You got it SY..I mostly use the sq wave for setting up feedback bypass capacitance...You look at the Sq wave and you find ringing or peaks and then bypass with a certain value to get rid of the ringing..As you said,the sq wave doesn't have tons of value other than to show that the amp working properly but you can't really determine that much from it other a pretty signal..
Minuscule refers to small as in lower-case type. Miniscule is more correct.
Where there were KT88, 6550, KT90...using KT120 now and I'm not looking back.
Where there were KT88, 6550, KT90...using KT120 now and I'm not looking back.
Do you like the KT120s? I hear a lot of good things about them..Are they as good sonically as a kt88?
Mikey,
Get a hold of the KT120 plate curves from you know who. They are downright FUGLY!
I can't fathom why people are making such a fuss. Besides being non-linear, the type draws a lot of heater current and has a very low grid to ground resistance limit.
JMO, the KT120 is a guitar amp tube. You have to bludgeon it with a lot of NFB, to use it for music playback.
There is a popular falsehood circulating that installing KT120s into KT88 sockets "automagically" increases an amp's power O/P. 😡 The FOOLS who buy into that utter nonsense are lucky they don't "fry" their power transformers.
Get a hold of the KT120 plate curves from you know who. They are downright FUGLY!
I can't fathom why people are making such a fuss. Besides being non-linear, the type draws a lot of heater current and has a very low grid to ground resistance limit.
JMO, the KT120 is a guitar amp tube. You have to bludgeon it with a lot of NFB, to use it for music playback.
There is a popular falsehood circulating that installing KT120s into KT88 sockets "automagically" increases an amp's power O/P. 😡 The FOOLS who buy into that utter nonsense are lucky they don't "fry" their power transformers.
There is a popular falsehood circulating that installing KT120s into KT88 sockets "automagically" increases an amp's power O/P. The FOOLS who buy into that utter nonsense are lucky they don't "fry" their power transformers."
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Exactly Eli..They don't realize that ohms law still applies.They have to proportionally increase the plate voltage on the 120s and the driver to effectively have the tube produce its rated power.
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Exactly Eli..They don't realize that ohms law still applies.They have to proportionally increase the plate voltage on the 120s and the driver to effectively have the tube produce its rated power.
As I said, that's a very, very, nasty looking set of curves. 🙁
Methinks the "Emperor's New Clothes Virus" is running rampant, yet again.
Methinks the "Emperor's New Clothes Virus" is running rampant, yet again.
Sorry, from the Latin minuscula is what I should have written. Miniscule is just really a mishearing of minuscule and an association with all the "mini-" words we have.
Spoken like someone with a big personal investment in competing tubes versus someone with a big personal investment in KT120s. Yes, I got 8 for a bass guitar amp project. Think of a long-plate KT120 as a KT88 and a half in parallel; you only have to raise the B+ voltage if your regulation is so poor that's the only way you can deliver more current or it's originally lowered to accomodate the poorer power dissipation limit of the KT88; a much better approach is to drive a more difficult load with the KT120; just use a different speaker tap. Don't just invoke Ohm's law, apply it properly. You're adding plate area in parallel; if you were adding output tubes in parallel would you mostly increase plate voltage or mostly decrease load impedance? I'm actually surprised there have been very few reports of damaged power transformers; I guess it shows they're generally better protected and more overbuilt than we give them credit for, and the typical reported improvements in bass probably shows how banks of big caps pay off in newer designs using them as a power reservoir versus older designs from before such caps were available economically which used to implement the minimum required for filtering hum. Whether you actually get more continuous power out, or "just" much better dynamic range and bass on transients, or "just" much longer tube life depends on how old-fashioned (and crappy) the power supply design is, how generally bad (cheap) the amp is (especially the output transformer), and whether (and how) the KT88s were previously limiting performance. The capacitances are more, (especially with miller effect I guess??)...so they only go into lower RF LOL. Runnning cooler, they stay matched much better than lesser tubes running nearer their limits. The longer plates have longer heaters, but even that's efficient compared to the output. Less cost, space, and complexity if you can use 8 per channel instead of 12.
I haven't seen curves I really trust yet, taken on the same setup at the same test session, with both the KT120 and KT88. They curves look more like a problem in the test setup to me, but I'm no expert. They sound great in the new Conrad Johnson amps. Online, reports from users are favorable to unfavorable about 1000 to 1, with only DIYAUDIO.com fixated on curves of questionable origin and yes-men jumping on the bandwagon of criticism. The vendor does us a disservice by not providing more and better specs, but does us a service with a consistent stable product with specs that don't drift quickly with age...for a change. I'm a believer, but not quite religous about it; still too early.
