kevin gilmore

I think that those things are going to perform very poorly at 20 ma, but i'm willing to give it a try. Gate capacitance not too bad. Now to find someone with the things in stock. Would be neat to run the things at 100ma, but you will need a fork lift to move the required power supply... Figure about 800 watts with the current sources.

Don't forget the one diode on the power supply board that is backwards, 4 of the diodes, one on each of the supplies is actually a zener and the resistor cross for the servo. also if you get a universal primary transformer, don't wire both the 110vac and 220 vac lines...

solid state front end is definitely doable. Cut the +250 to +100, use 2sa1486 as cascode transistor, cut R6 in half and use everyone's favorite n-channel front end fets. Add zener at junction of R9 and R10. change out the fet and led's in the batteries for the precision regulator and a resistor, remove one adjustment. might have to fiddle a bit with the range on RV1. Neither should make any change in the sound whatsoever. But its not better. There is no suitable 1kv + transistor to replace the output tube. But if anyone knows of anything suitable please let me know. Something that can handle at least 20 watts with 500 volts across it. Cathode of output stage with tubes is possible but then the -500 would have to be -600 or more, then remove Q26,27,28,29 this would likely change the sound a bit. All the output current would have to go thru this tube, and thats a bit much for the kind of tube you would need to use. Still nothing really stands out as any better. Just maybe a slight bit simpler. If you think this thing gets hot, you should have touched the original. No practical way to replace the active batteries with a tube. Gas tubes have too high an impedance.

This is a way better way to explain the tendency to crank the volume. No fatigue of any kind, even at ear bleeding levels. And i can listen for many hours at levels way louder than i should. I've been thinking quite a while on this, what i would do to make anything that would be better than this and i just don't have any ideas. I'm still running on a 2 or 2.5 amp fuse, it has never blown.

craig is alive and well. Inu found a slight tweek thats a good idea... 5pf across the 100k feeedback resistors to kill off slight 650 khz oscillations...

leakage current due to capacitance in the transformer... hook power supply ground to AC neutral thru say a 1K resistor and measure again. leakage current should be no more than about 1 ma.

If this is anything like when Inu got his finished, and decided to play hookey from work at lunchtime... We may not hear from craig for a few hours. And he will have a smile on his face that won't wash off.

Good luck with that problem. But remember... Its portable... It has a handle on the top. (actually 2 on that one)

Neither of those are going to work. You need a 1000 volt or more depletion mode mosfet that likes to work at a couple of milliamps. Use the 2sa1968 with +/-450 volt supplies, or use the ixys parts. Same thing with the required ixys parts in the power supply.

At least around here, you have a very good idea that you are going to get tenure or not way before you generate the application packet. As long as you have published enough and have enough references, it should be a snap. Too many WW2 professors finally dying off, and competent new blood is needed. Good luck Jim...

i spec'd 100 ma per high voltage winding, just in case you want to turn the bias up a bit.

Whether you run the output at 450v or 500v, you still need about 625 vdc unregulated for the bias regulator. So 485 vac (center tap is better but not required) is the target input voltage.

No ferrite beads on the original. No evidence of oscillation in my unit, now about a year old. andy has a problem in one channel of static that comes and goes, he has a scope, so will see if there is any oscillation... A ferrite bead might not be a bad idea.

So here is my comment on the "fake" parts. I've been stocking up on lifetime supplies of the semiconductors i may need in the future. When you get them in large bags, the bags have a label on them that says where they were diffused, and where they were packaged. The diffused is always japan, and the packaging is taiwan,korea,china... So the parts could be the real silicon, but just packaged inside of less than adequate lead frames.

there seems to be a growing interest in the phono section... http://gilmore.chem.northwestern.edu/kgphonoservo.pdf not counting the power supply, this is no more than $50 in parts if you use the lsk389, a lot less if you use 2sk170's... With the servo, matching is virtually unnecessary. I'm trying to find the moving coil schematic i did way back when...

Erno was one of the masters for sure. here is that article http://www.tkhifi.com/div/Erno_Borbely_fet_articel_2.pdf and part 1 http://www.tkhifi.com/div/Erno_Borbely_fet_articel_1.pdf

I think that andy's remaining problem is that the entire chassis is not fully grounded together in one piece, and a couple of star washers should fix that problem. But it does make music.

So here is a little historical fun. Back in 1975 and 1976 while in college i was building and selling world class phono sections and preamps. (sound familiar...) Virtually all of which are still in use today. So while some things like good circuit design seem to be timeless, other things like double sided circuit boards with heavy ground coverage are new. These days i would add a servo to the thing to make sure there was no DC on the output, something that really did not matter back then, as there were no fully DC coupled power amplifiers. I don't actually remember which of the riaa sections i ended up with, there were at least 3, so i showed the one from Robert Linsey Hood The original fets were ct134, which i replaced with 2sk170 in this schematic. http://gilmore.chem.northwestern.edu/kgphono.pdf this was one of the first boards without a solder mask. http://gilmore.chem.northwestern.edu/opampfront.jpg http://gilmore.chem.northwestern.edu/opampback.jpg

Well yes, but show me another audio product that uses this scheme. Then again, there would be virtually no reason most audio products would need to do something like this. Old tube Tek scopes did this in a few places mixing solid state and tubes.

Added an extra mounting hole for the power supply board. May add one or two more if i move a few parts around. The turn on thump is mostly due to the size of the transformer. The T2 actually pulls a bunch more power, but since there are 2 transformers, the thump only lasts about .5 second.

i've tried to get information on the tubes before. did not get anything useful. On my unit which by now has at least 800 hours on it, i have 2 6dj8's that went massively noisy. One happened at cj. But i am using old stock tubes pulled from tek scopes. The two tubes that went bad, i put on the side and recently put one of them back in, and sure enough it was definitely toast. But it still tests good on the tube tester. I'm still on the same set of output tubes, the chinese junk that i put in at CJ. On some of the original production T2's, stax put shields connected to ground around the tubes. Birgir's had the shields. I have a picture of another unit without the shields. The center pin of the tube socket is connected to ground, and the chassis is ground, so it should be easy to make tube shields. The T2 uses the input tubes in a way that i have never seen before, and i'll never likely see it again.

i'm sure c11 and c14 are correct. Q16 and Q14 may be in backwards, will look at that soon. D3 and D4 are 1n4746 which are 18v zeners D1 and D2 are 1n4737 which are 7.5v zeners This version has to run as a moving coil unit. Reason, the .1uf 1% cap and 750 ohm resistor at the output of the first part are one of the 3 riaa filters. Another version has the input resistor and pot replaced with a 47k resistor, and then the gain of the input stage reduced by 20db or so by changing around a bunch of resistors. a couple of other things fixed too.

try again 6 Band Resistor Color Codes or 5 Band Resistor Color Code Calculator

Brown Black Black Yellow Brown Red ==== 1 Meg 1% 50ppm ??

I love it when a plan comes together.