lots of oomph and given the configuration, will give more or less the same detail as any other tube.
Regards
Paul |
Let me put on my 1960's tube hat for a minute....
A triode has one grid, called the control grid. This is where signal is applied for amplification, and bias voltage is applied.
A tetrode has a second grid called the screen grid, between the control grid and the plate of the tube. It gets a positive bias (but no signal!) to cause more electrons to flow from the cathode to the plate, thus increasing current flow through the tube.
A pentode has a third grid, called the supressor grid, placed between the screen grid and the plate. When electrons hit the plate at high velocity they knock other elctrons loose from the metal, forming an electron cloud near the plate that can reduce current flow due to electron replulsion. The supressor grid is tied to the cathode and reflects these electrons back to the plate (they would normally be attracted to the positive charge on the screen grid). This improves efficiency.
If that's not enough there is another type of tube called a beam power electrode tube. Instead of a supressor grid it uses specially shaped metal electrodes to focus the electron stream onto the plate.
The 6L6/5881/KT66 is a beam power tube. The 6550/KT88, EL34 and EL84 are true pentodes.
As mentioned above you can use a tetrode, pentode. or beam power tube as a pseudo-triode by using only the control grid. If my memory is correct one normally ties the unused screen and suppressor grids to the plate. |
"What is the difference between Pantode and Tetrode tube?"
What is the difference between the analog forum and the amp forum? Maybe you should concentrate on THAT one first.......
Oz |
ya just gotta love the forum police |
Thanks Ozzy for pointing my mistake so eloquently. I am truly sorry if I have offended you.
I will attempt to post on the correct forums in the future.
Thanks to everyone else that offered there expertise and advise.
The Hurricane does have a switch on the top T and P it does not have anything in the Chinese manual about that switch I assume from the posts the that is Pantode or Tetrode, does that mean that the amp will run a tube in ether mode regardless of the type of tube or is it asking for the type of tube I am using.
If any Mod can move this to Amps Ozzy would be grateful.
Thanks |
Don't worry about the forum thing too much. If in fact you are looking for advice that's that technical let me add something about pushpull and triode v. ultralinear. B/c of the suppressor grid on the EL34, you could say that usually it sounds better in ultralinear and as someone stated, peppier. It has to do with that supressor grid, electron cloud, maximum plate voltage thing; you can probably see how. The get up to a plate voltage, max out, and output constantly at that level (no overdriving like on guitar amps, as far as I know; someone correct me if I'm wrong on this one, but it's what I've been led to understand). This is why you see EL34 amps that are *specifically* balanced designs in ultralinear more of the time than with octals like KT88's; it's about creating a really super standardized power envelope for ultra-reliable bandwidth and no power spikes or dips base on load. The KT88/66/6550's sound better in triode for the most part because you kind of rev the plate voltage up as high as you can in Class A, with no cut off; not real efficient, and can lead to clipping, but that's why they sound purer. If you have transformers that can handle it, you get the benefits of Class A and the extra bit of bandwidth from a single ended design. Single ended like RCA plug vs. balannced plugs, where with balanced all the interconnects are grounded. Not single ended like a single ended tube design vs. a pushpull design; two totally different things. I'm surprised how often I see that particular confusion even in reviews. I've said this on another forum, but I'll say it here too: it's the difference between the sound of Sun Studios say (the EL34 camp) and like a great Verve recording (the KT88 camp), though not maybe as clear cut as rock vs. jazz. |
The Hurricane does have a switch on the top T and P it does not have anything in the Chinese manual about that switch I assume from the posts the that is Pantode or Tetrode What you are likely referring to--someone correct me if I'm mistaken--is the option to switch between Pentode or Triode mode. When running in pentode, your monoblocks will put out more wattage (200W), giving the music more punch and drive. To my ear, pentode is a bit more closed off in the midrange than triode (T on your amp) mode, which will lower the wattage (90w), but the sound is generally warmer and sweeter. If you are switching between the two, my understanding is that your amps require powering OFF before doing so. I hope that answers your question. If you want a more technical explanation, I'd suggest searching the Web. |
Thanks
I am still a little confused about tube matching the Hurricane allows for each tube to be biased independently in this case is a matched pair still important.
In addition, I was going to buy a tube tester and had asked on THE AMP FORUM about which one would accommodate the KT88s and EL34s (for future experimentation).
One reply was that a small portable one would suffice but it would not "computer match" the tubes.
What makes a matched pair? |
Punk--
1. When output tubes can be biased separately, 'matched' tubes are NOT required for excellent performance.
2. Are you sure your 'Canes can use '34s? I don't recall seeing that in my manual.
3. You do NOT need a tubetester. The WORST thing that will happen is one tube you install will be shorted or will arc and blow the high-Voltage fuse. (You DO have spare fuses--both kinds--don't you?)
4. Heed the instructions when replacing output tubes--the bias pot for that tube should be turned full down...CLOCKWISE, not counterclockwise...before you turn the amp back on. Turn the bias-selector switch to that tube, turn the bias meter on, and then adjust that tube's bias after the high-Voltage relay closes and the bias amount sort of settles. You probably already know that the tubes' bias draws vary considerably from cold to hot; if I've not moved my amp(s), I adjust mine before I turn the amps off for the evening.
5. 'Matched' output tubes are very close in bias draw, so that they'll work correctly in amps without separate bias adustments per tube.
Enjoy your 'Canes; I sure enjoy mine. I just finished my improvements; see my system.
Do you use yours in UL or triode? What do you drive with them?
PS. It's 'pentode'.
. |
I am waiting on a pair of Merlin's as for the P/T I have only tested the amps with a Gallo Due to check if they are working.
The Merlin's should be here in about two or Three weeks I may well sell the Hurricanes and get a pair of Manly Snappers Bobby at Merlin said it is a great amp to drive his speakers.
As for the EL34 you are correct the Hurricane does not use them but if I do change amps for something smaller it will have the 34s.
I just won a Superior Instruments Co. TD-55 Tube Tester on ebay and hope it will accommodate my tubes as I found it difficult to find answers to which tube tester works with the KT88s I have a sinking feeling that this one does not.
There is a B&K CRT 465 coming up on ebay can anyone can tell me if this will test KT88s or if the TD-55 will work with 88s 34s and the other ones (That I cannot remember the name of) |
Actually if you have an old mom & pop style radio shack place or seriously old school drug store, you may be able to find a tube tester locally - I happen to have a place like that around, and just like back in the 40's and '50's you can take your tubes in and get a reading by plugging them in to various sockets, turning a dial then pressing a button. I think computer match means "pay us extra for the same service; it will be on a computer plugged-in tube tester". Basically the difference between matched an unmatched is tubes used in tandem, or each tube on its own. Different topolgies is all. Personally I don't see one as inherently better than the other. Hurricanes and Merlins should sound great. If you get bored and want a sweeter sound, you can always try the EL34's. Merlins tend to be sweet. Should be a good balanced match with the KT88's. |
