Craig Sawyers

Maxwell rules OK

Shelly - hope you're having a great time!

I used those back in the dim and distant when using a metal turning lathe, either to make a feature for a tailstock centre, or prior to drilling a centre hole. I'd forgotten about them until now, and must get a few sizes for my drill press. To use such a lathe now I'd have to take a remedial course - too many decades have passed.

Check. Took maybe ten hours or more to completely stuff the amp board. Then another two or three to stuff the power supply. Hell, it must have taken a day or more just to purchase all the components - even with KG's excellent BOM. Probably another six hours plus to make the umbilicals. Add a bunch of time to wire the chassis to the boards. Then 20 to 40 hours to track down the counterfeit 2SC3765's and do a major re-build of the main heatsinks. I reckon 40 hours plus to build this sucker - when you know what you're doing. And that was with KG's chassis kit and boards. Then the same amount of time again to fault-find (yeah - I was unlucky with crap transistors. And happen to have a curve tracer to diagnose the problem and know how to use it). The equivalent in other areas of endeavour would be to chose an Aston Martin or a V12 Jag as your first car to rebuild and restore. And before you ask - yes I have restored my V12 Jag (but that cost **a lot** more than the T2, and took two years). I have a *very* understanding wife And it is lethal (as are all electrostatic headphone amps) - in the T2 some parts have way upwards of 1100V from one place to another, and enough current available to stop your heart .

FWIW our SAS (the sort of equivalent of SEALS) carried out a daytime raid on the terrorist occupation of the Iranian Embassy in London in 1980. All but one of the terrorists were killed during the raid, and only one of the 19 hostages. Summary is here http://en.wikipedia.org/wiki/Iranian_Embassy_Siege FWIW part two, my cousin Douglas (now 60-odd and retired) was either a member of the SBS (Special Boat Service) or the Royal Marine Commandos. He has some hairy stories to tell about active service, and last saw action in the Falklands. Now wears two support shoes because his ankles are knackered (through running everywhere with a full pack) and two hearing aides (from spending too long "next to things that go bang"). The nastiest episode was training in resisting interrogation that he volunteered for at the SAS training camp in Hereford. Two weeks of everything they could throw at him, starting with being released onto Dartmoor in October wearing only prisoner orange, and to evade capture. After five days on the run, cold and hungry, when he was captured hiding in a pigsty he thought "Relief - a feeling that lasted for about ten seconds" and "The only thing was that they did not hit you as hard as a real interrogator". After the training, everyone got four weeks off to recover, both physically and mentally.

Sorry 'bout the random repeat. Too much booze - hic. You've sure picked a toughie to build as a first major project! You need the Gerber files to send to a board house. Kevin ought to commernt here abuot what he specified. But standard is FR4, 1oz copper, 1.6mm thick. All you need to do is specify what primaries you want, and Paul will wind according to your spec. Bear in mind that 110V is usually 60Hz, so you ought to specify that too. Also, I guess that you want two windings that you either connect in series or parallel. I'm getting worried - to build the T2 you ought not be asking questions like that. It is difficult to build, demands someone who knows what they are doing, and is highly lethal if you don't know what you are doing Are you sure that you want to tackle this as a first project?

Jeez. That brings it home big time. Hats off, Grawk. I was working in London at the time, and travelling home through the Underground (tube) was very odd. I was working at University College, and the department prof came in and said "You're not going to believe this, but a plane has just gone into the WTC". No more work got done that day - we were all watching it happen on the web. All the major buildings in London had been evacuated, because we had no idea whether we were a target that day too. Everyone on the Underground was absolutely silent and just kind of staring into space. Deeply surreal.

Now *that* is interesting! So if we go for a 10K resistor, and use the Texas Z204 (with 0.4" lead spacing) the only thing missing is the 6R34. But - looking at the Charcroft site I find the equivalent document http://www.charcroft.com/site/pdf/data/aug2009/Charcroft.S.Series.Is4.09.pdf So I guess that all branded manufacturers use the same Vishay stock and then trim. I shall go back to Charcroft and ask; pity they did not volunteer the information straight off

I'm sure that is the case - for sure they would have fought like hell. I would certainly like to think that the chapter is closed, but I have a horrible feeling that worse is to come. Hey - I don't want to piss on the parade - I hope he rots in hell for all eternity. That bastard masterminded so many terrorist atrocities worldwide over the years http://en.wikipedia.org/wiki/Timeline_of_al-Qaeda_attacks he deserves the worst that can be meted out in whatever afterlife he has ended up in.

Thanks for the heads up - I changed ISP's when the one I used to be with (Hotchilli.com ) had a server crash and failed to recover the folder containg images. Staggering incompetence I'll find the images and upload them again - and then post the link.

I only wish they'd captured the bastard alive. That would have been much more demoralising for Al-Quaida, with him banged up in Guantanamo, or in some dank CIA bunker - whereas with him dead they have a martyr. Remember those sons of bitches bombed the shit out of London too (in 2005) with bombs on the Underground and on a London bus. Then they tried again two weeks after the first attack, but fortunately were incompetent enough that the bombs did not detonate, or only went phut.

