Craig Sawyers

Thanks Kevin. Kind of confirms my ball park numbers. I guess if I were designing this from scratch I'd put quite a bit more current down the long tailed pair to ensure enough margin (power dissipation in the 2SA1486's is not a problem), or make the output transistor a darlington to reduce base current.

OK, having been listening to the BH for a month or so, I'm girding my loins for the repair of the T2. Since the death mechanism for me seems to be second breakdown in Q23 (the 2SC3675 in the battery) I was trying to get to grips with the design of the battery. Now no-one else has had problems with Q23 in this location, so it is probably a batch issue - the batch that I bought was just too marginal on SOA. I realise however that I have an imperfect understanding of the operation. I'll go through what I've worked out, so anyone can chime in. First consider Q16/17, which is a long tailed pair. Nominally the base voltages should be very close to each other. The base of Q16 is fed by constant current source Q22 and resistor R42. The base of Q17 is fed via a resistor chain with RV1 in the middle. Looking at the resistor values, with RV1 set at the R32 end, Q17 base voltage (WRT the top rail) is 6.2V. Similarly, with RV2 set to mid track, the equation for an FET constant current source with Idss about 6mA is a drain current of 0.28mA. Flowing through 22k resistor R42 this produces 6.2V at the base of Q16 - precisely the same as that at Q17. So all well so far. The current through R39 is (6.2V - Vbe)/62k = 5.6V/62k = 90uA, which is shared between Q16 and Q17 - so 45uA through each transistor. Q18 and Q19 are simply voltage sharing - the bases are connected to the halfway point of the battery, so Q16/17 and Q18/19 only see half the battery voltage - important since these are 600V parts. Q20 is a perfectly standard Widlar current mirror load, which boosts the gain of the long tailed pair Q16/17. Problem is that Q23, the 2SC3675 has an hFE of around 50. Its collector current is determined by 5mA constant current source Q30. So the base current of Q23 is 100uA. And here is nub - there does not appear to be enough current in the collectors of Q16/17 (45uA through each) to drive 100uA into the base of Q23. So what am I missing?

Yeah - cheap those resistors aren't. But very, very good. And the 5mm pitch means you need to lay out the board to suit.

At our school in the NE of England in the late '60s the general rule was that is you were duff at football (soccer), you were by definition duff at any sport. I disliked the sport then, and dislike it still. My asshole PE teacher found no inconsistency in my being a member of the school swimming team (which he did not run) and his soccer prejudice. Took me until my early 20's to throw off the sports duffer mindset he ingrained into me, and take up running, at which I have enjoyed for the last 32 years.

A strange and warped hunchback with a face like derelict industry. Like a cowboy's armpit. Like an abandoned dockside crane. Like a desiccated prune

Go for Dale RN60D, Spritzer - as near to a perfect resistor as you are likely to get and still not take out a second mortgage

You'd be surprised how few resistor types are non magnetic. Vishay bulk foil, old fashioned Allen Bradley carbon composition, original Holco, and Dale mil-spec are all non-magnetic. Highly thought of and expensive resistors like Shinkoh and Audio Note tantalum, and RC55 precision film are all magnetic. As are all regular film types I have tried, like the Xicon. I'm not convinced that the magnetic characteristic is a determining factor in sound quality - there are many other resistor parameters that are more likely to influence sound quality.

A wizened old fart with a face like an old turnip. Like a lonely walnut. Like a grieving cod. Like a thumped plum. Like a neglected radish

Last night watched 13 days. I was 7 when these events played out, and we came a hairs breadth from global nuclear incineration.

I didn't realise that wrestling was such a big thing in the US until I started reading the novels by John Irving. Most of his books have large bits of disguised autobiography in them - being set in New Hampshire, often with an estranged parent somewhere, and with quite a bit about wrestling (Irving used to wrestle). His latest, Last Night in Twisted River, actually has one of the characters as an author who writes novels with disguised autobiography in them - a book by Irving, with an Irving-like novelist as a character. I just love Irving's books.

Thanks everone! She's actually still at acting school doing "Acting for Radio, Film and Television" - so she should get the opportunity to do much more than radio, although her real passion is for stage acting. My wife and I are a bit bewildered where precisely she gets her looks from.

Daughter won lead part in a radio play to be showcased to agents and producers, so she is buzzing at the moment. I've registered her stage name as domain ellasawyers.com as an extra present for Christmas. [ATTACH=CONFIG]3958[/ATTACH]

Just been reading about this. Inflation is 230 million percent. Once it got to banknotes of trillions, they took 27 zeros off. Then later they took another 12 zeros off. Currently around 400 zimbabwean dollars per US dollar. For the next few minutes anyway.

