Craig Sawyers

Well something is clearly different between his first T2 to his second. Any idea what he should check to find out?

OK - frequency has gone down (not too surprising since C has gone up) and amplitude has gone up a bit. The issue in my mind is that a gross instability around the feedback loop usually builds up to a rail to rail oscillation, whereas this is almost sinusoidal and well below the peak-peak of what this amp is capable of. Next line of attack - cascode circuits are notorious for self oscillation, which would probably limit the amplitude. So first look for differences in layout from one channel to the other - particularly (a) the position of R86 and R87 to U1 and U2. The position and routing of R6/C2 and R5/C1/R92. If there are differences between L and R - and a few cm of track might be enough - they might be significant enough to cause this. Not saying this is the cause - just working the options.

Mine is the original - no idea what the issue number was. Kevin might have that data. There have been various iterations since then

Getting a particular T2 stable can be a bit of a game. The problem arises from the fact that the feedback trace is quite long, physically. It was less long in the original Stax T2 because it was more compact (and as a result ran incendiary hot). Anyhow, the feedback trace has to get all the way from the output tube's anodes/plates all the way back to the input tube's cathodes. Mine used to hoot too - you need to adjust the 15pF value in small increments both upwards and downwards, and possibly add one or both 2.2pF caps, and again be prepared to tweak the value. While looking for oscillation and its frequency. Once it is stable, do a frequency response sweep and look for a response peak - if you find one continue adjusting those caps until it is critically damped. It is interesting to note that 15pF and 100k gives a dominant pole at ~100kHz whereas the oscillation is at 685kHz, which implies that there is a secondary feedback loop, possibly inductively coupling into the feedback trace. I have a vague recollection that I cut a trace and re-routed in some way, or changed the position of the upper feedback resistor, but I'd have to tear my T2 apart to find out what I did.

Yeesh. Last time I looked at this, maybe ten years ago, a 1956 bottle was around £700 - which was waaaay outside my price bracket. They seem to be even more outrageous now. For a superb real-world Glenfarclas at very good price, have a look at Glenfarclas 105 cask strength. Gorgeous stuff. Around UKP50 a bottle.

For something really special, Glenfarclas do a Family Casks range, from which you can buy a bottle from the age of your birth. http://glenfarclas.com/whisky/the-family-casks/ They are probably way outside your price range (mine too), but worth dropping them a mail and finding out.

If it is oscillating you'll find it everywhere. You'll need an oscilloscope to find out though.

One channel isn't oscillating at some high frequency?

Either a battery, or one of the many current sources? Stax block diagram.docx

I initially thought this was a joke - but no. Pay for a cocktail with a cucumber http://gulfnews.com/guides/going-out/restaurants/pay-with-a-cucumber-at-these-35-dubai-venues-on-may-17-1.2024849

An FG502 will do the lot, including sweep (you need to put a sweep signal up the VCF input). It goes from 0.1Hz to 11MHz, square, triangle, sine. http://w140.com/tekwiki/wiki/FG502 . Ebay has one 252934875917 for $25 with no bids yet. To make it work, you need a TM5xx power frame, like the TM501 122498573980 currently $49.99 with no bids yet. Or a TM503 with three slots (so you have some expansion space for other units (eg the RG501 ramp generator to complement the VCF sweep of the FG502) 361964662469 for $40 with no bids yet.

Depends on what your measurement requirements are. Do you need the square/triangle/sine capability of a function generator? Or is a low distortion sine more important (a function generator produces an approximate sine)? Manual set frequency and output level, or auto sweep (and hence linear or logarithmic sweep?). Then there are arbitrary waveform generators (AWG's) where you program them to produce any waveform you like. Whether a stand-alone box, or a PC-based generator again depends on what you need it for. Personally, I have a bit of a mix. For ppm level low distortion a Tek SG505. A Tek FG502 function generator. For high output an ancient HP 209A (see http://kenrockwell.com/audio/hp/209a.htm#perf ) and the workhorse is a Gould J3B.

^That was a fine and truly scary cold war movie. Limited nuclear exchange, president believed dead in helicopter crash in the blast, warmonger vice president takes over and scrambles a B52, which passes the point of no return. Must watch again. "By Dawn's Early Light", 1990. Stellar cast (including James Earl Jones, Martin Landau, Rip Torn) and of course Powers Boothe, RIP.

Have a truly great day!

Result!

Can't remember which one. I probably reported it somewhere in the bowels of this thread. But I definitely only replaced the blown one. Hasn't missed a beat since (around six years).

I had an early problem of this sort that turned out to be a J79 had blown. That was possibly the last gasp of collateral damage from fake C3675's. But that particular J79 took about a year to go pop.

Could be worse - she could be smitten by a Nissan Cube - that car the designers at Nissan decided to get the ugly out of their systems in a single shot. It looks dreadful from any angle.

Happy birthday!

RIP Geoffrey Bayldon http://www.bbc.co.uk/news/entertainment-arts-39885577 a British Actor, age 93 Catweazle was one of those must watch series from my pre-teen years. But he was also Q in Casino Royale and a number of other movies.

No idea. But since the police have found him I suspect that even if it is, it won't be there for long.

Way back in December I set the UK police system on the trail of this scam merchant, who was targetting US and other nationality buyers for high ticket audio items, getting the money, and sending no goods. He seemed to have been operating for years. Anyhow, I have just had a call from West Mercia Police asking me to confirm what my recollection was of his modus operandum. We chatted for a while, and I wished her good luck in finding the guy. "Oh - we know precisely who he is" So the system works - they have the bastard!

"altered cognition" - wow. Whatever caused that I badly don't want. Hope it improves Reks.

From http://www.magiclx521.com/epages/17940394.sf/en_GB/?ObjectPath=/Shops/17940394/Products/"afi USB"/SubProducts/"afi USB" which equates to about $1600 for the single input version or about $2100 for the four input version http://www.magiclx521.com/epages/17940394.sf/en_GB/?ObjectPath=/Shops/17940394/Products/"afis %26 USB"/SubProducts/"afis %26 USB" That takes either the three fibres, two RJ45 and a Toslink. If I was going this way I'd probably go for the one input version. The magic521 guy is interesting. As well as the Linkwitz kits, and supporting electonics, he's a commercial airline pilot! And yes - his business is in Germany.