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#1
Posted to rec.audio.tubes
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211 A2 amp
Hi All.
I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick |
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#2
Posted to rec.audio.tubes
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211 A2 amp
"Nick Gorham" wrote in message ... Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. Hi Nick. Lovely project:-) Just when RAT seems to have reached an all-time low - karamba - someone like you posts details of a project like your 211 and restores our faith in human nature and endevour:-)) Some test results would be of interest, as and when. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. And by the sound of it, you were not disappointed:;-) There transformers are very good indeed. I have a magnificient set of Sowter potted OPTs for a KT88 PPP amp, which is looming up. Meanwhile, today I put the finishing touches to a 30W EL34 mononloc prototype. After discussions here, particularly with Patrick, I was keen to make an unconditionally stable amp, even at the risk of a slight deterioration in other parameters. Rock-steady into 0.22µF is sometimes not easy to obtain:-) It has THD of 0.05% at 1W, and 0.25% at 25W. Some square wave pics are shown at: http://www.kolumbus.fi/iain.churches...eWavePics.html Regards to all Iain |
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#3
Posted to rec.audio.tubes
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211 A2 amp
On Mar 28, 3:10*pm, Nick Gorham wrote:
Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick Nice work, Nick. You may come make the case for my next amp. Are you publishing a schematic? Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review |
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#4
Posted to rec.audio.tubes
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211 A2 amp
On 3ÔÂ28ÈÕ, ÏÂÎç11ʱ10·Ö, Nick Gorham wrote:
Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick Do you want access to China's massive pool of electronic manufacturers... but lack the time to contact suppliers, negotiate contracts, arrange shipping or monitor product quality? Don't worry - Let seriouswholesale deal with all that for you. *Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD / Audio, and Computer Accessories now by visiting the online wholesale catalog at seriouswholesale. com You'll have peace of mind thanks to the seriouswholesale Quality Control, 12-month Warranty on all products, and easy secure payment by credit card through Paypal. Selling on eBay or your own online store? Send products direct from our warehouse to your customers using our unique drop-shipping service. You can profit by selling hundreds of different products, without holding any of your own inventory! Any questions you have will be answered by the seriouswholesale English-speaking customer support team... Their aim is to make your China electronics importing business easier to run than ever before. Welcome to http://www.seriouswholesale.com. seriouswholesale - Buy from the source, profit without the hassle. - 12 Months Warranty - No minimum order restrictions - Drop-shipping with no additional fee - Pay by safely by PayPal seriouswholesale Wholesale Co., Ltd.: Chinas original and best online electronics wholesaler & drop-shipper: seriouswholesale. com |
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#5
Posted to rec.audio.tubes
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211 A2 amp
Hi,
What a nice amp! How does it sound? It is good to see some people building amps again. This is what this group is really all about. I have been working with the 2A3 myself, but want to move up in size. I've been thinking of the 211 or 845. Anyway, enjoy that amp! Oh, is that an old Hitachi Oscilloscope in the background? I had a house fire last September and lost all my test equipment. My scope was an older dual trace Hitachi that looked a lot like the one in your picture. Take care, Bill |
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#6
Posted to rec.audio.tubes
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211 A2 amp
wb wrote:
Hi, What a nice amp! How does it sound? It is good to see some people building amps again. This is what this group is really all about. I have been working with the 2A3 myself, but want to move up in size. I've been thinking of the 211 or 845. Anyway, enjoy that amp! Oh, is that an old Hitachi Oscilloscope in the background? I had a house fire last September and lost all my test equipment. My scope was an older dual trace Hitachi that looked a lot like the one in your picture. Take care, Bill Thanks. I am happy with the sound, a number of us are organising a valve/hifi/sad geek meeting next month, so I will hopefully get some second opinions then. The scope is a Gould, old but does the job, but I should gt a faster one sometime as I want to play with some DAC designs soon. -- Nick |
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#7
