kevin gilmore

yeah... please don't do it that way. The alumina insulators really are required. The plastic #6-32's definitely work plenty fine.

I want to make the kgsshv absolutely trivial to build, and want to make sure that people know how to mount the semiconductors. For all the TO220F transistors, a hex head #4-40, a #4 plastic washer, the transistor, a thermal pad, the heatsink, then preferably a belleville washer (which i can't find stock on) and a nut. So for the 2sa1968 version, that leaves only the ixys parts and the low voltage regulators. The small heatsinks are #6-32 tapped. So you have to go with a plastic screw. For the ixys parts, thats the plastic screw, the transistor, the aluminum oxide insulator, and the heatsink For the low voltage regulators, all you need is a screw and a regular thermal pad. The #6-32 lexan screws are pretty strong it seems. unless someone knows where to get the screw tabs that are #6-32 on one end and #4-40 on the other end.

i asked this to marc and craig in PM's, but i might as well ask here. Anyone know the voltage ratings of a TO220F package? Specifically if i put a metal screw in the hole, how many volts does it take for the package to break down between the screw and the collector tab inside. Has to be well into the 1.5 to 2kv range right? I've found some new polycarbonate (lexan actually) screws that seem to be extremely strong, but still metal screws are better.

I think the designs of the servo's are such that the amp reaches and maintains the correct dc voltage very fast, certainly less than 5 minutes. On original BH's, it usually takes about 20 minutes for stability. BHSE is probably a bit quicker at 10 minutes. The tightly regulated power supplies also make a significant difference.

Rule #1 Never mess with high voltage at the end of a day when you are tired. Rule #2 Always remove the lead from the AMP terminal on the DVM as soon as you are done measuring current. Yep, i fried a meter once. It was more than 20 years ago. Half a dozen DVM's around the house, including a couple of $19.95 cheapies makes things a lot easier.

After doing 20 chassis and board sets... cheap really is not in my vocabulary. I very much doubt that even ti khan put $30k pretty much all at once into a multi year project that ended up loosing money For what nelson is doing, these are clearly great devices, regardless of cost. I like the new devices that Dan is using better, they are bipolar obviously, but can't handle the voltages. I definitely want to test at the voltages and currents we need. One of the depletion mode fets as the current source, one of the enhancement mode fets as the grounded grid output amplifier, and then probably a 2sj79 or something similar as the cathode drive should make a great output stage, if it does not oscillate or do stupid things at low currents. The active battery is good as is, and the toshiba part will replace the 2sc3675 with a bit of tweeking, and the ultra stable voltage reference now used in the kgsshv power supply is also a great idea. So it seems that the 2sj79 and 2sk216 will have to stay, as far as i know they are still in production.

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.