Craig Sawyers

The ones that Paul wound for me were 93mm OD x 55mm height for the HT ones and 98mm OD x 69mm height for the LT one. All windings had a double thickness insulation barrier between each mainly as a precaution, but essential on the LT transformer since the EL34 heaters sit at -500V. They were centre epoxy filled with a single bolt hole, and the top of the centre fill was below the top of the windings. I used 65mm long dome headed steel bolts with plain washer, lock washer and nut to fix them. If they were conventional fixings with rubber washers and a steel disc, you'd have to think carefully if they would fit or not into the case height.

Problem is that they are now paying Clarkson, Hammond and May so much that they have no money left over for big stunts like the Reliant Robin space shuttle launch. Clarkson earned £1m from his general BBC contract and another £819k from Top Gear last year. Add that to the half million plus each that Hammond and May get, for a total salary bill of near enough £3m. Nothing like Kelsey Grammer's $1.6m per episode of Frasier, but more than enough to cramp they style of a UK motoring show.

Well guys and gals - I'm back! With a new and shiney ISP called ICUK http://www.icukhosting.co.uk/ . The transformer question is interesting. Hot is OK, provided that it is within the design ratings of the insulation used. Mine were designed to a specification of 42C temperature rise at full load - so 62C with an ambient of 20C. I've confirmed that with a thermocouple. That temperature is conservative, considering that the design maximum temperature is 120C. Anyone for fried eggs? The most thermally stressed transformer is the HT one with all three secondaries connected. Based on power supply modelling, the RMS transformer currents are: 475V, 0.19A 285V, 0.08A 75V, 0.1A The problem arises because of the spike-like current that the rectifiers deliver to the storage caps. The RMS/Average ratio is higher than you might imagine, so 66mA (average) taken out of the 500V supply caps needs an rms feed of 190mA from the transformer (for a 30-ohm effective winding resistance; lower resistance is worse becasue the charging spikes get shorter). All of which calls for 120VA in total. A lower-power transformer will of course still be OK provided the core doesn't start to saturate and the regulation is OK - all that will happen is that it runs even hotter - which is generally OK provided the insulation standards are good enough. I'd suggest that a failure in the transformer is due to failure of insulation, or a pressure point from a pigtail solder joint. One thing that has to be borne in mind is that cycling a transformer puts the internals under repeated mechanical stress as it heats up and cools down. So any weakness is found out in due course. My 120VA transformers are at the limit of what will physically fit in the chassis. To use really underrated transformers which run significantly cooler would require mounting the transformers externally to the T2. Mine are not SUMR - they were custom designed by Paul Houlden in the UK, who used to do (and still does) transformers for high end manufacturers like Krell. I recall somewhere hearing that the original T2 transformers used to burn out, and were replaced with more conservatively rated ones by Stax.

Happy birthday Dan!

Duur - late... But hope you had a good one!

Beans on toast. Sad ass dinner for one while wife is playing tennis. But I LIKE beans on toast - so why am I bitching?

Double birthday - double congratulations

I'm going to sound like a real dork - but I read the thread topic as "Official Hockney Thread", as in David Hockney the artist. Honestly. Time for (another) Scotch, I think. Thought it was a bit of a wierd topic on Head Case

Apologies for anyone trying to access files on the T2 from my website. My crap ISP suffered a server crash , and it has taken them over three weeks to restore a modicum of my website - but currently still missing the critical folder in which all the interesting files on audio and other technologies are stored . Needless to say I have a request for quote out to half a dozen small-business focused ISP's so I can move away from hotchilli.com. They used to be great ten years ago - small and hungry. But they sold out to a private equity outfit , who have transferred all their support to India. Now I have no problem at all with Indian support - but when there is no option at all now to talk to someone in the UK, and they are bungling incompetents to boot, it is clearly time to jump ship. I'll let you know when the ensuing chaos of this decision settles down again

Hey - have a great one

Have a great one. I'm drinking your health right now.

