I'm building up my KT120/KT88 amp right now. I have already had this running with KT88's and it really did sound nice. I found the KT120's and had to try them and also wanted to upgrade the power transformer to something a little beefier. I will be able to switch back and forth between the KT120's and the KT88's so I can do a "shoot out". I have visual analyzer working so I can measure distortion now, where I couldn't when I first built this as a KT88. Maybe it will have terrible results for both tubes I do not know. Ah, this is what makes this hobby fun!
Oh this will be all triode with no multistage negative feedback. PSU II calculates about 470v B+
Oh this will be all triode with no multistage negative feedback. PSU II calculates about 470v B+
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Mel
I like the design of your amp very much..Couple suggestions you may want to try..Change the 12au7 to a 6cg7.Your distortion product will fall by 30 to 40% at plate of the 6cg7..Also,the .68 k40y or the Russian kBG paper in oil caps there are superb in that position.You can also add 35uf@500v or a 100@600v poly filter caps..All these things will make phenomenal improvements.
No,He needs 600v caps..That was a typo on my part..He can use motoruns that are rated 370vac which are good to 745dc before they start to breakdown
Hi Melb
The circuit you are using is very marginal to drive triode connected KT88's or KT120's
This circuit would drive pentode connected KT88's but only just; you need an extra stage.
Also look up the data for the KT120 the max grid resistor with Fixed bias is only 50K not 100K; that's if you want your tubes to last. You need to add a push pull driver stage. changing to a 6cg7 will not make any difference, but you could use 6CG7's as the push pull drivers, much better sounding than12AU7's
Your circuit of course will work and will sound very nice, but no dynamics; it will sound like a SE 300b amp driven by 12Ax7's.
The circuit with the 5687 can drive cathode connected 6550's so will easily drive triode; the best circuit would be the one with Russian 6N6's.
best to only drive class A if direct from the phase splitter.
Phil
Phil
The circuit you are using is very marginal to drive triode connected KT88's or KT120's
This circuit would drive pentode connected KT88's but only just; you need an extra stage.
Also look up the data for the KT120 the max grid resistor with Fixed bias is only 50K not 100K; that's if you want your tubes to last. You need to add a push pull driver stage. changing to a 6cg7 will not make any difference, but you could use 6CG7's as the push pull drivers, much better sounding than12AU7's
Your circuit of course will work and will sound very nice, but no dynamics; it will sound like a SE 300b amp driven by 12Ax7's.
The circuit with the 5687 can drive cathode connected 6550's so will easily drive triode; the best circuit would be the one with Russian 6N6's.
best to only drive class A if direct from the phase splitter.
Phil
Phil
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Hi Speakerfritz:
I get 470v as does Multi with a 200mA load. The DC resistance of the 356v tap is 22 ohms and using 1N4007 diode bridge in PSU II gives 470v.
Phil: Your second circuit gives you ~4.9 mA of drive current. My circuit gives 4.2mA of drive current. Will there be that much difference?? I am going to stick with the 100k grid resistors as my bias is individually adjustable. If I were slamming them into a guitar amp where you need "matching" pairs then ya better be at 50K there.
Michaelsamra: I have tried "oil" caps and really don't like them. I will stick with MKP types for coupling caps. I may look into some poly filter caps for sure!
What's with this magical 6CG7? I found a couple on Ebay for cheap so I will try them.
I have warned Bob a number of times about the high risk of using KT-120s with the Cit II heater windings. They don't have the reserve to handle an added 1.2 AMPS of heater current - at least not for long. I strongly recommend that KT-120s NOT be used in Citations.
My tech and I have both had the "pleasure" of doing repairs to some of the Carver modded amps.
As an Irishman I can tell you that while I like Bob and enjoy talking to him, he does have a "touch of the blarney" in him.
It sort of reminds you of that crazy stubborn hardheaded Lebanese you know in Michigan.Argh argh argh! Just had to throw that in Jim.
It still can't be denied that they give a HUGE performance improvement to the Citation II. The change is usually accompanied with a change from selenium rectifier to silicone, and much larger filter caps. If you put in a slow-start current-inrush limiter and lower the main fuse rating they seem to live OK. If the heater current was a real concern to you, add another small $15 transformer for the first small tubes. What a wonderful way to add performance for such low cost.
I would love to know what people are hearing that is so wonderful sonically,that people are hearing with the KT120s..The curves are atrocious,and in a citation 2,you are working outside the original design parameters.
The only advantage I can see is more power,but that won't happen with a mere subbing of a kt120 and adding a filament transformer.You still need more drive and more B+ for the tube to produce its potential.
This is like putting heads with bigger valves and higher compression pistons on your small block Chevy or Ford engine to make more horsepower and then you leave the same size carburetor or fuel injectors and throttle body on the engine..That isn't going to do a dam thing because you are starving the fuel and air supply for the new components to be effective..In the case of the Citation and the Kt120s,you are starving the B+ and signal supply to make that tube run at its potential.