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Nick Gorham" wrote in message ... Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. Hi Nick. Lovely project:-) Just when RAT seems to have reached an all-time low - karamba - someone like you posts details of a project like your 211 and restores our faith in human nature and endevour:-)) Some test results would be of interest, as and when. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. And by the sound of it, you were not disappointed:;-) There transformers are very good indeed. I have a magnificient set of Sowter potted OPTs for a KT88 PPP amp, which is looming up. Meanwhile, today I put the finishing touches to a 30W EL34 mononloc prototype. After discussions here, particularly with Patrick, I was keen to make an unconditionally stable amp, even at the risk of a slight deterioration in other parameters. Rock-steady into 0.22µF is sometimes not easy to obtain:-) Well, I don't think a tube amp of any kind using global NFB and which has been unconditionally stabilised is going to suffer "deterioration of other parameters", which presumably are imaging and "openess of sound", whatever that is. When you have a large amount of class A, wide open loop BW, and enough NFB to get Rout low enough, and THD below 0.05% at a few watts, generally there is better sound than if you removed the NFB, even with triode output tubes. A few AB tests I've conducted over the years have been a torture for the anti NFB fetishistas. Its preferable for peace that they consider some mild NFB as a means to allow tubes to sing like a choir of angels but with a gag tied around the mouths of the few inevitable choir members who can't sing in tune. Patrick Turner. It has THD of 0.05% at 1W, and 0.25% at 25W. Some square wave pics are shown at: http://www.kolumbus.fi/iain.churches...eWavePics.html Regards to all Iain |
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#9
Posted to rec.audio.tubes
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211 A2 amp
Nick Gorham wrote: Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick Good work Nick. Hmm, I guess you now know something about the appalling weight to power ratio of well made SET amps. Don't let it worry you, 211 make nice watts. I suppose you'd hope you'd never drop such an amp, lest the timber chassis turn into a mass of splinters. I'm currently completing a pair of 60W monos with 2 x 845 in parallel SET. I found steel was the only material suitable for such heavy chassis, and I had to place the PT on a separate chassis to make enough space on the amp chassis, and to keep the weight down. Each PT and OPT is potted, and uses a 71mm stack of 51 tongue E&I GOSS cores. There are 5 chokes per channel, using 25mm to 32mm stack x 25mm tongue. Its easier for someone to move 4 chassis all under 30kG than moving only two, each over 45 Kg. The Sowter trannies look nice. How about a full set of test results, Rout, bandwidth, THD with different loads, noise, etc... And what schematic have you got? The Copper Wire Producers Association and Amalgamated Ferrous Core Manufacturers Union will soon be sending a celebratory and congratulatory Certificate Of Wonderment ( COW ) your way soon. I tried to get them to just send a cheque instead, but they never replied. Patrick Turner. |
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#10
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Iain Churches wrote: "Nick Gorham" wrote in message ... Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. Hi Nick. Lovely project:-) Just when RAT seems to have reached an all-time low - karamba - someone like you posts details of a project like your 211 and restores our faith in human nature and endevour:-)) Some test results would be of interest, as and when. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. And by the sound of it, you were not disappointed:;-) There transformers are very good indeed. I have a magnificient set of Sowter potted OPTs for a KT88 PPP amp, which is looming up. Meanwhile, today I put the finishing touches to a 30W EL34 mononloc prototype. After discussions here, particularly with Patrick, I was keen to make an unconditionally stable amp, even at the risk of a slight deterioration in other parameters. Rock-steady into 0.22µF is sometimes not easy to obtain:-) Well, I don't think a tube amp of any kind using global NFB and which has been unconditionally stabilised is going to suffer "deterioration of other parameters", which presumably are imaging and "openess of sound", whatever that is. I increased the stability margin by several dB, and so with a little less NFB the THD was marginally higher. Regards to all Iain |
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#11
Posted to rec.audio.tubes
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211 A2 amp
"Nick Gorham" wrote in message ... Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick, when you have a moment, some pics of the innards would be of interest. Please also tell us about the Tentlabs heater module. Regards Iain |
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#12
Posted to rec.audio.tubes
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211 A2 amp
I said... Well, I don't think a tube amp of any kind using global NFB and which has been unconditionally stabilised is going to suffer "deterioration of other parameters", which presumably are imaging and "openess of sound", whatever that is. I increased the stability margin by several dB, and so with a little less NFB the THD was marginally higher. The best stability margin you can have is with no global NFB. Then as you add NFB, you can draw a plot of the margin of stability if you really must, and by the time you have say 30dB applied, and the test with 0.22uF across the output causes inevitable HF oscillations no matter what you do to the compensation networks, or, you get LF oscillations that cannot be cured with gain tweaker networks, then you have reached the point of maximal applied FB for that amp to get the wanted bandwidth say of 10Hz to 50kHz. Its possible to tweak open loop phase shift even further if you settle for less closed loop bandwidth but you shouldn't, because you'll end up with an amp with maybe 35dB NFB applied at say between 500Hz and 5kHz, and each side of the that the efectively applied NFB will reduce because of the reduction of OLG with networks. With such reductions of OLG, the reduction of distortion products at above 5kHz becomes less, and sound goes hard, most probably. 