Craig Sawyers

You also need to be careful on tightening torque. For correct assembly, the torque is surprisingly low. I bought a torque screwdriver for exactly this purpose. What insulating bushes and washers have you used? Have a look at https://www.onsemi.com/pub/Collateral/AN1040-D.PDF Basically overtightening can distort the semiconductor package and compromise thermal transfer, and that you have split the insulating bush suggests you are massively overtightening the fixing screw. Craig

Even Madrigal/Mark Levinson (like the No33 spec) have performance data generated by muppets. RMS Power - there is no such thing. Well you could in principle calculate RMS Power - but it is a meaningless number. The only meaningful audio power is Average Power. See for example https://www.analog.com/en/analog-dialogue/raqs/raq-issue-177.html

Any idea what the amps are?

"Linn’s innovative Bedrok™ sidewall technology. This technology uses special beech plies that are compressed under high pressure, creating a solid and dense material that reduces unwanted vibrations." AKA Panzerholz from Delginit "Beech-based Delignit® materials feature special technical and mechanical properties (e.g. friction wear and resistance, dimensional stability, breaking load). Beech is one of the toughest and hardest types of wood. It is just 1/10 the weight of constructional steel but has 1/3 of its rigidity. Wood products also represent long-term storage for environmentally damaging CO2 (one cubic metre of wood absorbs almost one tonne of carbon dioxide)." "Panzerholz® A DIN 7707-compliant hardened panel material made of a combination of phenolic resin and hardwood with a hardened structure." https://www.delignit.de/en/brands.html . These guys also do bulletproof versions. In Panzerholz they apply high pressure to the ply makeup before the epoxy goes off, so it ends up much thinner and higher density that just regular plywood. It machines beautifully, can be epoxy bonded (white wood glue does not work), and can be polished to a fine finish. You have to hide the ply edges, (by a 45 degree mitre) or use them as a design feature. It is astonishingly well damped as a material, and stiff, which is why it has been used in audio products, including loudspeakers. I has actually been machined to make entire plinths, by epoxy bonding thinner plies and NC machining, or for my slate plinth as a simple 25mm thick support plate. There is alas little mystery regarding the "innovative Bedrok™ sidewall technology"

I have a few that almost never get used. My go to methods are ratchet straps and a selection of gizmos to protect the work, or Bessey clamps, like this https://www.besseytools.co.uk/bessey-die-cast-zinc-screw-clamp-lm20-10-200-100 which are not cheap, but are exceedingly good. I have quite a number in different sizes.

Happy birthday Birgir!

alternatively

Happy Birthday!

Who noticed that the kid on the left has a poorly thumb? I reckon it was misusing his weapon and getting his thumb trapped by the recoil, or burnt on a hot bit. Not a good advert indeed.

Welcome to the over 60's club Kerry! Have a great day!

🤡

This could go here, or on a drinks thread. This is a picture of the ultimate in home entertainment in the 50's. On the right there is a radio, and above it a record player, and the white speaker grill below. Mono of course. On the left, there is a cocktail cabinet with record storage below. Nothing like getting quietly hammered while listening to music. It is not mine BTW.

Some British guys blowing up small electrolytic capacitors by putting too much voltage on them, in slow motion. Like they said "don't try this at home"

He cut down on the booze in his later years. His last stage play, Private Lives, he did stone cold sober. He says in his diaries that it was the scariest thing he has ever done - everything you have ever seen Burton in, movies, plays etc he was boozed up just enough to overcome stage fright, without losing the ability to act. Acting: pretending to be someone else, for money.

Burton died at the age of 58 from a cerebral haemorrhage, the cause been a life of chain smoking and a gargantuan amount of booze. I've read his diaries, and at one stage he congratulates himself for cutting down - from three bottles of vodka a day to just one. It is a wonder he lasted to 58.