Problem is that the higest value in z-foil of any description is 50k - so even a 10k version of the attenuator is missing the 169k. Upping the attenuator resistance just makes the availability of z-foils worse. I suspect that <50k is due to the combination of resistive material and the complexity of the metal pattern, and it does seem a hard limit for z-foil.

Check the T2 thread - chapter and verse in there. Counterfeit ones came via Dalbani in the UK. They replaced them without any quibble.

Check.

If you have a poke around on the T2 thread, I got under the skin of the battery while diagnosing multiple faults (caused by Chinese counterfeit 2SC3675's), including modelling it to work out the strategy for adjusting the original circuit's two pots. KG has updated and upgraded the circuit to get rid of the LED chain and JFET, but the operating principle is the same. In brief: Q4/Q5 are a long tailed pair that compare 10V from the reference with the voltage set on RV2. Q6/Q7 are DC level shifters to keep Q4, Q5 and Q8 inside the VceBR voltage at which they blow up. Q8 is a Widlar current mirror. This has a very high impedance, and is there to increase the gain of the long tailed pair - standard practice in IC's and high quality discrete designs. As you adjust RV1, the current through Q4 and Q5 is forced to be equal by the current mirror - so both increase in step. The output voltage is taken from Q8B - which is electrically equivalent to taking it from the collector of Q5 if we disregard the level shifter.

Hokay - I got some numbers from Charcroft. Note that 6R34 and 169K are not available, since Vishay do not supply untrimmed stock to cover those values. The costs below refer to the VSMP series http://www.charcroft.com/site/pdf/data/Charcroft.VSMP.04.09.Is4.pdf and the SCAR series http://www.charcroft.com/site/pdf/data/Charcroft.SCAR.04.09.Is2.pdf both in 2512 size. Tolerance is 1%, and MOQ is 10 off each value. Tax at 20% would have to be added too. Delivery is around 10-12 weeks. 255R to 16K9, £9.88 each 38K3, £10.52 each 82K5, £11.16 each The 1206 size VSMP are cheaper, but restricted to <25K 255R to 3K65, £6.57 6k04 to 16K9, £8.30 That puts the total cost (including tax) for a stereo attenuator using 2512 size at £360, or balanced at twice that. The 6R34 and 196K would have to come from elsewhere. The 1206 option is cheaper at £235 for stereo, but the 6R34, 38K3, 82K5 and 169K would have be alternative resistors. Multiply by whatever factor is appropriate for local currencies. What is the interest in this level of crazyness? Either on list or via PM.

Yeah - we can be a feisty bunch for sure, but I concur with deep's second paragraph.

Dickens' Martin Chuzzlewit on the Kindle

Well it is actually three days - Thursday, first empty garage and coat of expoxy floor paint. Friday second coat. Today first coat of masonary paint on the cinderblock (breezeblock in the UK) walls. All preparatory to moving all my woodworking gear from the cupboard-sized garden shed to the garage - and then getting on with some serious cabinet making. Knackered. Compensating by drinking - hic.

Local Oxfordshire brew called Dr Hexter's Healer. And very good too, being chased by an unholy amount of sherry, looking forward to some Australian red with the lamb - and I'll see where I get to from there later on. Could be liqueuer of some description or a single malt. Or both

OK - Charcroft said that they had good stock on the untrimmed Vishay 1206 Z-foil. I've just mailed them to ask for the quote to include 1206 too. Larger physical size resistors would have a lead time. After talking to them, it turns out that a major driver of cost is tolerance - so I've asked for 1% - the 1% ones that I have measured are all better than 0.1% (0.009dB nominal, not counting statistics. Even if you do, it will be a rootN thing. So maximum number of resistors = 17, so the maximum error due to 0.1% tolerance is <0.04dB. At -128dB, so who cares.

Good man! It sure is a helluva first (part one of two) episode for this series.

I've been working with some z-foils as part of another project - free issued by the company I'm working with on this one. Very interesting. I've been using both SM and leaded versions. These are nominally 1% tolerance, but actually measure better than 0.1% (ie better than my Fluke 87V can resolve) - which is good. These came from Charcroft, from whom I am still awaiting a quote for the attenuator resistors. The SM ones have the resistance value printed on the top of the expoxy case. The leaded ones have absolutely no markings at all - the only way to check value is with a DVM. I must admit it is a bit daunting to look at a very small pile of resistors and think of the monetary value of them....

I think that Kevin has made the board as flexible as possible for widest resistor choice. Regarding what resistors, I absolutely agree that the super-expensive ones will probably only be justified with equally high quality amps. Such as the T2 and KG Blowtorch clone to name two. So regular few cent metal film resistors are probably just hunky dory for the majority of applications. FWIW I've put myself in for two built ones and four bare boards - and I expect the built ones will be made with the resistors in the BOM - ie regular metal film. I will probably do something moderately crazy with the other four for the T2 or similar.