Craig Sawyers

<grin>. The Tek 575 transistor curve tracer has precisely two (germanium) power transistors in the step amplifier. Every other active device is a tube. Not totally suitable for the transistors we're concerned with - maximum base step is 0.2V (so not high enough for the FETs) and the basic instrument will only do 200V sweep. The mod-122C version goes to 400V sweep, which is still not enough for the high voltage bipolars in the T2. The only two golden oldie Tek tracers that will do the job on T2 semis this are the 577 and (if you have deep pockets - which you need for tackling the T2 in the first place) the 576. I'm using a 577 for my measurements.

Jeez - is there no end to the junk semiconductor hell we seem to be going through on this build? Even the brand name seems to be counterfeited judging by Justin's Sanyo-stamped C3675's that have a beta of 4 (spec = 30 minimum). I've just decided to pull the four J79's too and verify them on the curve tracer. Tomorrow. In 35+ years of electronics design and build I've only ever had one out of spec device until now - and that was a 74S-something in which the transition times were out of spec and was generating a few nanoseconds duration glitch. In 1982.

With a bit of luck my batches of C3675's will arrive tomorrow. To prepare for that, I've pulled all the suspect 3675's and checked them on the curve tracer. Two from the batteries were shorted. All the others on the heatsink survived, but had beta between 6 and 15 and had premature breakdown at 550V to 650V. All but one of the eight K216's were also dead. So the heatsinks now only have four high quality C3675's, the A1486's and the J79's. Still need to pull the dead 100V zeners and dead LED's. I hope that has extricated all the demons. All the board mounted 3675's are high quality ones.

Yeah - that is really excellent service! The key about the expansion issue is that wood is not isotropic. Along the grain there is hardly any change. But perpendicular to the grain you can expect a movement of 3% or more depending on changes in humidity. Think of wood as a bundle of drinking straws - there can be very little movement along the bundle, but rather a lot across the bundle as you squeeze. The legs of this stand are along the grain direction, so doesn't change much. But the bit of the shelf that fits in the notches is across the grain, and will swell and contract as humidity changes. Not instantly, you understand - but it will certainly follow seasonal changes. The only way to equalise out the anisotropy is to make plywood, where alternating thin layers of wood are arranged with alternate layer's grain directions perpendicular. That is the basic approach needed when veneering (at least in modern times) - a core material has cross-banding layers glued to it. The veneer goes on top of the cross-banding.

Glad you're getting a good resolution in the end, but I suspect that it is a design problem at the root. The verticals are long grain, which hardly moves at all with changes in humidity. The shelves are short grain (vertically), which changes dimesion quite a lot with change in humidity. Having a quick look, assuming a generic hard wood and that the shelves are 2" thick, and that the moisture content goes from 8% to 5% (typical between summer and winter, air conditioned or not etc) gives a dimension change of 16 thou (0.4mm). So a snug fit as manufactured at 5% can lead to an impossible interference fit at 8%. These effects are real. Large woodworking benches have to constructed to try to prevent the wood from splitting between winter and summer (for example the end caps are on sliding splines and fixed by a single bolt - ie not glued. End grain/long grain problem). I finished building mine in the winter, and by high summer some of the joints had moved by way more than a millimeter. Now that it is winter, they have all closed up again. And this timber is 4" thick, quarter sawn beech. Same thing with fitting drawers - you leave around 1.5mm clearance at the top if you build them in the summer, so that when the wood expands in the winter it does't jam. If you build in the winter you can cut the clearance down. If the drawer really jams as humidity comes up, there is absolutely nothing you can do until humidity drops again, it will be stuck fast. So if Arnold builds yours up at high humidity, the shelves will be slightly loose in the summer. If he builds at low humidity, there will be no way on god's green earth that you will be able to dissassemble them when the humidity comes up - they'll be jammed hard

Top Gear (second part of the Christmas pair). Fairly average I thought. Then the Dr Who Christmas episode. Fairly average I thought, although Michael Gambon is always a pleasure to watch. Earlier, Inception on pay-per-view. Excellent.

I know it is FET's rather than tubes, but Erno Borbely used this scheme in many of his products, detailed in "JFETS: THE NEW FRONTIERS,PART 2", Audio Electronics 6/99, 16-20. He did not use cc loads on the top drains, but has a cc load on the long tailed sources. I downloaded it originally from Erno's site, but he has now shut down the business and taken his site down.

Sounds like a great day (apart from your sister-in-law's troubles!). Sure beats the hell out of frozen up burst heating pipes, which happened just before Christmas. Bonehead house builder had run unlagged and uninsulated pipes above our entrance porch - so thermally essentially outside. We've been way sub-zero for the last two weeks. When they thawed a little one day when the temperature crept above freezing, water came out of the split pipes under full heating pump pressure - it was a truly impressive sight. Got everything isolated and turned off while phoning the plumber, who got there half an hour later. By then I had pulled the closing panel off, saw the exposed pipes, and was having fantasies about finding the builder and laying about him with a length of two-by-four. The good news is that the burst was *outside* the house, so there was no damage to the house at all. Now properly pipe lagged and joists insulated above and below with high grade lagging. It ain't gonna freeze again.

