Anyone know how to bias output tubes (using built in meter) on a Stereo Knight M-40 (Int. Amp)?

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