I was just talking to my brother-in-law Steve about the Clarkson/Mexico international incident, and Clarkson's beautiful not-apology. We got onto insults of the same sort - like the "cheese-eating surrender monkeys" by Groundskeeper Willie about the French that was in the Simpsons back in '95. Anyway, Steve pointed out that you get an interesting result is you type "Famous French Victories" into Google and then hit "I'm feeling lucky". Enjoy

Buzzing transformers are caused by incorrect manufacture in the first place. The only way to shut one up is to decouple it from the chassis big time. Assuming for the moment that it is a toroid, first take it out. Then make a vey thick layer of RTV - maybe 3/8" or so - and gently seat the transformer onto it. Make sure it does not squeeze out. When that has set somewhat, make a similar layer on the top and set the clamping washer on it. Put the bolt through to keep it lined up. When everything has set, nip the bolt up. The transformer is now vibration isolated from the chassis via two thick resilient layers. A similar thing can also be done with EI core transformers of course, but it would need some extra thought about how to deal with the bolt fixings. Using rubber grommets instead might work fine and is quick to try out. Precautions - try to chose an RTV that will cope with a transformer temperature of 60C.

Also screws up heater voltage too - but that is common with most amps. Problem is that DC stabilised heater supplies are always inefficient. You need around twice the VA rating on the heater transformer to do DC.

I didn't realise that they were dipole woofers. I'm part way through a dipole subwoofer project to support the bottom end of the ESL57's. Using Shiva-X2 drivers http://www.diycable.com/main/default.php which I chose because there is no chuffing noise from the rear of the speaker ever at a scary 2" p-p excursion.

I can't claim that long bush idea was mine - Inu tracked those down as part of his T2 build. He used plastic screws as well, but the fact that the bush goes almost all the way through the alumina insulator means that steel fasteners work perfectly. Only thing to watch is that although the outer diameter of the bush *should* fit in a TO220 hole, tolerance stack up sometimes means that it is a very tight interference fit. Feel the force, kgsshv buider, feel the force. Believe it will go in and it will.

Now this I like Cheers Tyll

I've established that the UK supplier is http://www.highendworkshop.co.uk/ , run by a really interesting guy called Mark Dolbear. His price for a new pair of black Lambda pads is £25 including tax and shipping, which looks like a deal.

All this talk about rotten foam (my old low bias SR-lambda's have gone that way) has got me thinking about replacements. They sound quite a bit more forward as compared with the SR-007/2 so cloth/foam might act as a taming influence. Are all current replacement pads capable of being fitted to the 1986 vintage lambda? Superficially current production looks the same.....calling Spritzer, calling Spritzer...

Berkshire, eh? Happy birthday from a Geordie living in Oxfordshire

Here's an excellent article about Barrie Gilbert http://www.ieee.org/portal/cms_docs_societies/sscs/PrintEditions/200710.pdf

How about something based on a Gilbert Cell? This is a truly wonderful circuit that can be used for everything from four-quadrant multipliers, phase detectors, ultra-high bandwidth amplifiers etc. Developed by Barrie Gilbert while working for Tektronix, and the basis of may of Tek's custom high bandwidth hybrid and integrated circuit amplifiers. Still active and working now for Analog Devices in his 70's (AD set up a lab in Beaverton just so they could poach Gilbert from Tek). http://en.wikipedia.org/wiki/Gilbert_cell

Slight delay in evaluating the anti-650kHz mods - I've devloped a head cold (from my wife; thanks Carole!), so I've gone as deaf as a post because my sinuses are rebelling. Once I've got over this damned thing I'll get back on track and do some sonic evaluation and measurements.

I'm using an old Tek 475A with a P6106A 10x probe. All you need to do is put the probe anywhere near the output tubes (ie not physically connected to anything at all) and you can pick up several tenths of a volt to several volts at 650kHz. Then connecting between either + or - output and ground you measure around 10V p-p at 650kHz. The 475A is definitely overspecced for this, since it is a 250MHz bandwidth scope. The detail of this particular problem might have to do with the precise choice of resistors - I think Inu used PRP's throughout, and he doesn't seem to have the oscillation problem to anything like the same extent as I did. I used Xicor metal films.

I've tested the DALE ones that KG specified in the BOM on my RF bridge, and they are exceptionally good, measuring 80k even at 200MHz with an effective parallel capacitance (actually of course a series inductance) of 0.2pF. That is bewilderingly good performance for a 3W power resistor. The Mills ones are wire wound IIRC, but non-inductive?