The alternative, used on old Krell power amps (and many high power pro amps) is to have a power resistor in series with the transformer which is shorted out by a relay after a second or two. Various delay circuits are used, either discrete component or 555 based. It has the advantage, as compared with a thermistor, that the impedance in series with the transformer winding is kept to a minimum.

Interesting - I was planning on doing precisely the same, having got a ton of Mullard 6DJ8's from an old and sad 535A. They all measure right on the money, so it will be interesting to see if I get a similar noise problem. Perhaps I'm missing something, but it seems a differential pair cascode with constant current loads

Kevin - any insight from Stax on this? Is there any indication that they selected 6DJ8's, or that the screening can on the original T2 played a critical role? Now 22:40 in the UK, got a belly full of excellent food and booze - so I'm retiring to a place of horizontal repose.

Fantastic news! Is that number 3? KG, Inu and now Blubliss? I'd definitely be #4 if the XXXXing C3675's had arrived before a 4-day holiday. But they didn't, so I'll have to slum it with a BH for a while longer

I just love the endless variety on these lists. There is whole musical subset that operate at a level I could only aspire to. I did look at that exercise linked above, and it brought back the grind of learning the clarinet. Mind you, having mastered a bunch of exercises, it never failed to amaze me that a horrible sequence of notes in a real piece would magically just fall under the fingers, with one part of the brain thinking "I wonder where that came from?". Of course it was buried somewhere in an exercise and had got hard wired into the wetware.

I'll bet it tastes great though. Here's what I do with regular cheddar - toast some bread. Slice on cheese. Sprinkle with chilli powder (critical step) and put under grill. Cheesy heaven.

Sounds like a great company do. Wisconsin Cheddar? I buy my cheddar here [ATTACH=CONFIG]4136[/ATTACH] An outstandingly fine non-pasteurised, 18 month matured cheddar called Montgomery. From Yeovil, Somerset Montgomery's Cheddar, world-class unpasteurised, natural cheese made by hand : West Country Farmhouse Cheesemakers : Handmade Westcountry Farmhouse Cheeses .

I thought the drive by shooting of effigies of The Stig was pretty good. Interesting that under Tiff Needell's tender care Danny Boyle did a really great lap time in the Reasonably Priced Car. The concept of The Stig had kind of run its course anyway.

Yeek! For some reason it made me think of that Soprano's episode when Tony used an industrial staple gun on a guy who'd crossed him...

Always look on the bright side of life - it could have happened over Christmas.... Seriously, hope you get over it soon. Food poisoning can be very very nasty. Must have been something badly off (fish? eggs? - or fish eggs?).

I will say this only once.... The main actor (played Rene), Gorden Kaye (yes - Gorden, because Equity misspelled his name) was darned near killed is a massive storm in 1990 that cut a swathe through the UK and mainland Europe, with over 100 deaths including Germany and France. Kaye ended up with emergency brain surgery (completely successful) after a chunk of wood was propelled through the windscreen of his car and hit his head. He's still got massive scars on his forehead to prove it. The BBC account of the mayhem of that day his here BBC ON THIS DAY | 25 | 1990: Children killed in devastating storm

Ah - the logical opposite of Sgt Pepper, I see....

Struts - I know you've answered your own questions, but I thought this might be worth elaborating. The chassis components are all anodized, which is a very good electrical insulator. With such high and lethal voltages I was concerned that isolated chassis components could be a significant hazard. The rear of the mains chassis plug is a case in point. I drew a pencil line around the ouline and then carefully used a dremel with grinding attachment to remove the anodizing behind where the plate mounts. I also dremelled the anodizing off areas when the chassis parts bolt together - the front and back plates where they mount to the heatsinks and top and bottom, the top and bottom where they mount to the heatsinks and front and back plates etc. So now all chassis components are decently electrically bonded. The ground wires in the PSU and amp were fixed with butch star washers to the spare holes in the heatsinks in accordance with safety standards. I might blow the bugger up electrically (and have done) but once it is working and cased up it will be safe

Well in my case the C3675's in the battery went short circuit. That massively overloaded the bottom K216 which went short. That massively forward biassed the 100V zeners, which glowed briefly before blowing. The chain of failure also took out D6/D7 by massive overcurrent. Which is why I recommend testing your C3675's for DC current gain (ie *not* small signal slope gain) at 5mA, should be 70-ish or more for good 'uns. 20V is quite enough to test at, and assume that the gain increases by around 10% by 740V (because of the slope in the collector characteristics).

I agree. Dead 100V zeners seems to mean dead K216's. Been there, got the badge (root cause for me, crap C3675's). Don't beat yourself up too much about the wiring error - the good news is that one channel survived the trauma. This circuit seems to be a fascinating mix as tough as old boots, and also kind of frail at the same time. Incidentally, got 115 C3675's coming from three different sources now. If all are good, that is a result - plenty for other projects. But three sources hedges my bets - all three lots are unlikely to be simultaneously flakey.

Ah. Maybe not. Test D10 and D11. If they are kaput, check the 100V zeners and the K216's on that side.

Gate-drain short in Q22? One or all of the 2SA1486's the wrong way round? Wrong values for R33 and R34?