livewire Posted February 1, 2011 Report Posted February 1, 2011 One of those jobs that floats when you drop it in the toilet? <j/k>
kevin gilmore Posted February 7, 2011 Report Posted February 7, 2011 more fine work by kerry http://gilmore.chem.northwestern.edu/BlueHawaii-AB-T2-Servo-v1-0.zip
Lil Knight Posted February 8, 2011 Report Posted February 8, 2011 I'm going to do a small round of the new revised boards, so if anyone is interested, just let me know. This is done with Doctor Gilmore's permission. A friend of mine is running his own factory that can make PCBs. My last experience with the KGSSHV boards was excellent. I'm going to pick up the boards on my own. For 2 sets of PCB, price is $245/ea. 5 sets is $195/ea, 10 sets is $155. Plus shipping, plus fee. That's almost the same price like last time but we only need 10 people for the round. Keep in mind that you have to do the chassis work on your own this time because Doctor Gilmore won't do that tedious job again. Right now 2 sets are already spoken for. I'm hoping we can reach at least 5 sets. Also, if anyone is interested, I might be able to help with the back and front panels by acrylic or aluminum. Finish is brushed ,plain or glossy (not really sure about this, will ask my friend again to make sure). Laser engraving and CNC are available. Thickness is up to 15mm. Some samples 1 2 3 4 Custom power transformers can be done but I don't think I will take up that job because of the heavy weight.
Pars Posted February 8, 2011 Report Posted February 8, 2011 The problem is that Mosfet self oscillation is bewlideringly prone to both precise layout almost at the millimeter level, exactly where the bypassing is in relation to the transistor, and the gm of the transistors. There is a rather wide tolerance in gm, so perhaps an unlucky batch with high gm might be a trigger. There is an excellent Renesas apps note (simply called "Power Mos Fet Application Note" - 57 pages) which covers more Mosfet death mechanisms than I ever knew existed, parasitic self oscillation being only one. Maybe there could be some interaction with the input tubes which might explain the noisyness with some tubes that both you and Inu have mentioned. I don't have any stock of beads, so I'll go with the resistor and keep the value the same as for the J79. Interesting that I found this on a search (and I've even read it before, but didn't recall all the details). On a dynafet I am building, I have been having oscillation problems with 2SJ76/77 but more probably the 2SK213/214s. These have gate stoppers of 47 ohms, but this seems to be too low. 750 ohms sounds awfully high though. I was thinking more in terms of 100 ohms, but tried 120 ohm and while better has not completely stopped it (but much better). Maybe I'll try going up this high. Biased in the 75-150mA range.
Craig Sawyers Posted February 16, 2011 Report Posted February 16, 2011 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
Kerry Posted February 19, 2011 Report Posted February 19, 2011 (edited) With my keen eye for reading subtle meaning from a post, I've guessed that you're not too happy with your ISP Edited February 19, 2011 by Kerry
Fitz Posted February 19, 2011 Report Posted February 19, 2011 Don't hold back, tell us how you really feel.
spritzer Posted February 26, 2011 Author Report Posted February 26, 2011 My PSU is finally taking shape but I also bought some K216's from Dalbani and I suspect most of them are fakes: Sorry for the crappy picture. Most of them are like the ones on the left with only the 4 on the right looking authentic.
Lil Knight Posted February 26, 2011 Report Posted February 26, 2011 That burns. I have a source that sells the K216s really cheap and they all have the long legs like the ones on the right. Thinking of getting a bag of 100. Is it confirmed that the ones on the left are fake (and the right ones are genuine) ?
blubliss Posted February 26, 2011 Report Posted February 26, 2011 One of my transformers bit the dust, now I am T2less for awhile.
spritzer Posted February 27, 2011 Author Report Posted February 27, 2011 What's with the forum software. This thread just now kicked into the "View New Content"... That burns. I have a source that sells the K216s really cheap and they all have the long legs like the ones on the right. Thinking of getting a bag of 100. Is it confirmed that the ones on the left are fake (and the right ones are genuine) ? It looks like they are fakes but I've yet to have them tested. One of my transformers bit the dust, now I am T2less for awhile. What happened? Looks like I'm in the same boat as my HV transformers weren't made correctly... From Bdent: What do you think? Those could be genuine but the markings aren't something I've seen before. The packaging looks genuine though.