I seem to making a habit of posting about theatre trips! Went to the National Theatre in London to see The Motive and the Cue. This was about the staging of Hamlet on Broadway in 1964, starring Richard Burton and directed by John Gielgud. It was really about the way the two clashed during 25 days of rehearsals - Gielgud's interpretation was very mannered and formal (he performed Hamlet 500 times!), and Burton's was fiery and emotional. They eventually found mutual respect. Directed by Sam Mendez, and starring Mark Gatiss as Gielgud, Tuppence Middleton as Liz Taylor and Johnny Flynn superbly as Burton. https://www.nationaltheatre.org.uk/productions/the-motive-and-the-cue/ https://en.wikipedia.org/wiki/Mark_Gatiss https://en.wikipedia.org/wiki/Tuppence_Middleton https://en.wikipedia.org/wiki/Johnny_Flynn What is interesting is that Flynn is the same age as Burton was in 1964, and Gatiss at 56 is almost the same age as Gielgud, who was 60 in '64. Likewise Middleton - Liz Taylor was 32 and Middleton is 36. So the ages of the main characters were very true to life. If you want to see what the Broadway play with Burton was like, YouTube is your friend

It is summed up in the last sentence: "I’ll choose magic, if only it didn’t come at such costs". And that sums it up - everything Dyson is a major investment. About the most affordable, and something I bought for MrsS, was a Dyson Supersonic hair dryer. It is still not cheap, but is is quiet, powerful and light. But would I spend three times that for a Dyson vacuum cleaner? Well no. I've just fixed our twenty year old Sebo with a new mains lead from eBay (the old one was chewed), and some duct tape over a hole in the base. It does the job, and the green thing is to keep it going until is really does keel over.

Here is an interesting figure The bottom axis is in kPa-cm. Atmospheric pressure is 100kPa. Let's say that we use a shoulder washer that goes into the ceramic insulator 0.5mm, so the overall arcing distance is 1mm, or 0.1cm. So we are interested in 100 x 0.1 = 10 on the horizontal axis. That says that the breakdown voltage is about 5kV - so we should be OK? Well no. Those curves (Townshend curves) are taken between two parallel plates, so an ideal measurement arrangement - the result of a very careful experiment. The case of a small diameter screw thread, which has voltage stresses from each thread peak reduces the breakdown voltage significantly. And it is uncontrolled - tiny bits of conducting swarf and other grot possible too. So an 0.5mm insertion into the ceramic is getting marginal for 500V. Increasing the insertion to 1.5mm gives an arc gap of 3mm (0.3cm), giving a (ideal, parallel plate) breakdown voltage of about 10kV. Even if this was degraded by a somewhat outrageous factor of 10 (1kV), we are still safe at 500V. Which is the basis for using shoulder washers that are as long as reasonably possible

because the OD of the washer extension is larger in diameter than the hole in the bracket and PCB, assuming they are nominal clearance holes for the fixing screws.

Found the spec sheet in my T2 parts folder - looks like I used 7721-3PPSG . That has an extension of 3.81mm (1/8") and that clearly worked. Again Mouser - they have 11,500 of them in stock.

You have that right - the T2 has some fearsome voltages knocking around - and detail for everything is the name of the game. To make the umbilicals connecting the power supply to the amp chassis took 8 hours solid work. That is typical of the length of time needed to not only make it work, but continue working as the months and years go by.

Regarding transistor mounting. I'm thinking back a looong time to when I built mine. I used steel screws, because I could not get enough torque on plastic screws (I use a torque screwdriver and read the data here https://www.onsemi.com/pub/Collateral/AN1040-D.PDF ). But the trick is to use the AAVID long penetration washers. You need enough length to go through the TO220 tab, and penetrate most of the way through the 4171G insulator. Now the problem is that the thickness of the tab is extremely widely specified - somewhere between 0.5mm and 1.39mm. I've done a straw poll of TO220 devices I have, and the vast majority are between 1.25mm and 1.3mm thick. My 4171G insulators are actually 2mm thick (at the top end of the tolerance; they are nominally 1.778mm (0.07") +/- 0.254mm (0.1"). So mine are towards the top end of the tolerance band. Anyhow, it looks like the AAVID 7721-13NG (Mouser has 8,000 of them) is the man for the job. I can't find the remainder of the ones I bought to check, but I think I used those. The extension is between 2.71mm and 3.26mm. You need to check your tab and insulator dimensions, but under most circumstances the shoulder washer will go through the TO220 tab and most of the way through the 4171G. If the tolerance stack goes against you, that shoulder washer might actually protrude from the bottom of the 4171G. If that is the case you absolutely must trim the end shorter. Otherwise you won't make thermal contact between the transistor and the heatsink. That will enable you to use steel screws and nuts (don't forget the lockwasher!). Oh - and you absolutely must use heatsink compound! Craig