30dB of NFB was applied around a large number of amps back in the 1960s to get typical THD 0.05% at a dB below clip at 1kHz, R load only. So at 3 watts typical was 0.02%. Companies liked to take part in wars of Watts, and battles of THD to get sales. In my mind there is no need for such low THD/IMD figures simply because the products formed in class A working of tube amps is much more bearable than say the same amount but higher numbered H in a class B SS amp that has not been designed very well. In fact 0.1% THD in any SET amp at 3 watts is fine, because its all 2H, and IMD results are not as appalling as one might suspect. But I get samples of SET amps made by DIYers and some companies like Silk Amps from Thailand, and they have maybe 5% THD at 2 watts from a very poorly conceived circuit, and this is way too high. The use of a pair of KT88, KT90 or 6550 of 300B for the output stage means anode idle dissipation is naturally higher than lesser capable tubes such as EL34, 6L6, KT66, 6V6, EL84 etc, so therefore the class A PO before class AB action commences is higher. And if you ever draw a graph of the distortion against output voltage you'll see that THD is very low while the amp is in class A, and then it increases more rapidly above the A to AB threshold, but which really only need to handle transients such as drum beats and cannon shots. The maximum amount of class A available depends on the RLa-a load, anode dissipation, ie, Ea x Ia at idle, and maximum anode efficiency for class A which is about 45% for multigrids and up to about 30% for the same trioded or for 300B. More PO is available in A2. If you carefully read all my pages on load matching to triodes and beam tetrodes you will see what load values required for pure class A and how the load affects the maximum PO and balance between A and AB PO. And if anyone is allergic to NFB, then to get anywhere decent ENOUGH measurements that the best sound from tubes depends, they must use triodes and a high value RLa-a, say 12k with KT88 and Ea = 500V, Ia = 60mA per output tube, ( only with multi grids, not 300B ) This means they'll select a Hammond 1650P which has 6k6 : 4, 8, 16 ohms and they will never use the 8 and 16 ohm outlet config, and with 8 ohm speakers the tube RLa-a is 13.2k, and PO ALL class A. OPT winding losses become lower, as you increase speaker Z with a give outlet value. Then it will be found that no matter what tricks are played, the output stage has around 1% THD mainly 3H at a dB below clipping, with about 20 watts available. If more PO is wanted, halve RLa-a and use 4 output tubes. The 40 watts of pure class A will be sublime, but nobody bothers to waste so much electricity, and they back off the bias to 35mA even with only 2 output tubes. Then class A PO drops but 90% of what they listen to is covered by pure class A and the distortions rise only slightly for the class A region although its not unusual to get 2% THD or more with class AB at full PO. Suitable input/driver stages with low THD are shown at my website. At 3 watts in a 20 watt PP pure class A amp, expect 0.3%, and 0.15% in the 40 watter. Pure class A has THD dropping linearly with VO, not PO. The least THD should be where there is no RL connected, and the load line is a nearly horizontal line, and maximal Va occurs with almost no Ia change. But you will still see up to 1% THD just under clipping. The internally applied local NFB action within the triodes is maximal because gain is maximal. Things are a lot worse with tetrodes or pentodes used as such. The UL connection is a great help, but the CFB connection is better, and can give lower THD than triodes at the same PO, and maximal A1 PO is also greater. I have not tried the 211 in a PP circuit. Suppose Pda = 60 watts per tube. At max class efficiency of say 25%, expect 30 watts of pure class A, which is 948Vrms across the 30k OPT primary. The OPT is a devil to wind compared to making one for 6k, and to get the same wide BW from 10Hz to at least 50kHz. 845 under similar dissipation amounts would make 30% efficiency, and give 36 watts, but one can run them with Pda = 75 watts each and go into a little A2 and get 60 watts class A from a pair in either SE or PP. The PP load needs to be 24k, and the OPT is a difficult thing to wind to get the bandwidth expected today. Its possible that where the bandwidth is difficult to get, you have two OPT, one for below 1kHz, and the other cap coupled to the anodes for the above 1 kHz F. global NFB arrangements if used become fiddly. A circlotron with 845 could be done, but is entirely unecessary because Rout and THD/IMD is all low enough with the anode loaded tubes and no loop NFB at all. The 805 of some other high µ large triode may be suited to a circlotron because you need a lotta FB with 805. And you'd need a shirt and trouser load of driver voltage, which is bleedin difficult, wheras global NFB applied back to an input triode cathode is so much easier. Patrick Turner. Regards to all Iain |
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#13
Posted to rec.audio.tubes
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211 A2 amp
On 3ÔÂ28ÈÕ, ÏÂÎç11ʱ10·Ö, Nick Gorham wrote:
Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick Do you want access to China's massive pool of electronic manufacturers... but lack the time to contact suppliers, negotiate contracts, arrange shipping or monitor product quality? Don't worry - Let seriouswholesale deal with all that for you. *Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD / Audio, and Computer Accessories now by visiting the online wholesale catalog at seriouswholesale. com You'll have peace of mind thanks to the seriouswholesale Quality Control, 12-month Warranty on all products, and easy secure payment by credit card through Paypal. Selling on eBay or your own online store? Send products direct from our warehouse to your customers using our unique drop-shipping service. You can profit by selling hundreds of different products, without holding any of your own inventory! Any questions you have will be answered by the seriouswholesale English-speaking customer support team... Their aim is to make your China electronics importing business easier to run than ever before. Welcome to http://www.seriouswholesale.com. seriouswholesale - Buy from the source, profit without the hassle. - 12 Months Warranty - No minimum order restrictions - Drop-shipping with no additional fee - Pay by safely by PayPal seriouswholesale Wholesale Co., Ltd.: Chinas original and best online electronics wholesaler & drop-shipper: seriouswholesale. com |
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#14
Posted to rec.audio.tubes
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211 A2 amp
On 3ÔÂ28ÈÕ, ÏÂÎç11ʱ10·Ö, Nick Gorham wrote:
Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick Do you want access to China's massive pool of electronic manufacturers... but lack the time to contact suppliers, negotiate contracts, arrange shipping or monitor product quality? Don't worry - Let seriouswholesale deal with all that for you. *Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD / Audio, and Computer Accessories now by visiting the online wholesale catalog at seriouswholesale. com You'll have peace of mind thanks to the seriouswholesale Quality Control, 12-month Warranty on all products, and easy secure payment by credit card through Paypal. Selling on eBay or your own online store? Send products direct from our warehouse to your customers using our unique drop-shipping service. You can profit by selling hundreds of different products, without holding any of your own inventory! Any questions you have will be answered by the seriouswholesale English-speaking customer support team... Their aim is to make your China electronics importing business easier to run than ever before. Welcome to http://www.seriouswholesale.com. seriouswholesale - Buy from the source, profit without the hassle. - 12 Months Warranty - No minimum order restrictions - Drop-shipping with no additional fee - Pay by safely by PayPal seriouswholesale Wholesale Co., Ltd.: Chinas original and best online electronics wholesaler & drop-shipper: seriouswholesale. com |
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#15
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote:
"Nick Gorham" wrote in message ... Hi All. I finally finished the A2 211 amp I mentioned in some postings to Patrick some time ago, so I thought I would post a link to some images. http://www.lurcher.org/nick/images/211/ Sorry the quality of the images leave a lot to be desired as they were from a camera phone, but they give the general idea. I am very pleased with the sound it makes, Running in A2 seems to have a powerfull character about it, more so than the previous 211 amps I have built. I think I might try a similar idea with a 572b output next. All TX wound by Sowter, as I know Iain rates them very highly I thought I would give them a try. -- Nick, when you have a moment, some pics of the innards would be of interest. Please also tell us about the Tentlabs heater module. Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ The Tentlabs units are a nice and simple way of heating DHTs, AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I find with my open baffles and sitting position, anything over about 1mv of hum on the speaker terminals is audible. You can get more details from Guido's web site. -- Nick |
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#16
Posted to rec.audio.tubes
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211 A2 amp
"Nick Gorham" wrote in message ... Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ Hello Nick. Lovely job:-) I have sent the pics to a couple of chaps with whom I share a workshop. The Tentlabs units are a nice and simple way of heating DHTs, I asked about these, because, as I mentioned to you before I want very much to build a good SET and have been collecting info and ideas for a while now. AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I don't think that's obsessive. My own view is that the amp should be silent from the listening position. It is not too difficult to build a PP of say 50W which is totally silent EAS (ear against speaker) but SET is a totally different challenge. I find with my open baffles and sitting position, anything over about 1mv of hum on the speaker terminals is audible. Yes someone else, Andre I think, mentioned that fig some while ago. I have given up measuring SNR and now like to investigate the noise floor in µV. I think it tells one a lot more. By the way, your note at the link says: "At 1w the frequency response is 10hz to 37kHz at -3dB, 20hz to 24kHz at -3dB" Should this be 20Hz - 24kHz at -1dB ? My SET project folder is thickening out nicely. I shall be in touch when I am ready to take the first faultering steps:-) Look forward to some figs. Cheers Iain |
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#17
