kevin gilmore

anyone know where to get the rubber versions of these things https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=1938&GroupID=545

Frank's son is evidently practiced in the ways of pabbi1. Not a good thing. Not even for a few minutes.

So i'm definitely done sans knob and inductor. I measured my chassis length as 13.035 with this http://gilmore.chem.northwestern.edu/bigger2.jpg (yep its an old picture) Which kind of makes sense when you add .125 in addition with the plastic bezels and things don't fit right. If you wanted to make it perfect with the current circuit board, then a chassis length of 12.875 makes more sense, then you notch the plastics for the board. Then everything fits flush. http://gilmore.chem.northwestern.edu/dsavitsk5.jpg you can see the grounding lug on the inside of the right screw. I kind of like it better without the cheap plastics anyway. I put in 2 x 30mm holes for the tubes. http://gilmore.chem.northwestern.edu/dsavitsk6.jpg Which gives enough room to get a tube puller in there on the base of the tubes.

I love it when a plan comes together... The whole design of the amp is to minimize the lengths of the audio traces. So the pot is in the back, the input tubes are in the back, signals go from the back to the front and then out the front hole. There are lots of amps that do it backwards, which makes no sense. The BL vs GR version thing completely makes sense. Even at 8k, there is still plenty of adjustment room, because once you get it to turn on, on that pot, .25 turn is all that should be needed.

I'm going to make another comment, and this is one of those philosophical things, some people do it one way and others do it completely differently. If you pay attention to underwriters laboratories, and the international electrical code, then for SAFETY reasons, the 3rd wire of the iec connector goes to chassis ground. Pretty much everyone agrees with this. Two wire power plugs are another thing entirely, and are real bad for audio as there is always a resistor between neutral and chassis ground (or the whole thing is double insulated) Remember this is all about safety, not good sounding audio. But for minimum noise and ground loops, it is usually (but not always) better to completely float the circuitry inside from chassis ground. The rca jacks certainly allow for this, and so does the neutrik jack. That is not possible given the current layout of the board. For smaller systems with just a source and this amplifier, it is not going to make any difference. Mix it up with a pile of other electronics, and it might cause trouble. For example on my T2 there is a toggle switch inside the amp chassis that can disconnect circuit ground from chassis ground.

And that is in fact what i ended up doing. I tried it against the smaller boss on the pot, and that did not fit right either. I'll try again tomorrow and add a very thin spacer to the pot to get the panel off the outside boss. If there is a part number for extra aluminum front and back panels, i can certainly try again. My chassis is definitely longer than the circuit board. Probably by at least .075 Its clear (at least i think) that the back panel has to be snug with the iec socket and the rca jacks. The main part of the rca jacks. This is where at least .035 of the difference comes from. If you do it the other way then the amount of ground available for the rca connectors shrinks, and a number of the rca male connectors i tested don't fit in all the way and are loose. The mounting hole for the rca jack was designed to be a self tapping screw for plastic.

the parts stuffing is on page 3 http://gilmore.chem.northwestern.edu/staxt2nc3fdh3.pdf if the active batteries are not conducting then many of the led's will not be turned on. Adjust RV2 to decrease the resistance, (i think) When things start to conduct, small changes will cause the amp to flip flop back and forth. Until both sides of the amp are balanced. Its a bit tricky, but once you figure it out, its not too bad. Yes the led's run at low currents. But from the picture i posted, they do in fact light up pretty well. Definitely not dim. Also measure the voltage across R42. If its zero, then there is a problem with the 2sk246

My unit is complete and works fine. Very quiet for a tube amp. Will swap to the inductor when it shows up. Going to add 2 more holes in the back panel and add a grounding safety wire there, and put tube holes in the top panel tomorrow.

The other trick is what to do about the top panel. Some of the tube sticks up, but not much. So there would have to be a fairly large diameter hole, otherwise there is no way to pull the tubes out. Or make reasonable holes, and slit the cover in two, so you slide the cover out to change the tubes. I'm kinda leaning towards that approach. The final parts just showed up. Gotta go... There are plastic ends available, which are one piece, and would fit perfect. And be much easier to machine. Overall, pretty good for a first round.

Yeah... About that... The board is not long enough, and the parts don't fit thru the panel right if you put the plastic piece on first. !!!! So if you assemble it correctly and push the board to the back end, then the front end parts are .126 inches off. Now for me its easy, just take .2 inches off the chassis. But i would have to do it at work because i would take 1 swipe with the top on, and i need a 4 inch long end mill for that. And a much bigger mill. height of the case measures 2.0935 (back/front panel not including the plastic surround) height of the center of the iec hole is 1.0595 from the bottom (center of ground pin) all 3 screw holes should be #4-40 body drill size. diameter of the hole for the rca jack to fit the plastic thru is .4055 inch I will add 2 more holes to mount the iec jack to the back of the back panel

If you insulate the lm338 with a thermal washer and plastic mounting washer, it should be easy to secure the heatsink to the chassis. the rest of the parts should be in today. And i got a bit sloppy with the machining as its very hard to hold stuff this thin down... http://gilmore.chem.northwestern.edu/dsavitsk1.jpg http://gilmore.chem.northwestern.edu/dsavitsk2.jpg http://gilmore.chem.northwestern.edu/dsavitsk3.jpg http://gilmore.chem.northwestern.edu/dsavitsk4.jpg Now that i know the exact dimensions it should be easy to make new panels perfectly NC'd out of .125 material that is thick enough for me to hold it in place.

these are actually great caps, available from mouser, and reasonable. And they fit too. 598-936C4W4P7K-F

No guts, no glory. Check things over 9 times and then have at it. As long as there are no shorts on any of the current sources, no parts should fly. Make sure all the pots are set in the middle, makes things much easier.

While you are at it, you have to jumper the wires on the side to the pot too...

You forgot to jumper the primaries on the transformer A to B and C to D

dact mounting brackets and a custom piece for Inu http://gilmore.chem.northwestern.edu/t2bits.jpg definitely on schedule for stax jacks next week and more angle brackets the week after.

Yep, titanium. Very hard to machine correctly. Need special carbide tools, and if you don't get the feed rates right, the tools shatter. Or the surface ends up with golf ball dimples.

Yep, bizarre, but that is the way it works.

What better way to show the surface finish. Macro lens Paging Dr. Wood... Paging Dr. Wood...

birgir's knob http://gilmore.chem.northwestern.edu/birgirknob.jpg It is not polished at all, strictly micromachined. Even the fingerprints show up... Amazing stuff. 4.5 hours of actual machining time. 100 turns per .0001 inch. 2 passes front and side.

Well it is soldered in, so if there was an offset i got it right, but i did try it first, and it fit both ways. The output transformers are definitely offset and can't be put in backwards.

birgir's knob is done pictures later today when i get home.

lets try that again mje350 ECB across the plastic front.

The mains transformer can be put in backwards. So pay attention to the wiring of the transformer and compare to the board. Also the shield is soldered to a pin which really should go to circuit ground. too bad there aren't any connex 7 pin teflon sockets. very hard to tell the direction of the led's, so first test the led to make sure of direction, then look at the schematic to make sure you insert it right. I'm as far as i can go until the rest of the parts show up. Should take no more than 2 hours to fully stuff it. Cutting the holes in the back and front are going to take more time. as far as i can tell all of the mje350's are BCE across the plastic front...

I tested at 10% over maximum rated load (which is dc because its pure class A) out of the power supply with a stack of resistors. The leads out of the high voltage transformers are 14 inches long. And yes you have to tell them to do 600 vac wire for all of the transformer windings. Which SumR does anyway i think.