I haven't seen curves I really trust yet, taken on the same setup at the same test session, with both the KT120 and KT88. They curves look more like a problem in the test setup to me, but I'm no expert. They sound great in the new Conrad Johnson amps. Online, reports from users are favorable to unfavorable about 1000 to 1, with only DIYAUDIO.com fixated on curves of questionable origin and yes-men jumping on the bandwagon of criticism. The vendor does us a disservice by not providing more and better specs, but does us a service with a consistent stable product with specs that don't drift quickly with age...for a change. I'm a believer, but not quite religous about it; still too early.
It's a British English versus American English difference in whose dictionary you subscribe to. So I'll let the subject die; you have more history on your side.
Very low grid to ground resistance limit of the KT120. looking at the data for the 6550 it too has 50K limit for fixed bias. Nos KT88's specified 100k, but i noticed on some of their amps they reduced it to 68K, and the design for a 8 X kT88 amp uses 38K. Current production Kt88's can they handle a higher resistance to ground, than 50K? I doubt it. I still see lots of amps designed for 100K for both KT88's and 6550's.
How important is it to keep to the data 50k for the 6550's, Kt120's, Kt88's.?
I have seen circuits for the Jadis using 1 meg on the grid of a fixed bias x 8 6550's: no wonder they blow up.
Phil
How important is it to keep to the data 50k for the 6550's, Kt120's, Kt88's.?
I have seen circuits for the Jadis using 1 meg on the grid of a fixed bias x 8 6550's: no wonder they blow up.
Phil
That's not true either. Most American dictionaries (online, at least) acknowledge that "miniscule" is a mis-spelling.
Guess again! 😉 I possess 2 sets of EI KT90 Type III and an old set of Chinese KT88s and that's it in the big beam power tetrode dept. The KT88s came with my "Deuce", when I acquired it, and the KT90s were acquired as part of the refurb. project. I lack both the space and the cash to make a large investment in any specific tube type. I'm a hobby enthusiast, not a dealer.
I took 1 look at that curve set and said, YUCK!
Many other curves you see are somewhat averaged, intended to be of useful utility for design rather than accuracy for evaluating the tube. For all I know maybe the sweep wasn't smooth or the load was resonant.
And now that you bring price into it the KT120 becomes much more attractive, in dollars per watt per hour. You get more power for a comparable price in a device with a longer life.
In a bass guitar amp that gets thrown around I don't know for sure whether longer plate and grid distances between supports is risky, but my application only fits 8 output devices, and it gets difficult to package the 12 that Mesa puts in some of their bass amps. Some claim that it's more important that the plates and grids not get overheated.
Hi Eli,
Just a quick question regarding the KT120 tubes -- can they be used as a drop in replacement for the KT88 tubes?
Some sites tout it not as more power, but more headroom where you won't run into distortion at maximum levels that an amp designed for a KT88 amp. i.e. KT88 SE amp outputting 15 watts at maximum, drop in KT120 in there and you won't experience the distortion levels when you turn it to max. This gives you longer tube life, reliability, and impervious to overload in a circuit designed for a 6550/KT88 circuit. Some sites say it is because of the larger construction and more rugged design.
As I said, that's a very, very, nasty looking set of curves. 🙁
Methinks the "Emperor's New Clothes Virus" is running rampant, yet again.
You ainta kidding that's a shitty set of curves..Why would they market a tube like that? At the very least,they should improve its power bandwidth and overall frequency response because that tube in most circuits will need a lot of feedback to be stable at higher power which is why you would use the KT120 in the first place.
Absolutely not! The KT120's heater current draw is greater than the draw of a KT88. If the power trafo's filament winding(s) are sized just large enough, but without a reserve, overheating will occur and failure is a distinct possibility. Unless an amp's builder explicitly states it's safe, installing KT120s in KT88 sockets is FOOLHARDY.
Also, Mr. Samra previously explained that operating condition changes are necessary to get greater power O/P. P=I2R=EI=V2/R. Unless the voltage swing in the load increases, the power delivered doesn't change. The fact that the KT120 may be able to swing more voltage does not mean it will, when it's installed in a situation engineered for a different type.
The claims are bogus! The Laws of Physics do not yield to the whims and wishful thinking of humans. If you want the power O/P KT120s are capable of delivering, the circuitry used must be designed, from the ground up, with type's character in mind. I suspect that includes using O/P "iron" with smaller step down ratios than the ratios used with KT88s. Increased magnetic headroom in the O/P "iron" is a given. TANSTAAFL holds true, again.
The plate curves say, to me, that the KT120 is a POS, for HIFI purposes. The graph doesn't lie. The KT120 is highly non-linear. CJ , ARC, and anybody else are welcome to use the KT120 and turn substantial profits. I'm not in the hobby to make a living. I will not design for the type, as guitar amps are not my "thing". L_RD knows, KT120s are not going into my "Deuce".
To make money! Perhaps this video should be required viewing for all sorts of folks, especially audio enthusiasts. 😉
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