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Well, I don't think a tube amp of any kind using global NFB and which has been unconditionally stabilised is going to suffer "deterioration of other parameters", which presumably are imaging and "openess of sound", whatever that is. Iain said I increased the stability margin by several dB, and so with a little less NFB the THD was marginally higher. The best stability margin you can have is with no global NFB. Indeed but a little NFB does wonders for a PP amp I find. Then as you add NFB, you can draw a plot of the margin of stability if you really must, and by the time you have say 30dB applied, Never managed to get that far 26dB is my best:-) I usually check the response of the amp open loop, and then add a 10k pot for Rfb. I decrease the value until the amp starts to oscillate and then back off ten (or more) dB That's the empirical method I was shown as a lad. Is there a better way? and the test with 0.22uF across the output causes inevitable HF oscillations no matter what you do to the compensation networks, or, you get LF oscillations that cannot be cured with gain tweaker networks, then you have reached the point of maximal applied FB for that amp to get the wanted bandwidth say of 10Hz to 50kHz. Once I have got the Rfb sorted out, and replaced with a fixed R then I start to look at the stability into O/C and a cap. Once again, I use empirical methods, but the more you do it, the better you get at it:-) Its possible to tweak open loop phase shift even further if you settle for less closed loop bandwidth but you shouldn't, because you'll end up with an amp with maybe 35dB NFB applied at say between 500Hz and 5kHz, and each side of the that the efectively applied NFB will reduce because of the reduction of OLG with networks. With such reductions of OLG, the reduction of distortion products at above 5kHz becomes less, and sound goes hard, most probably. How does one go about tweaking the open loop phase shift? 30dB of NFB was applied around a large number of amps back in the 1960s to get typical THD 0.05% at a dB below clip at 1kHz, R load only. So at 3 watts typical was 0.02%. Companies liked to take part in wars of Watts, and battles of THD to get sales. These days many tube amps seem to have power quoted at 1% THD. In the 60s+70s 0.1% was more common. And if you ever draw a graph of the distortion against output voltage you'll see that THD is very low while the amp is in class A, and then it increases more rapidly above the A to AB threshold, but which really only need to handle transients such as drum beats and cannon shots. Yes I have done that, and also compared a KT88 Class A with a KT88 AB1 at various levels. I also plotted distortion against frequency at various levels. Now that's an eyeopener! Iain |
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#18
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote:
By the way, your note at the link says: "At 1w the frequency response is 10hz to 37kHz at -3dB, 20hz to 24kHz at -3dB" Should this be 20Hz - 24kHz at -1dB ? My SET project folder is thickening out nicely. I shall be in touch when I am ready to take the first faultering steps:-) Woops, you are right, fixed now. -- Nick |
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#19
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Nick Gorham" wrote in message ... Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ Hello Nick. Lovely job:-) I have sent the pics to a couple of chaps with whom I share a workshop. The Tentlabs units are a nice and simple way of heating DHTs, I asked about these, because, as I mentioned to you before I want very much to build a good SET and have been collecting info and ideas for a while now. AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I don't think that's obsessive. My own view is that the amp should be silent from the listening position. It is not too difficult to build a PP of say 50W which is totally silent EAS (ear against speaker) but SET is a totally different challenge. Why is SET a special challnge for noise? My 60W amps with a parallel pair of 845 with very little global FB pass the EAS test easily. At a metre, there is no indication they are switched on except visually. Initially, this was not the case with an un-potted PT crammed onto the same chassis as the audio circuitry. The power supplies are now separate from the audio amp chassis. the PT, OPT, and the two chokes for the choke input PS for dc heating of cathodes are all potted, and mechanically inaudible beyond 300mm. The EAS test is never quite what you say it could be for any amp. Just about all amps make some noise with EAS. Using headphones across the output soon tells you about amp noise. I find with my open baffles and sitting position, anything over about 1mv of hum on the speaker terminals is audible. Yes someone else, Andre I think, mentioned that fig some while ago. I have given up measuring SNR and now like to investigate the noise floor in µV. I think it tells one a lot more. I know a guy with TL12 Leak amps which he's trying to use with Lowther horns. Hum is his enemy, and he hasn't a clue how to reduce it. Quad-II don't hum with the Lowthers he says. By the way, your note at the link says: "At 1w the frequency response is 10hz to 37kHz at -3dB, 20hz to 24kHz at -3dB" Should this be 20Hz - 24kHz at -1dB ? My SET project folder is thickening out nicely. I shall be in touch when I am ready to take the first faultering steps:-) If anyone uses a pot to null the hum in a DHT using an AC source to the cathode, the best way to do the null adjustment is with a pair of headphones at the output. PP 2A3 can be quite hummy unless each OP tube has had its hum nulled in this way if it uses AC heating. The null with PP is better than with SE. and dc heating is always better for low noise. Patrick Turner Look forward to some figs. Cheers Iain |
