Craig Sawyers

Thanks for the heads up - I'll watch that one when I build mine up. Great to hear that the beast lives, and sounds great! Can hardly wait. Mrs S picked up the credit card bill today, which had lots of money to Mouser, Farnell, Dalbani etc on it. It sure was an interesting conversation (not)

Inu - tell us more, more more!

Good it got to you in good shape, Kevin - massively looking forward to what comes out

Lifetime (MTTF) data on specific transistors is very difficult to pin down. Generically for silicon at a junction temperature of 150C it seems to be around 10^6 hours, or 100 *years*, assuming it is a chemical activation process - defects, contamination etc. People do elevated temperature testing to reduce MTTF to a few thousand hours and then extrapolate. There is an arcane paper here http://rel.intersil.com/docs/rel/calculation_of_semiconductor_failure_rates.pdf that sets out some detail.

I was lucky enough to see the 1982 Footlights Review while at Southampton University. Imagine Steven Fry, Hugh Laurie, Emma Thompson and Tony Slattery together on stage.......

Really glad they sound great! Fine speakers. Regarding bases, Quad restorers tend to collect a rouges gallery of bits from speakers that were not economically repairable and are scrapped for spares. I would imagine that Wayne would be able to dig out a couple of suitable bases. If not let me know - I'm sure One Thing in the UK will have precisely what you want - and they ship internationally regularly.

I kind of reckoned that I'd defaulted to lecture mode quite enough for one day . I do have a habit of banging one once I get going. But you're right - with the plastic package you get one layer of grease, and with the alumina you get two. So add another tenth or so per layer.

It doesn't go anywhere as such. The only thing that matters is the temperature of the silicon. That is usually taken to be 150C or thereabout. So if you are bolted onto an infinite heatsink, the thing that determines the temperature of the silicon is the package thermal resistance. So, if the TO220 metal package dissipates 178W on an infinite heatsink with 0.7C/W, the silicon temperature rise is 178 x 0.7 = 125C, plus the heatsink ambient of 25C = 150C. Similarly for the plastic package, the silicon temperature rise is 59 x 2.1 = 124C - the same number (within the accuracy of the numbers). If the heatsink is hotter - because in the T2 there are lots of devices attached to the same sink - you have to derate things further. The total calculation involves adding together the thermal resistances, in this case package + heatsink-air, so 2.1 + 0.3 (guesstimated) = 2.4C/W. Assume heatsink temperature is 35C. So maximum device dissipation is (150 - 35)/2.4 = 48W. For the metal device, we have to use a heatsink insulator - which is say 2C/W. So we need to add up package + insulator + heatsink-air, or 0.7 + 2 + 0.3 = 3C/W, giving a maximum dissipation of (150 - 35)/3 = 38W. Of course, you would not operate a transistor die at 150C - you'd derate it to <100C for long term reliability. Which would mean max device dissipations of ~27W and ~22W respectively. But anyway, the upshot is that the plastic packaged device gives better thermal performance. The only way to equalise them is to reduce the thermal resistance of the heatsink insulator for the metal package to ~1.4C/W - but we're stuck with alumina which is 2C/W for a TO220. Running some quick numbers the T2 devices run around 5W quiescent and perhaps 10W maximum - so safely inside the dissipation limit with an alumina insulator.

The trick with getting good TO220 thermal contact is to apply the right fastening torque, particularly with the elastomer insulators (but also with hard insulators like mica - or alumina). The spec depends on manufacturer, 0.8 - 1.1Nm (7 - 10in/lb) in one case and 0.49 - 0.686Nm for Sanken. Beyond that the tab starts to deform enough to lift the pressure off the body - the package sort of pivots upwards. I though that the plastic TO220 could take more torque - but the specs do not indicate that - the same as for the metal tabbed version. I bought a torque screwdriver a few years ago for precisely this purpose - and the correct torque is surprisingly slight. When hand tightening, I've found that the tendency is to massively overtighten. As you increase torque, the thermal resistance falls to a minimum, and then increases again as you tighten more. The way around that is to use a hole-less insulator, and one of those spring clips that bear in the middle of the transistor body. Keeps voltage isolation high, and applies much more pressure since there is no risk of pivoting. The problem is that you need a heatsink extrusion with a feature into which the clips engage.

But that is down to the total thermal resistance. Junction to case is 0.7C/W for TO220 and 2.1C/W for the plastic case - a ratio of 1:3, which is the same ratio as the maximum power dissipation (ie 178/59). But for the TO220 you need the ceramic insulator - which is 2C/W. So the total thermal resistance for the TO220 plus alumina insulator is 2.7C/W as compared with 2.1C/W for the plastic. So the plastic should actually dissipate more power than the TO220 in the T2. It is also stiffer than the metal tabbed TO220 (which is a nightmare package to bolt down and keep it in contact with the heatsink), so should stay in contact over its whole area with the heastsink.