Wow! That is damned impressive, Stretch! How much is that worth in real money?

The only thing I could mention is something I'm a bit anal about. The capacitor charging current from the bridge diodes is pulse like. The current drawn from the capacitors is pretty smooth. So it is always a good idea to isolate them in the tracking - in other words that the diodes connect individually to the capacitor terminals, and the output connections also connect separately to the capacitor terminals. Otherwise the pulsing current flow from the diodes flows in part of the output tracks and can introduce unnecessary PSU noise. Similar things can be done on the ground side as well to prevent the same pulsed currents from getting into the output grounds - this used to be called the "Calrec rectangle" after its adoption by the microphone company.

Just length and number of teeth per inch. For fine dovetailing you want something with an 8" blade, filed rip tooth since cutting dovetails is a ripping rather than a cross-cutting operation; most cheapo saws bewilderingly come filed crosscut. For small stuff like jewellery boxes you really want 20 teeth per inch. For larger stuff like dresser drawers I'd go as high as 15 teeth per inch - but getting that started in the cut takes a bit of practice. The nicest handles are open or "pistol grip" rather than closed. Steer clear of the so-called "gents" saw, which has a round handle and has no good control as a result. There are several sources for really fine dovetail saws. I use Dovetail Saw - Pax Range from Thomas Flinn & Co Saw and Hand Tools Manufacturers Lie Nielsen are also good, and Rob Cosman has made his own (although it is punishingly expensive). I used the Cosman at a woodwork demo last year, and it really is stunning. Some saws are what is called "progressive pitch" where the teeth are very fine near the tip, and get coarser towards the handle to overcome the starting problem (Flinn Garlick and Lie Nielsen do these too). Rob's has two discrete pitches - 22tpi at the tip to get started and then 15tpi for the remainder. His theory is that you really want a coarse pitch to do the cut, since the faster you cut the more accurate it tends to be. Most fine makers ensure that there is only a few thou of set to the teeth - you want a minimum clearance just to prevent the blade from binding and no more. Too much set and the blade can wander in the cut. Then there is the entirely opposite approach of using a japanese style saw. These are used on the pull stroke and take a bit of practice to get used to. Super-fine kerf, so could be worth a bash for jewellery box joints. You want the Ikedame, which is the dovetail variety. A whole lot cheaper than traditional western pattern back saws. I use both types depending on the work. I also use the Hassunme crosscut and ripcut saws for cutting panels (although I last used them for trimming the bottom off our bedroom doors when we recently had a new carpet fitted!).

My dentist is good at extractions - extracting money from my wallet in unholy amounts that is. Drives around in a huge BMW land cruiser and lives near Henley-on-Thames in a high-end village called Christmas Common.

That is great news! Truly great news.

Follow the method set out by Rob Cosman. Apart from being a fine hand tool craftsman, he has got blisteringly fast demos on YouTube doing a through dovetail joint in two minutes, and half lap dovetails in seven minutes. Google his name - you'll quickly get the drift. Buy his various DVD's - covers tuning and sharpening your dovetail back saw etc etc. Use his method of using hockey tape to bind your coping saw which gives it a whole lot better grip in your hand. With true deference to grawk, a dovetail jig gives really boring joints with wide roots to the tails. They have to be wide because of stength of the router bits. And you have yet another woodworking operation accompanied to the scream of a router. With a finely tuned saw you can produce tails limited only by the width of your saw kerf. I've got nowt against routers and power tools - I have two big and chunky deWalt half inch chuck ones and a lightweight Bosch, plus bandsaw and planer/thicknesser. But there is nothing more satisfying than doing a finely hand crafted dovetail or mortice and tenon joint without power tools. Because I'm a bit of a hand tool freak, I have an expanding collection of back saws. Most recent addition arrived today - a Diston apple wood handled dovetail back saw made sometime between 1896 and 1917 (from the rivet design). Once I joint it and resharpen it rip tooth it will be a fine and practical saw.

To lighten things up a little - sheep have the same problem. The Australian sheep farmers have a term for Vicky's cat problem - they call the adherent material "dingle berries". Thinking of sheep, do a Tou Tube search for "Family Guy Sheep Shearing" for perhaps the most twisted take on shearing a sheep out there.

So much trouble and sadness on the list at the moment. My heart goes out to all.

You've got to be kidding me. Is yours a particularly hairy-butted breed?

That figures, Reks

It is a sobering fact that the only reason we are here is as a direct result that our forebears survived whatever life threw at them - famine, pestilence, persecution, war etc, going back over the centuries.