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#20
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211 A2 amp
Iain Churches wrote: "Patrick Turner" wrote in message ... Well, I don't think a tube amp of any kind using global NFB and which has been unconditionally stabilised is going to suffer "deterioration of other parameters", which presumably are imaging and "openess of sound", whatever that is. Iain said I increased the stability margin by several dB, and so with a little less NFB the THD was marginally higher. The best stability margin you can have is with no global NFB. Indeed but a little NFB does wonders for a PP amp I find. Then as you add NFB, you can draw a plot of the margin of stability if you really must, and by the time you have say 30dB applied, Never managed to get that far 26dB is my best:-) I got 35dB max global NFB with the early version of 8585 which has about 12dB NFB in the output stage from the CFB connection while in class A where OP tube gain is maximal. I usually check the response of the amp open loop, and then add a 10k pot for Rfb. I decrease the value until the amp starts to oscillate and then back off ten (or more) dB That's the empirical method I was shown as a lad. Is there a better way? Its OK, but you are not changeing the OLG phase character to suit the wanted NFB, or the compo cap across the Rfb, or the gain step networks to reduce gain at extremes of F. There are actually about 5 things to be juggled, not just 1. After about 20 amp projects, and trying to see just what has to be done to get stablity good and bandwidth wide with global NFB, you'll get the hang, while appreciating the old fashioned empircals. and the test with 0.22uF across the output causes inevitable HF oscillations no matter what you do to the compensation networks, or, you get LF oscillations that cannot be cured with gain tweaker networks, then you have reached the point of maximal applied FB for that amp to get the wanted bandwidth say of 10Hz to 50kHz. Once I have got the Rfb sorted out, and replaced with a fixed R then I start to look at the stability into O/C and a cap. Once again, I use empirical methods, but the more you do it, the better you get at it:-) Exactly. And if you are not doing it very often, you forget how to. Its possible to tweak open loop phase shift even further if you settle for less closed loop bandwidth but you shouldn't, because you'll end up with an amp with maybe 35dB NFB applied at say between 500Hz and 5kHz, and each side of the that the efectively applied NFB will reduce because of the reduction of OLG with networks. With such reductions of OLG, the reduction of distortion products at above 5kHz becomes less, and sound goes hard, most probably. How does one go about tweaking the open loop phase shift? Use the networks detailed and shown in all my many amp schematics at my website. If you cannot understand the networks, build samples and measure them until you do know what to expect. Its all just basic applied and practical LCR theory. 30dB of NFB was applied around a large number of amps back in the 1960s to get typical THD 0.05% at a dB below clip at 1kHz, R load only. So at 3 watts typical was 0.02%. Companies liked to take part in wars of Watts, and battles of THD to get sales. These days many tube amps seem to have power quoted at 1% THD. In the 60s+70s 0.1% was more common. By the 60s, tubes were still mainstream, and many articles and reviews on amps mainly considered the technical aspects. A radio or sound system once was the most complex gear in anyone's house, and reading audiophiles had little to do in evenings except read audio mags while listening to their latest audio gear acquisitions. So readers all knew basic aspects about THD and its legacy of related IMD etc. TV started a lot of rot. Later, when tubes got mainly dumped, and THD went down below 0.01%, the technicals became unimportant, and looks and features and utter ****ing bull **** about sound became the norm. Readers went dumb, and houshold gear couldn't be understood any longer; it either worked or it didn't, and any co-relations between sound quality and where the transistors were made was all mainly boring BS. By mid 70s, most young folks were into hi-fi because it was a backround noise to accompany early family life and/or seduction of the liberated woman who was by then taking the Pill and who could be seduced 4 times week with the Beatles or Fleetwood Mac playing along and life was grand. The same ppl now rarely play a tune, and goodness me, rootin the missus with candle light and fine wine and fine music simply isn't on, and ears ain't what they used to be, the missus sure ain't, and the Picture comes first now, so most ppl have huge screen size for HT, and ****house sound quality, and its a much more distracting balm against the realization that the older they get the better they was. Many tube amps are made so badly now that they dare not mention the technical specs. And if you ever draw a graph of the distortion against output voltage you'll see that THD is very low while the amp is in class A, and then it increases more rapidly above the A to AB threshold, but which really only need to handle transients such as drum beats and cannon shots. Yes I have done that, and also compared a KT88 Class A with a KT88 AB1 at various levels. I also plotted distortion against frequency at various levels. Now that's an eyeopener! Yes, you get more THD at 10Hz and 40kHz than at 1kHz. Its a function of OLG and amount of applied NFB. Best not to worry that a typical 50W PP tube amp will double its 1kHz THD at say 30Hz and 20kHz. It does not matter. Patrick Turner. Iain |
