Google turns up ZERO info on Stereo Knight M40 Tube Amplifier.Are there any visible Bias Pot openings on the top plate near the power tubes?Are you sure the meter is for tube biasing?It seems to me if they provided a meter biasing pots should be easy to get to.If nothing is visible your going to have to open the bottom plate & have a look around.WARNING,there are capacitors inside that will store enough voltage to stop your heart in a,well heartbeat,ONLY DO THIS UNPLUGGED & AFTER A FEW HOURS SO CAPS CAN DRAIN.If you don’t like doing this you’re going to have to take it to an ece.tech.
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Thanks freediver for responding. There are tweaks next to each tube (4), and there's a switch on the side to select 1 thru 4 (tubes, I'm assuming), it's currently setting on 4. Then, there's a removable plate, next to the 1-4 switch, behind it has four RCA connectors, labeled 1-4. That's what I got. The meter is definitely for biasing, it's inside the cage, and calibrated in mA, 0-100 mA. So the switch surely connects the meter to each tube, but I don't know what to do with the RCAs. I've measured them. with power off. Grounds are ground, and the plus lead reads 10.3 ohms. Kinda sounds like a cathode biasing resistor? But who knows? This is a ZERO feedback amp, and it sounds unbelievable. It set new standards for me, and made most of my other amps crappy in comparison. Gotta keep it running!!! Let me know if you can help. |
Thanks Peter, good idea. Here's a url with photo's and detailed description - except how to bias. http://www.stereoknight.com/S-40.html |
Sounds like the meter acts as test point.Disregard RCA's for now.They shouldn't have anything to do with biasing.Try setting switch to #1,then slowly turn tweak(your word)next to tubes & see if meter changes.NOTE setting before moving tweak so it can go back.Pics in your link don't work.Maybe you could post pics in a virtual system so we can see it. |
Thanks freediver. FYI - I'm a bit of an idiot, the amp is an S-40, not an M-40, sorry for any confusion. I've set the switch to each number (1-4), with the amp on (its an integrated), with no inputs, and volume set to 0, the meter always reads 0. I also tried turning the pots (tweaks) next to each tube, but the meter doesn't move. I'm thinking the RCAs are used to "insert" the meter's "other lead", with the 1-4 switch being one, and the RCA's being the other. If it's a true current reading, it'll need to be in series with the cathode, somehow they have to "break and insert" the meter in series. Perhaps the switch is set to 1 and RCA #1 is shorted? |
Ok,Google turned up just enough info.I believe the 4 RCA's are so the passive preamp section can be isolated from the amp should you choose to use a different one.I think the problem is you must have a load on the amp to Bias.The single slot adjustment screws next to each power tube & the 1-4 switch should work together.First thing I would do is hook everything up & see if you get any sound.If your getting sound & the meter doesn't register it may be broken.Once you've confirmed the amp does work try the switch & bias pots,see what happens.Beautiful amp by the way.Good luck. |
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I wanted to elaborate on my findings re:the 4 RCA's on the side.First I am only about 70% sure that the info I found also applies to the S40 as it comes from the S.N.stand alone Reference PreAmp,which is the foundation of the PreAmp in the S40.Apparently when used as an Integrated Amp the S40 has an Active Class A PreAmp Stage.If I'm right the 4 RCA's are in to the Passive Stage of the PreAmp & out with just enough gain to drive the reference monoblocks they offered.Once you get the amp running you can test this theory. |
Hi Freediver. A little reset here. The amp works great. The sound is absolutely amazing. I have several tube amps, but none with NO negative feedback...this thing really sings...it's ...in my world..unbelievable. BUT...I don't know how to get the meter to engage. The RCA's are not preamp out - power amp in. They are four RCA's with open connectors. No shorting straps. They are part of the biasing scheme, could be a short when applied, or maybe some resistance??? I believe the amp must of had some biasing fixture that plugged on the appropriate RCA of the tube you are biasing. I did do all the testing of the 1-4 switch, with the amp under load, but no input, and volume at 0. The S40 is an active preamp (class A) feeding their KT88 tube output in what they call class A push-pull. (???) In my world, all push-pull is class AB by definition, but???? I can't argue with the sound of this amp. Just need to know how to keep it working. I may have to buy a KT88 biasing socket. |
Hi. I realize this thread is about 7 years, but it’s very relevant to me as I’ve just got the same amp (StereoKnight Lancelot S40) Just as the thread starter, I’m not able to find any information about this integrated amp. Would really like to know a bit more about it, and also info conserning the bias system So therefore I respond to this old thread. Hope someone has some info about it (What a beauty of an amp this is 😊) |
Congrats aasbakk, you have found a great amp. I didn't know anything about StereoKnight or the S40 when I got mine, but after having it for a decade, and having bought several other amps, I do know now, how special this amp is (still have it, probably never let it go). Sooo... I did some digging to find out how to bias it. I discovered one of the two StereoKnight principles (the tech guy), started another audio company in Australia, and I was able to find out from him how to set the bias. You do use the four RCA connectors that are behind the little square panel on the left side of amp. Each RCA connector correspond to an output tube. The RCA connector is used with an external voltmeter. RCA + connects to meter +, RCA - connects to meter -. (Note: the built-in amp meter does not work on the S40 - it's not even wired - I looked.) Basically, the RCA connector lets you connect a voltmeter across a 10 ohm (cathode resistor). The bias specification is 45ma, so 45ma across the 10 ohm resistor produces 450mV. This is what you'll read on the meter, 450mV or .45 volts. So the bias steps are; 1) Hook up voltmeter to RCA connector #1 (to bias tube #1 - tube furthest right) 2) Turn on amp with no input signal, volume at 0. Let tubes warm up for 5 minutes, and take measurement on meter. If not 450mV, use the tweak (potentiometer) next to tube #1, and set the voltage to 450mv. 3) Turn off amp and move voltmeter to RCA #2, and repeat. That does it. Hope you enjoy your amp as much as I've enjoyed mine. I'm currently running a set of Gold Lion KT88, NOS Mullard E188CC, and NOS Amprex 7316. Man-o-man does this thing sing! (FYI - Good NOS tubes in the front end really made a difference.) |
Thank you very much 😀 I really appreciate your help 😀 i god this amp in replacement for my Rogue eighty-eight, and man did those speakers come to life. The sweetness an dynamics are superb 😀 I run a pair of Audio Physic Virgo 1. Source is Roon server with Qobuz for digital, and a heavily customized Lenco L75 for analog very happy with my setup, and I’ll try biasing later this week btw. Do you know any technical specs for the S40?, and if there buildt riaa (I suspect there is only the name of the input, and not a built-in?) Again. Thank you very much for your response. It’s quite enjoyable being the owner of such a wonderful, and rare amp 😀 all the best Jon Anders |
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