kevin gilmore Posted February 27, 2011 Report Posted February 27, 2011 center tap on the high voltage windings is optional. 1
blubliss Posted February 27, 2011 Report Posted February 27, 2011 What happened? Looks like I'm in the same boat as my HV transformers weren't made correctly... Well, I had it on all day over the weekend and as I was listening the sound started to get soft. I thought it was the song until something popped, and then the driver tubes started to turn off. I turned it off and smelled burned stuff and after I opened the PS I saw the plastic on top of one HV transformer was melted in a small area. I tested the leads and the 485 was shorted. PS voltages are still fine so nothing wrong there. I'll have to check the current draw which I never did before. The SumR guy said it needs to be below 80ma.
spritzer Posted February 28, 2011 Author Report Posted February 28, 2011 On the spec sheet you got from SumR it states the temp rise at full load. Mine are 37.5°C which makes them burning hot to say the least... I think it might be a good idea to swap these transformers out for a much higher rated unit.
Kerry Posted February 28, 2011 Report Posted February 28, 2011 I was just about to pull together the requirements for the transformers. I'd be looking for a significantly lower temperature rise. The last transfomer I ordered from SumR, we were able to get them made with a 22°C rise at full load. For the three transformers what were you thinking (power wise) for each winding? I think the most significant power is pulled by the Neg. 500V supply at about 33mA (per channel per LTSpice). I'd like to keep them as cool as possible so 4x seemed reasonable, which would put it around 133mA (assuming LTSpice is right). Here's the specs that Kevin gave so it's pretty close. craig asked that i publish the info on the transformers, should you decide to have them made elsewhere... high voltage transformer 2 are needed diameter 3.5 inches height 1.7 inches you can actually go up to 2.5 inches high, and slightly wider full load voltage---- regulation--- Iac--- off load 475 --- 15.04 --- .13 --- 546.4 285 --- 10.53 --- .06 --- 315 75 --- 10.6 --- .06 --- 82.9 filament transformer diameter 3.5 height 1.6 30 --- 13 --- .5 --- 33.9 Center tapped 6.3 --- 14.29 --- 1.5 --- 7.2 6.3 --- 14.29 --- 1.5 --- 7.2 6.3 --- 14.29 --- 4.0 --- 7.2 6.3 --- 14.29 --- 4.0 --- 7.2 Richard at SumR can take these and beef up the windings to accomodate the lower temp rise, but we need to make sure the size doesn't exceed 2.5" tall by about 3.5" wide (not sure on max width). I'd like to try to get the same specs as you if you are reordering.
spritzer Posted February 28, 2011 Author Report Posted February 28, 2011 First I'm going to check to see if the PSU works at all and if the heat is an issue for me. Being in Iceland does have its good points from time to time, most notably cheap AC...
jcx Posted March 1, 2011 Report Posted March 1, 2011 xfmr manufacturer's idea of "reasonable" Bmax and definition of "saturation" can be a little scary - I've seen pri excitation currrent jump 5-10x for a 20% high line V compliance test if you're specing custom try to get them to use the next larger core size
Craig Sawyers Posted March 2, 2011 Report Posted March 2, 2011 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.
Kerry Posted March 2, 2011 Report Posted March 2, 2011 (edited) Welcome back Great information! What are the diameters / heights of your transformers. I'll keep those limits in mind as I put the specs together for SumR. Thanks. Edited March 2, 2011 by Kerry
spritzer Posted March 2, 2011 Author Report Posted March 2, 2011 The known issue with the original T2 was indeed the transformers and they run very, very hot. Kevin did look into that but I'm way too tired to remember what his findings were...
Craig Sawyers Posted March 2, 2011 Report Posted March 2, 2011 Welcome back Great information! What are the diameters / heights of your transformers. I'll keep those limits in mind as I put the specs together for SumR. Thanks. 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.
blubliss Posted March 4, 2011 Report Posted March 4, 2011 My T2 lives again, SumR got me a new transformer quickly. Kerry, let us know if you come up with something different, please. Dropped in a quad of Amperex 6922 and they sound excellent!
kevin gilmore Posted March 4, 2011 Report Posted March 4, 2011 over the years i have seen bunches of torroid transformers burn up. And not just on audio gear. If we could find a video of them being wound, you would see all the issues that can cause trouble. You spec the transformers as best you can, and hope the manufacturer has a clue. But i know of one well known manufacturer that still to this day has very little clue what they are doing.
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