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#21
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Iain Churches wrote: "Nick Gorham" wrote in message ... Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ Hello Nick. Lovely job:-) I have sent the pics to a couple of chaps with whom I share a workshop. The Tentlabs units are a nice and simple way of heating DHTs, I asked about these, because, as I mentioned to you before I want very much to build a good SET and have been collecting info and ideas for a while now. AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I don't think that's obsessive. My own view is that the amp should be silent from the listening position. It is not too difficult to build a PP of say 50W which is totally silent EAS (ear against speaker) but SET is a totally different challenge. Why is SET a special challnge for noise? I was thinking about AC heaters. I have heard only a few SET amps, but all of them, with one exception (Russian built) had audible hum from the listenking position. Hence my interest in Nick's amp, and his choice of Tentlab. My 60W amps with a parallel pair of 845 with very little global FB pass the EAS test easily. At a metre, there is no indication they are switched on except visually. Initially, this was not the case with an un-potted PT crammed onto the same chassis as the audio circuitry. Yes. I found the same thing. If you want the extra few dB in the SNR ratio, a separate PSU is a good solution. The power supplies are now separate from the audio amp chassis. the PT, OPT, and the two chokes for the choke input PS for dc heating of cathodes are all potted, and mechanically inaudible beyond 300mm. Here in the EU, it is very difficult (if not impossible) to find a DC connector approved for domestic use above 70V. Even the multi-pin NATO connectors which were used used for high voltage DC in broadcast are rated much lower for domestic applications. The use of octal plugs/sockets does not meet the safety standards, I am told by an assurance safety assessor, and no safety inspector would agree to such a thing being used these days for DC power. Using headphones across the output soon tells you about amp noise. Yes indeed. I have been working on a single-ended headphone amp. Just a few mW are needed to drive a splendid old pair of Koss Pro IVs I use, and also the Sennheiser HD280s which are my cans of choice for editing (they show up every tiny glitch) I know a guy with TL12 Leak amps which he's trying to use with Lowther horns. Hum is his enemy, and he hasn't a clue how to reduce it. Are you going to help him out? Iain |
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#22
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Then as you add NFB, you can draw a plot of the margin of stability if you really must, and by the time you have say 30dB applied, Iain wrote: Never managed to get that far 26dB is my best:-) I got 35dB max global NFB with the early version of 8585 which has about 12dB NFB in the output stage from the CFB connection while in class A where OP tube gain is maximal. The Radford STA 35 has 24dB of NFB and is completely stable. John Widgery, who was Radford's chief engineer told me that Arthur Radford was one of the few people who understood trannsformer design, and thought it important enough to make them properly. I usually check the response of the amp open loop, and then add a 10k pot for Rfb. I decrease the value until the amp starts to oscillate and then back off ten (or more) dB Its OK, but you are not changeing the OLG phase character to suit the wanted NFB, or the compo cap across the Rfb, or the gain step networks to reduce gain at extremes of F. There are actually about 5 things to be juggled, not just 1. Yes. I see. I am just looking at the output power, the input sensitivity and the THD. After about 20 amp projects, and trying to see just what has to be done to get stablity good and bandwidth wide with global NFB, you'll get the hang, while appreciating the old fashioned empircals. Each amp is a separate challenge in itself it seems to me. I am never entirely satisfied. Some people build tube amps without taking any test measurements, they just check the wiring and the DC conditions, and start top play music. They always seem happy:-) I have found the use of Sowter transformers make the task of building a stable amplifier easier than Hammond. Once I have got the Rfb sorted out, and replaced with a fixed R then I start to look at the stability into O/C and a cap. Once again, I use empirical methods, but the more you do it, the better you get at it:-) Exactly. And if you are not doing it very often, you forget how to. I make careful sketches and keep notes. How does one go about tweaking the open loop phase shift? Use the networks detailed and shown in all my many amp schematics at my website. I bought a dedicated phase shift meter (working it all out from elipses on the CRO was a tad too difficult) My 25Wamp is +5 degrees at 10Hz and -30degrees at 100Hz. If you cannot understand the networks, build samples and measure them until you do know what to expect. Its all just basic applied and practical LCR theory. But there are so many variables - so much going on at once:-) Regards Iain |
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#23