For anyone who hasn't been watching Glastonbuy, do a You Tube search for Matt Smith Glastonbury. To cap one evening off, he did a 5 minute set with Orbital of the Dr Who theme tune. Enough whizz bang special effects to blow your mind - and I speak as someone who has seen Jarre twice. Treat yourself and watch.

Well, apart from the 2SC3381 both boards are now completely stuffed. I'm getting a little wary of pushing those into the holes though. Although KG opened them out a tad, just enough to leave some plating on the inside of the holes they are still reportedly a very tight fit. The holes seem to be a tad under 0.6mm - a #74 perhaps (0.57mm). I need to stock up on carbide circuit board drill bits anyway, so I have put a couple of 0.65mm on the list. Across the corners of the square pins is 0.63mm (2SK389's actually measure 0.59mm) - so an 0.65mm should work nicely. The downside is that 0.65mm will definitely take out the hole plating - so I'll have to carefully solder both bottom and top side pads. I'll report back once I have the drill bits and the 2SC3381.

Wow - well spotted! It is indeed a TDL transmission line speaker. They are one of the few companies to tame the somewhat wooly bottom end of a TL speaker. Still around History

You have no idea what relief that comment means! The number of things I have that have made it to circuit layout, board manufacture, stuffing then stall when it comes to the boxwork. Apart from finishing stuffing the KGT2 (and thank heavens the Kevin has done the casework design and is supplying to us builders), I too have be de-shelving a dynahi this weekend with the determination to finish the darned thing off. And that is just the start.

Or www.rswww.com at 99p each, their part number 671-5199 - where I got them from. Their website is down at the moment - they often do site maintenance at the weekend.

ELECTRONIC COMPONENTS, SEMICONDUCTORS, PARTS, TRANSISTORS, INVERTERS, TRANSFORMERS | DALBANI

Just took the car for an MOT test (in the UK every car over 3 years old gets a roadworthiness test; takes an hour). Horrendous traffic so I arrived 10 minutes late. Guy refused to do it. I was not a happy bunny. Been going there 18 years - so much for loyalty. Last time too - time to go somewhere else I think.

Semis just arrived, with the only waited for item being the 2SC3381GR. Luckily judging by Inu's post I've got 2SK246GR and not BL. At least I can stuff every semi not heasink mounted (apart from the '3381s) now.

That got me thinking. Doing some calculations, the LED's are all operating at reasonably low currents - either 1mA or around 0.5mA. So they will only light dimly, and from the datasheet develop 1.8V. I'd start looking around D24, Q30 and Q31. These are current sources for Q4, Q5 and provide the current through the batteries. This current should be 1.8 - Vbe = 1.2V across a 240 ohm emitter resistor - or 5mA. In addition if something is screwy with the circuit around D1, the biassing of Q4 and Q5 will be up the chute. One or both of those could well put the battery into an inappropriate regime - if it is expecting 5mA and is getting significantly less for example (I haven't figured the circuit for the battery yet). Er good luck - I'll be in the same place as you in around a month's time.

Looks awesome! Turning on power for the first time is a really sweaty palm moment. Always. The only insurance is to check, check - have a cup of coffee and go for a walk then check again.

Stick with it - it grows on you as you get to know the characters. The musical numbers are not quite up to Family Guy standard (who can forget the FCC number), but pretty good nontheless.

Mongrels. Late night BBC adult puppet show about a group of animals (fox, pigeon, dog, cat etc). Voiced by a selection of comedians - hilarious. Currently at episode 3.

Luther = superb. Shaky start while it found its feet - but excellent later in the series.

Finished the power umbilicals today (getting everything prepped for the arrival of casework in due course). Forgot how fiddly it was to wire up Amphenol mil spec connectors. I guess it took an hour or two to cut the wires precisely to length, twist the heater wires (to reduce hum radiation), pull though mesh sleeve and adhesive lined heatshrink the ends. Then cutting up neoprene sleeving to the correct length (around half an inch). All told maybe 4-6 hours for the pair. After soldering one end I did a pin to pin check to eliminate wiring errors (one found and corrected), and a leakage check to ensure that there were no faults in the ubmilical or the connector. Used an AVO mega-ohm meter, which has a switchable voltage up to 1kV and measures up to 10Tera-ohms (10^13 ohms). Well the leakage of my test setup was 10^11 ohms, so all tests were relative to that (to get much further the whole set up has to be on a teflon sheet). Every pin was checked to every pin, and it was all well over 10^11 ohms at 1kV for every wire to every wire - which is an excellent result. Very happy with that. I made them up at 4 feet at KG's suggestion - that allows the units *not* to be stacked, so helping heat build up.

I didn't watch Life on Mars, but entirely intend to. I only watched the last season of Ashes to Ashes and it was unremittingly excellent, with a really stunning final episode. So let me see - I need to watch two seasons of Mars and two of Ashes - but it is going to be so worth it judging by season 3 of Ashes.