It's NOT the KT120 that's making things better. It's replacing dried out, 50+ year old, PSU 'lytics with the vastly superior parts currently available, along with swapping nasty, noisy, unreliable, old SS rectifiers out, that yield the substantial, audible, improvement. Jim McShane has been doing exactly that, for approx. 20 years!
Jim also installs an improved grounding setup. BTW, THE O/P tube to install install in "Deuces" is the EI KT90, either type 2 or early production type 3. Sadly, those "puppies" have become scarce NOS items. Given the current situation, the "reissue" Gold Lion KT88 is the "proper" choice, when retubing a Cit. 2.
Beefing up the power supply's ability to handle a powerful transient isn't going to help much when the KT88s are the limiting factor, but with KT120s you can realize real benefits. Like I said before, you don't need to raise the B+ voltage as their main advantage is in delivery of more current, though they can also handle additional voltage. It's more important to lower the load impedance than raise the B+, but the power is the limit. You can do fine by lowering the impedance of the load (or using the "wrong" tap) and get a LOT more current and a LOT lower and louder bass, and with those wonderful transformers in the citation you don't lose the high end. Look around on the internet and ONLY this DIYAUDIO website has focused myopically on one set of curves without comparison curves from KT88 and KT90 done on the same setup. The KT120 curves you're looking at probably had a resonant load and the KT88 curves you are used to seeing are probably averaged. They're intended to have utility function in deciding how to use the tubes. The lemmings on here as so used to repeating the rumors they believe them, instead of either making comparison curves or listening. I haven't been convinced that they really have a problem that isn't really a fault in the test setup.
Yes, Carver is a real character, but he knows what he's doing with the Citation II conversions; I think he also converts them to not be ultralinear any more. Amazingly, I hear Carver got that from hegeman himself. The KT120 and those high-quality transformers sure seem to work together much better than with KT88s. Each KT120, without raising B+, is like a KT88 and a half. It's adding plate area in parallel. Those "bad" curves have utility for deciding how to run them, but their cyclical ripples more indicative of the load and supply, resonances in the test rig.
If anyone has better quality data, I'm eager to listen, as there's still not much good enough comparison data on them this many years into production. I'm obviously not going to get anywhere asking some people to keep an open mind; but if you are open to it I encourage you to check them out yourself. I could even be wrong. Time will tell. What I do see is a clear division, with the whole world having one opinion and DIYAUDIO having another opposed view because they keep referring to one set of curves and repeating the same thing to each other. Just keep an open mind. And the heck if I want to spend twice to three times the money on tubes with half less power. I'd take 6550s over a KT88s. But the KT120 is better and cheaper. IMHO it makes a Citation II with beefed-up power supply a lot better balanced amp with a lot more powerful and lower bass, instead of such an overbuilt low-power amp.
Yes, Carver is a real character, but he knows what he's doing with the Citation II conversions; I think he also converts them to not be ultralinear any more. Amazingly, I hear Carver got that from hegeman himself. The KT120 and those high-quality transformers sure seem to work together much better than with KT88s. Each KT120, without raising B+, is like a KT88 and a half. It's adding plate area in parallel. Those "bad" curves have utility for deciding how to run them, but their cyclical ripples more indicative of the load and supply, resonances in the test rig.
If anyone has better quality data, I'm eager to listen, as there's still not much good enough comparison data on them this many years into production. I'm obviously not going to get anywhere asking some people to keep an open mind; but if you are open to it I encourage you to check them out yourself. I could even be wrong. Time will tell. What I do see is a clear division, with the whole world having one opinion and DIYAUDIO having another opposed view because they keep referring to one set of curves and repeating the same thing to each other. Just keep an open mind. And the heck if I want to spend twice to three times the money on tubes with half less power. I'd take 6550s over a KT88s. But the KT120 is better and cheaper. IMHO it makes a Citation II with beefed-up power supply a lot better balanced amp with a lot more powerful and lower bass, instead of such an overbuilt low-power amp.
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Excellent point.
I have been in audio for a long time and I remember reading the what the so called critics had to say back in the 70s,and 80,and 90s,until now..Once I became very proficient at rebuilding and modifying and making design changes to gear,it made me realize that the people telling us how good they think an amp or preamp is,are nothing more than people who listen to different pieces of equipment and have an opinion.What makes them any more qualified than the rest of us?
The blatant truth of the matter is this..The only reviewers I found to be spot on was consumers reports..If you pick up Consumers Reports magazines of the 60s,they rated everything from Sherwood to Mac.They used to brag about how wonderful the Sherwood midrange was as well as the wonderful bass in the AR3s.Those are just two examples but they weren't bought off like reviewers in other audiophile publications.
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