Craig Sawyers

Well, what are we talking - $30 each? So $120 for four. And that replaces four EL34's at $120 for a Winged C quad from Parts Connexion, plus

20mA standing current through the output devices - wow! Twice the T2 value. WOOF... Or reduce R39. My 2sc4686a have a low voltage gain of 25, or about 30 at ~600V. Conditon for operation is that the base current of Q23 plus the equal currents through Q20 is the current through R39. So say 10uA through each half of Q2 = 20uA plus 5mA/30=200uA about. So R39 would have to be halved in value (in the T2 the current through R39 is 100uA). Or chose the operating voltage of Q16/17 bases to double the voltage across R39 and so double the current through R39, and keep value at 62k. Just saves another transistor is all. Which all goes into the heatsinks. I make that an additional 9W dissipation for each sink. Sounds like a helluva good project to me. And although the power MOSFET's are expensive, they are certainly going to be less expensive than the tubes and teflon sockets, and also saves the cost of a third transformer for the heaters.

Have a look at the PSU Designer line that is the transformer secondary rms current (listed usually I(T1), scroll along to the rms column). You will see that it is a factor of several times (around three) greater than DC current. That factor is precisely the same as that given using Schade's graphical method. The relevant graphs are here Electronic Transformers - Rectifiers with Capacitor-Input Filters . The one you want is called Figure 52 on that web page, top graph line. For a full wave rectifier, "n" = 1 (Schade's method also takes care of voltage multipliers, which have different integer values of n)

How many lines did Schwarzenegger actually have in the movie? "I'll be back", "Get out", "Fuck you, asshole" are the instantly memorable ones. Whatever, it was not a big speaking part I actually think Terminator 2 is by far the better movie, Wayne's World notwithstanding

Terminator. For the first time in years. Not a bad movie.

I was just trying to get a rise, Doug I succeeded....

I must admit, as an Englishman (well Geordie) that Scotland has reputedly the worst food. They have the highest incidence of heart attacks and the lowest life expectency in the British Isles. They have a particularly heart congesting option at the fish and chip shop - battered and deep fried Mars Bar. For those who don't know what a Mars Bar is - it is a sort of chocolate filling, with a caramel top, all inside a chocolate coat. About 3 x 1 x 1 inch. And very good they are in moderation - but battered and then deep fried is a Scottish speciality, to be taken on the way home from the pub. And now I'm buckling up to come under fire from the Scots on the forum

As they would say in my home city of Newcastle - "You looking for a Byker kiss?"

Is that a slot at the bottom rear? It isn't a transmission line perhaps? DSP speaker control (including DSP room EQ) was pioneered at Essex University in Malcolm Hawkesford's group. In the late 80's and early 90's. The guy who was doing this as part of his PhD is called Richard Bews, founder of LFD audio Lfd - amplification phono stages analogue interconnects digital interconnects loudspeaker cables

Ah - so that is why the judges chose your cake as the winner - they were on a solvent high! Better than ground up pot

Yes - here it is http://www.alliedelec.com/Images/Products/Datasheets/BM/GC_ELECTRONICS/796-2068.PDF . The red stuff is 1700V/mil, and the black is 3800V/mil.

Ah - it is Red-X corona dope. A super high voltage conformal coating. The Mr Fixit for balky 7000 series Tek DC restoration and HT supplies (some of which run at 21kV). In the olden days, Tek used a black version of this on the ceramic strips holding the voltage multiplier components.

Yup. Forgot that one. My T2 ones have insulation barriers between all windings - including the heater ones because two of them float at -500V. Although the wire insulation is OK in principle, a combination of winding tension, pressure high points, and then friction as the transformer heats and cools makes it last the square root of bugger all time in practice. Same principle is at play with interwinding screens - they absolutely need double insulation barriers on either side otherwise the thermal/friction/tension will always end up with shorts to windings.

That sounds absolutely typical, Justin. Either they overheat, have the wrong voltage under load, or hum. Or all three. I get mine from Paul Houlden, who used to be TD of Avel Lindberg, then of Holden and Fisher, the founder of Chameleon, and has designed toroidal transformers for most high end audio and pro-audio manufacturers (Krell etc). I work with him to develop a spec, and then he hand delivers them. There are three of his in my T2.

Surprising how often transformers are underrated in professionally designed equipment. The calculation is simple for something like a heater transformer, since the secondary rms current rating is just the heater current. But with capacitor-filtered DC, there is a factor to be taken into account as a result of the short pulse-like nature of the charging current. This was originally analyzed by Schade in 1943 ("Analysis of Rectifier Operation", Proc IRE July 1943, 341-361) and resulted in a series of normalised graphical relations, which are still useful to this day. But whatever method of calculation you use (for example freeware PSU Designer II from PSUD2 ), the rms current rating of the transformer needs to be typically 2 to 4 times higher than the dc current drain. The exact factor depends on the capacitor size, the transformer effective DC resistance, the DC current, and the mains frequency. Incidentally, isn't DAG (Deflocculated Acheson Graphite) conductive? Or is there another meaning to DAG that I've missed?

