Craig Sawyers

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.

It sure is. I sent KG a chunk of Lignum Vitae, and he did the business. There are some detailed pics he took before shipping it way back in this thread somewhere. A real source of joy - just waxed it to bring out the grain.

Try Permissible RMS Voltage Between the Legs of a TO220 package? for the answer. And your font is small because you used Times New Roman. New Romans must have had good eyesight.

They are Pearl tube coolers. Main aim is to even out and reduce envelope temperature - increases tube life by a factor of two - but they do have a damping effect too. Corrugated and blackened copper held on with high temperature O-rings. Important with four rather expensive Mullard xf4 original EL34's. Got them from Parts Connexion.

Here's a couple of pics with the T2 where it lives in the corner of our bedroom (and that was an interesting conversation, trust me ). [ATTACH=CONFIG]4217[/ATTACH] [ATTACH=CONFIG]4216[/ATTACH] Also measured the amp heatsink temperature after 8 hours = 48C (118F). The power supply was quite a bit cooler than that.

Well first off - don't believe for one minute that my build of the T2 was without problems! But the shoulder washers wasn't one of them. The only thing to watch is that these are one thou larger in bush diameter than a regular TO220 bush. So they go into some transistors real easy, and in others they are pretty tight (technically an interference fit) - but they do go in with some persuasion - depends on where in the tolerance band the bushes and transistor holes lie.

It is the Aavid 7721-3PPSG. Bush length is 3.18mm (1/8"). Wall thickness is 0.36mm (14 thou) and the material is 40% glass filled polyphenylene suphide, which has a dielectric strength of 385V/thou - so 14 thou = 5.4kV. I've used these exclusively on the T2, and we're talking 50 devices mounted to grounded heatsinks this way, without any difficulty.

I've never found a plastic screw (and I tried a few different types on my T2 build) that will take anything like the recommended torque for a TO220 (around 1.1Nm, 8-10 inlb). The best reference for semiconductor mounting I've come across is Onsemi's AN1040D http://www.onsemi.com/pub/Collateral/AN1040-D.PDF . I ended up with a long Aavid bush that went most of the way through the 2mm alumina insulator, and then used steel fastenings.

Whatever you do, ask them about masking the areas where the fixing bolts go so all the chassis components electrically connect together. You really need that for safety, and at the very least not to feel that tell-tale tingling feeling when you touch a floating piece of chassis. You *can* remove the coating where the screws are afterwards (Dremel), but any coating worth a damn is tough, and this is a pain in the ass given how many fixing bolts there are. They may ask you to do this, in which case you need to find out what sort of tape they recommend to do the masking. I discovered this gotcha decades ago after I bought a second had copper vapour laser (at work). All the laser head chassis components were thick powder coated, and not electrically connected. There was so much high power interference getting out the chassis seams that I got an rf burn. I was not impressed.

Yup. Solid rules those Yeah - I had a couple. Which weren't really enough for setting up a T2, so I went on an eBay raid. So now got 4 8060A's, an 8024B and an 87V. Put 1mm jacks on the test points on the tube side of the board and made up some 4mm to 1mm test leads. So I can set the batteries up by just taking the top plate off and plugging straight in. Put a ground wire on the board so another pair of meters go from ground to the stax jack. Switching those between DC and AC allows the noise voltage to be measured durning final battery tweaking.

Interesting comment, Inu. Could you expand on that please?

Here's something interesting. The BH seems to take quite a while after turning on to come on song - around an hour or maybe more. But the T2 wakes up very fast - a minute or two after the HT relay clicks in and it struts its stuff. Have any of the others with completed beasts noticed this?

That is a classic. If you haven't done that at least once, you haven't lived! Depending on the Fluke, you are likely only to have fried the input protection. There are a couple standard fuses, a couple of fusible resistors (which you have to get from Fluke), four thermistors (cheap standard parts) and some transistors wired as diodes. Some or all may have gone to heaven. You can tell from the way I rattled that off without looking at a schematic that I've been where you are now. The lesson I've learnt the hard way on several occasions is don't test stuff when tired.

Result! Happened twice to me, once with a pen and once with an HP calculator. Bought replacements - at which point the original escaped from the bowels of the cabin. I'm sure there are black holes whose purpose is to screw with your mind. It is where all my odd socks and allen keys go.

I haven't read any Lovecraft for a very long time. That is my wake up call to read or re-read a few of his very disturbing books.

Yes - A bit like Hichhiker's Guide "Every time I press one of these black controls, labelled in black on a black background, a little black light lights up black to let me know I've done it. " The only relief is the glow of the tubes and the awesome lignum vitae knob

Just for the record, there were three mods to the power supply and amp: (1) The power supply mod developed by Kevin and Inu to make it stable (2) Adding precautionary 750 ohm resistors in series with the gates of all K216's (3) Adding 5pF 1kV caps (I used ceramic, Inu used mica) across the 100k feedback resistors. That was also an Inu mod. (1) and (3) are essential IMHO. (2) is discretionary - these resistors were not present in the original from examination of the photos. It has already been said - this sucker runs real hot. Once it has been on for a few hours the heatsinks, front panel and top plate are toasty.

Wife came home to the new walkman on the kitched table [ATTACH=CONFIG]4210[/ATTACH]

Omygod. I'm speechless and breathless - I've really heard nothing to compare with this. I could witter on about speed and clarity, and the tendency to listen to things far too loud because there is zero listening fatigue. Looks guys - I have a BH, and bloody good it is too. But KG's recreation of the T2 is simply in another league. OK - the right channel has noticeably hiss, but that is because I need to frig with the battery voltage a bit on that channel. What I need to do is stop listening for long enough to pull the lid off again. Mind you - it served up a bit of a fright. I'd had the thing on/off/on/off etc as I was messing around trying various cures for the 650kHz problem with no mishaps. Put all the covers on, heaters came up, but when the HT came on the fuse blew. WTF??? Tore covers back off to find the gremlin. There wasn't one - the 2AT fuse I had in the IEC was clearly not man for the inrush job (6.3A in there now) - but it waited until I'd put the gadzillions of screws in before it gave up the ghost.

At the moment a used Edicron quad that I had lying around that still measures pretty good. I've a good set of original Mullards that will probably end up in there, or I might get another set of Winged C (I've a set of those in the BH, and they sound very good indeed) and keep the Mullards for Sunday Best. I've got a set of Pearl tube coolers too - evening out variation in the envelope temperature and reducing it double tube life - something that was researched by Mullard etc back in the 50's. 6DJ8's are Mullard's pilfered from a wrecked Tektronix scope that measure right on the button.

WHOOOO! Squared! Second channel now operating. Adjusting those pots is pretty trivial having worked out what they actually do - and having halfway decent silicon in there. I'm going to award myself a run, some lunch, and then put the front panel on and have a listen

WHOOOOOO! First channel operating!!! RV1 and RV2 do exactly what the simulation and spreadsheet says, as is my suggested way of adjustment. Outputs sitting at -4.5V and batteries at 743V. I can probably get the output offset lower than that, but I'll now concentrate on the other channel for a while.

Way to go! That is another corner turned

Wierd factoid - I've missed every episode of this. But the general opinion (including critical acclaim in the UK) is so high that I have just got to get a set of DVD's of this and catch up.