aussievintage Posted November 23, 2020 Share Posted November 23, 2020 18 minutes ago, xlr8or said: Just adding that this is also highly dependent on the heater supply if it's regulated or unregulated. Tolerance specification on the 9-pin 12AU7 and 12AX7 mini is +/- 5%. If it's heated at 6.3volts it's about +/- 0.3volts. If it's heated at 12 .6volts it's double the value. This also infers that the higher heater voltage would see less change for a 20volt AC mains increase. Rectifers running at 5volts +/- 0.25 volts are another story. Yes, if regulated it does not matter anyway. Sheets I checked say +/- 10% not 5 % 1 Link to comment Share on other sites More sharing options...
xlr8or Posted November 23, 2020 Share Posted November 23, 2020 19 minutes ago, aussievintage said: Yes, if regulated it does not matter anyway. Sheets I checked say +/- 10% not 5 % Bugger me the later ones even say 20%. Here is the I was going off for 5%. 1 Link to comment Share on other sites More sharing options...
muon* Posted November 23, 2020 Share Posted November 23, 2020 I like all operating points as close to where the designer intended, and that means a mains as close as possible to what the power transformer expects. If I had the dosh I'd have one of those power plant thingies that make sure It's dead on. 2 Link to comment Share on other sites More sharing options...
xlr8or Posted November 23, 2020 Share Posted November 23, 2020 (edited) 21 minutes ago, muon* said: I like all operating points as close to where the designer intended, and that means a mains as close as possible to what the power transformer expects. If I had the dosh I'd have one of those power plant thingies that make sure It's dead on. Ian, just get yourself one of those big Yambashi variacs second hand and you're in business. Alternatively, here is another solution from Korea with 10volt AC mains steps. Edited November 23, 2020 by xlr8or 1 Link to comment Share on other sites More sharing options...
muon* Posted November 23, 2020 Share Posted November 23, 2020 (edited) 18 minutes ago, xlr8or said: Ian, just get yourself one of those big Yambashi variacs second hand and you're in business. Alternatively, here is another solution from Korea with 10volt AC mains steps. Thought about variacs, but they are not meant to operate long term as far as I understand. But then that's just my perception of them, due to a brush connection *shrug* I was getting a solid 250vac from the wall here for a couple of years, annoyed me to no end, but about a year ago I noticed it had changed and has been within 3vac +/- of 240vac 24/7 ever since A happy amp is a happy..........amp owner Edited November 23, 2020 by muon* 3 Link to comment Share on other sites More sharing options...
aussievintage Posted November 23, 2020 Share Posted November 23, 2020 9 hours ago, muon* said: I was getting a solid 250vac from the wall here for a couple of years, annoyed me to no end, but about a year ago I noticed it had changed and has been within 3vac +/- of 240vac 24/7 ever since and noting Australian standard voltage is 230 Vac , not 240 1 Link to comment Share on other sites More sharing options...
kelossus Posted November 23, 2020 Share Posted November 23, 2020 1 hour ago, aussievintage said: and noting Australian standard voltage is 230 Vac , not 240 They changed the standard on paper but that's all. 2 Link to comment Share on other sites More sharing options...
aussievintage Posted November 23, 2020 Share Posted November 23, 2020 4 minutes ago, kelossus said: They changed the standard on paper but that's all. Yeah I know, it was said a bit tongue in cheek. It does enable overseas products to be sold as suitable for us, when at 250 they will struggle though. 2 Link to comment Share on other sites More sharing options...
Gazer01 Posted November 25, 2020 Author Share Posted November 25, 2020 On 07/11/2020 at 7:38 AM, Bisguittin said: You are a very bad influence @xlr8or. I've already placed Telefunken ECC802S in the 12AU7 spots. Hi @Bisguittin just a noob question. So I can roll any type/model of preamp tube for replacing 12au7 or 12ax7 without worrying about the bias or anything? Cheers. Link to comment Share on other sites More sharing options...
Bisguittin Posted November 25, 2020 Share Posted November 25, 2020 Correct regarding my unit, and very highly likely in yours. The only thing you have to worry about is colossal damage to your hip pocket! 2 Link to comment Share on other sites More sharing options...
benno21 Posted December 28, 2020 Share Posted December 28, 2020 (edited) Hi there, I am a customer of Mingda since I bought a MC-34 AB back in 2009. I still remember my bargaining with Suena regarding the price, who as I do understand still works with that company . Later on I purchased a MC-300 pre from the factory. I still possess both and can say that the built quality is good, the schematics used ok and there is no concern regarding safety. That said,I modified both to iron out little quirks but still consider them worth purchasing, particular if you plan to optimize them. If you invest some money into NOS tubes and replace some of the caps you will get good sonic improvements. Another country which produces excellent amplifiers nearby is Vietnam. The other half of my tube equipment originated from Thivanlabs. Excellent built quality, unique product design at a price level extremely competitive to Mingda products. That said I enjoy the in my view unbeatable combination of the Mingda MC-300 preamp with EML 300 Mash tubes and lightly modified with the Swan 211 (Thivanlabs). Edited December 28, 2020 by benno21 files attached 5 1 Link to comment Share on other sites More sharing options...
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