Um - if they are volatile, they aren't going to stick to anything. And they are going to come off anyway even if you air dry it on a sunny day outside. And with the extract hood going they aren't going to give me a solvent high

The other real killer in pro-audio gear, which is usually fan cooled and sucks in large amounts of air, is the smoke that is used for stage effects. That puts a layer of mildly corrosive goop all over the inside that buggers circuit boards and puts a conductive layer over everything.

And that looks truly spectacular. Looks like the the amp equivalent of a custom car job. MMMM. Inu's powder coated T2 looks great - and his coater managed to get right in to the heatsink fins. I did my KG triode chassis with black crackle finish - which you can get from specialist suppliers of car restoration accessories. Sprays on and looks just like flat black, but as it dries (in the domestic oven - shhh, don't tell - the wife was out...) it crackles.

You will note that I actually said "If you are still concerned, you can go over the leads, package entry and PCB pads with a conformal coating pen - a bit like solder resist, apart from the fact that you can solder through this stuff if you need to do a repair" So what precisely is your point? Specifc RTV (Room Temperature Vulcanising) formulations - and there are very many - have an application on very high voltage stuff, or on multi kV voltage multipliers in TV's and oscillosopes, but looks like a pig's breakfast on something like an electrostatic headphone amp. Nail polish is based on a chemical concoction of agressive solvents (like toluene, butyl acetate, ethyl acetate etc), different from one manufacturer to another, that I would let nowhere near circuit board solder resist, let alone passive components, or even semiconductor packages. I also have no idea what it's high voltage insulation properties are - I seriously doubt that anyone has measured it, and the manufacturers for sure won't know. Back when I was 16 I used it for masking simple self-etched circuit boards, but that is about the only electronic use for it IMNSHO. If you are going to insulate package lead outs and PCB pads - which is fine and dandy - , use the correct material for the job - it is called conformal coating - and is available from any decent supplier (Mouser, Farnell, RS components, etc etc etc). Available in a spray can, a can of liquid for use with a spray gun, or as a pen for local application.

Great cake. MMM cake. Image shack provided cake, and also offered me an advertising screen offering me shag buddies, and a selection of windows-like pop-ups offering porn downloads. MMM cake.

Heavens - lets just knock the whole idea of DIY on the head, why not? After all, what was good for the death of Heathkit ought to be good enough for the death of all the DIY projects on Head Case. Let's get a little perspective here, please! And rely on a seasoned electronics professional like KG to know his stuff.

MMM - cake.

Creepage and clearance is all to do with product safety. Where the regulations apply is when a hazardous condition can arise through breakdown or shorts - for example around a power transformer, either conventional or switching, or in common-mode inductors in power line filters for example. This is particularly important because power lines are subject to high voltage transients through industrial users, power line fault handling, and environmental disturbance (lightning, solar weather etc). Creepage and clearance has to take these conditions into account. Internal parts in which electrical breakdown does not give rise to an external hazard condition (such as via the chassis, exposed connectors or cabling) are not covered. This thinking is well considered in the European Low Voltage Directive Electrical Safety: Low Voltage Directive (LVD) - Electrical engineering - Enterprise and Industry In any event, the lead spacing between the wide part of the pins on a TO220 varies considerably depending on the device. Specification and caliper measurement on three devices rated at 800-900V have minimum interlead spacing between 1.02mm (0.040") and 1.35mm (0.053"). The highest voltage device, a 2SA4686A with 1200V Vceo, has 1.65mm (0.065"). In fact there is a lot of evidence that semiconductor manufacturers know about all this, and chose a lead frame that takes device voltage handling into account. Air breakdown is 3kV/mm, and so these devices are all comfortably derated, with the absolute maximum device voltage being between a third and a quarter of the air breakdown voltage. If you are still concerned, you can go over the leads, package entry and PCB pads with a conformal coating pen - a bit like solder resist, apart from the fact that you can solder through this stuff if you need to do a repair.

Those tubes are 50W handling (so those monoblocks must be the thick end of 100W each). The downside is that the tubes are $2k a pair.

The neat thing that I've done in the past in products I've developed (mainly mil stuff) is to have the panel engraved after either powder coating or anodising. The engraving can either be left as it is, or filled with colour - or a range of different colours. Much more robust than silk screening. One of the old timers from Tektronix was telling me the way they developed the lettering for the old tubed 500 series was to have a load of panels done in different ways (engraved and filled, screen printed etc) and stuck them to the floor in Tektronix's entrance hall. Employees were required to walk on them when they passed to pick the most robust. The original choice was engraved and colour filled. They then moved to silk screening once they had a process that also passed the walking test.