Craig Sawyers

IIRC my original T2 clone build gets to about that.

In fairness to the 2 transistor circuit, the original 1965 circuit used germanium transistors, Mullard OC44. Price in 1965? 8s3d from the Mullard price list, or in today's money 41p. Correct that for price inflation and you get £7.61 or $11, times 2 or $22, times 2 for stereo - $44. - for which you can now buy 4 AD797 or 16 LM4562 or 68 NE5532. The 1967 Quad 33 used the same circuit, but moved across to silicon BC109 - which were equally expensive back then. The 12 transistors in the 33 would have been the determining factor in the unit's cost. You can make that 1965/7 performance much better by adding a transistor (to up the open loop gain, and give enough drive current for the RIAA), something they probably knew - but that would have added a lot to the semiconductor cost. Which is all horribly irrelevant, since it is not going to be used!

The mag PU design was in a Mullard apps note from the mid 1960's, published by Dinsdale in Wireless world Jan 1965. You're right to leave it alone - the performance was marginal at best. In fairness to Stax they are running it from 30V, which improves linearity as compared with the usual 12V, and the emitter bypass on the second transistor of 100uF kills of capacitor nonlinearity - so they thought about squeezing every ounce of performance out of mediocrity. It's noise performance is either dominated by the 2.2k resistor in series with the input, or the poor noise performance of the first 2SC458 transistor (16dB noise figure at 30Hz). The red line is the correct treatment!

I take my hat off - that is a thing of beauty.

^This

From a purely thermal management point of view - absolutely, 100%. But from the product safety perspective to CE or UL, the general rule is 25C above ambient (to max ambient of 40C and external part temperature of 65C) for touchable anodised casework - and an external heatsink counts as casework. So most manufacturers of power hungry audio gear now put the heatsinks inboard. Like Krell and Emotiva - but not interestingly Mark Levinson who still put their heatsinks on the outside and don't bother to certify for external temperatures.

I'd do it somewhat differently - release final Gerbers, BOM etc but only to those on the list who are (a) trustworthy (by some criterion like long term, regular contributors, no newbies etc (b) agree formally not to release to a third party. Something like that might be workable and prevent blatant commercial design duplication. Probably achieve nothing other than satisfaction, but why not send a letter to the Russians who are selling the BHSE. Also I know Brian Sowter - I am sure he would be devastated to know that he is supplying his attenuator transformers to someone ripping off the hard work of someone else.

If it isn't the Chinese plagiarizing products it is the Russians. In a business meeting a year ago or so, the visiting guy had been shown the inside of a unit in China where they had a team of 200 whose job was to decompile embedded code, FPGA code, ROM contents etc of Western products. We don't stand a chance in hell against that level of industrial scale ripping off.

I sure hope they are paying Kevin a royalty on sales. The Sowter (UK, Ipswich) attenuation transformers used are really good though, and very well thought of.

I've got a forward looking one that is not in the car at the moment - the micro-SD card died. New one on the way. But if I was doing this again, I would have the variety that looks both forward and backward so you can record rear end collisions, or car park damage.

Easy thing to check with a thermocouple for anyone with a carbon or kgsshv. The caps in the KG-T2 probably get pretty toasty, but that animal drags ~200W out of the mains, the transformers run hot, and there are two massive heatsinks along each side of the case that also get hot. So although I have not measured the temp of the reservoir caps I suspect that they get pretty hot through association with their surroundings. But noone is gong to leave the T2 on for much longer than you are listening; I let mine warm up for an hour (two max).

OK - I'll bite - what is KR, ( M ?

This was too good to be true. So famous that Wikipedia has an entry, with first sentence (wait for it) "Vera Coking was a retired homeowner in Atlantic City, New Jersey whose home was the focus of a prominent eminent domain case involving Donald Trump." https://en.wikipedia.org/wiki/Vera_Coking

All down to Arrhenius for semiconductors. And electrolytic capacitor life about halving for every 10C temperature increase. Not counting infant mortality. And thermal shock every time it is turned on. So in this context, what do you mean by MTBF?

I was wondering that too - I don't immediately recognize the glass envelope.

Well bugger me - I'm British through and through back as far as I've looked (late 1600's) and I knew absolutely none of that. Other than that there is a City of London, I had no idea of the inner machinery.

Happy birthday!

The other thing to work out is which end of the primary winding is next to the secondaries. You really want the hot or live input to be next to the core, and the neutral or low input next to the secondary. It will of course be perfectly OK the other way round, but makes-borne noise coupling via the interwinding capacitance much easier. As far as I know there is no straightforward way of figuring that out.

Somewhere I have a photo of some poor sod's old man after he peed against an electric fence. Imagine you took a blow torch to a sausage, for several minutes.

Yes - Dalbani were the outfit that supplied me with junk 2sc3675's. When I put one or two spares on the curvetracer they broke down at 400V or thereabouts instead of 900V minimum. Avoid Dalbani like the plague.

$6+ seems to be what 2sa1968 are going for now. And there is no guarantee that even they are genuine. A 20c part is almost certainly fake IMHO. I'd say you have some major problems.

^Every time - every damned time - you reduce me to gales of laughter

That indeed is a good point given that the main semiconductors are long obsolete. My T2 went together during the first builds with fake 3675's and actually produced sparks. Killed just about every bit of silicon as collateral damage.

Current world pi memory record 70,300 digits http://www.pi-world-ranking-list.com/index.php?page=lists&category=pi took more than 17 hours to recite it. I actually saw a guy back in 1976 who only had only 10,000 digits, but had it in random access - given any three or four digits at random from the number he could continue from that point immediately. Same event (at CERN) that Wim Klein extracted the 73rd root of a 500 digit number in a little under 3 minutes. Klein's party trick was going out for a beer, and walking though the car park would memorize all the number plates and make/colour of each car. People in the bar would test him - he never got it wrong. He was employed by CERN to debug computer code - he was capable of doing a mental dry run to find tricky errors. Good heaven - I found a photo of that event on the web. I'm five rows from the front, 3rd from the right, checked shirt. Klein is standing, and the guy sat next to the projector is the pi man - totally forget his name. http://www.symmetrymagazine.org/article/december-2012/%E2%80%98human-calculator%E2%80%99-wim-klein-advanced-physics-inspired-others

Are both channels the same in this regard? If so, have you checked that the LED's are the right way round, and the 100V zener is the correct way round?