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: "Nick Gorham" wrote in message ... Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ Hello Nick. Lovely job:-) I have sent the pics to a couple of chaps with whom I share a workshop. The Tentlabs units are a nice and simple way of heating DHTs, I asked about these, because, as I mentioned to you before I want very much to build a good SET and have been collecting info and ideas for a while now. AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I don't think that's obsessive. My own view is that the amp should be silent from the listening position. It is not too difficult to build a PP of say 50W which is totally silent EAS (ear against speaker) but SET is a totally different challenge. Why is SET a special challnge for noise? I was thinking about AC heaters. I have heard only a few SET amps, but all of them, with one exception (Russian built) had audible hum from the listenking position. Hence my interest in Nick's amp, and his choice of Tentlab. See the info at http://www.tentlabs.com/Products/Tub...ent/index.html My 60W amps with a parallel pair of 845 with very little global FB pass the EAS test easily. At a metre, there is no indication they are switched on except visually. Initially, this was not the case with an un-potted PT crammed onto the same chassis as the audio circuitry. Yes. I found the same thing. If you want the extra few dB in the SNR ratio, a separate PSU is a good solution. The power supplies are now separate from the audio amp chassis. the PT, OPT, and the two chokes for the choke input PS for dc heating of cathodes are all potted, and mechanically inaudible beyond 300mm. Here in the EU, it is very difficult (if not impossible) to find a DC connector approved for domestic use above 70V. Even the multi-pin NATO connectors which were used used for high voltage DC in broadcast are rated much lower for domestic applications. I just use plain old octal plugs and sockets, OK for one offs. To each amp there 3 umbilical cables lightly twisted. Two are 10 amp rated 450Vac rated mobile crane wire, *nice* and flexible One is an orange twin mains cable, but only for low voltage dc for turn on and the protect circuit. If the octal plug going into the PSU is pulled out and grabbed with a hand the DC flow from the amp is prevented by diodes facing the appropriate way. Unless someone has a pet dobberman or pet lion prone to enjoying a bit of a chew on soft plastic things, then the cables won't be dangerous. The animals definately will stop chewing the cable at some point in time if the amps are turned on. I am using +680Vdc and -600Vdc approx, and careful layout of octal socket pins with some adjacent pins not used will prevent any arcing. The use of octal plugs/sockets does not meet the safety standards, I am told by an assurance safety assessor, and no safety inspector would agree to such a thing being used these days for DC power. I understand. I don't think my set up is unsafe. after all, HV is above 1,000V, no? Using headphones across the output soon tells you about amp noise. Yes indeed. I have been working on a single-ended headphone amp. Just a few mW are needed to drive a splendid old pair of Koss Pro IVs I use, and also the Sennheiser HD280s which are my cans of choice for editing (they show up every tiny glitch) I know a guy with TL12 Leak amps which he's trying to use with Lowther horns. Hum is his enemy, and he hasn't a clue how to reduce it. Are you going to help him out? Several long emails after the first, he might have got hum to 3dB less than it was. I can't get him to MEASURE things properly, and INVESTIGATE, and the LEARN, and to STUDY, and to ASK WHY, and all that basic stuff I've been doing for years. Maybe I get him over the line though. Old Leaks and Lowthers are not a good combo with regard to hum. He's in Italy, and I said find some old guy who knows about Geloso amps, and he should be able to work a Leak out. Most guys who might know anything in most Italian towns like Sienna have long since died. Patrick Turner. Iain |
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#24
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Patrick Turner" wrote in message ... Then as you add NFB, you can draw a plot of the margin of stability if you really must, and by the time you have say 30dB applied, Iain wrote: Never managed to get that far 26dB is my best:-) I got 35dB max global NFB with the early version of 8585 which has about 12dB NFB in the output stage from the CFB connection while in class A where OP tube gain is maximal. The Radford STA 35 has 24dB of NFB and is completely stable. John Widgery, who was Radford's chief engineer told me that Arthur Radford was one of the few people who understood trannsformer design, and thought it important enough to make them properly. Apart from Arthur, I am the other guy. I usually check the response of the amp open loop, and then add a 10k pot for Rfb. I decrease the value until the amp starts to oscillate and then back off ten (or more) dB Its OK, but you are not changeing the OLG phase character to suit the wanted NFB, or the compo cap across the Rfb, or the gain step networks to reduce gain at extremes of F. There are actually about 5 things to be juggled, not just 1. Yes. I see. I am just looking at the output power, the input sensitivity and the THD. After about 20 amp projects, and trying to see just what has to be done to get stablity good and bandwidth wide with global NFB, you'll get the hang, while appreciating the old fashioned empircals. Each amp is a separate challenge in itself it seems to me. I am never entirely satisfied. Some people build tube amps without taking any test measurements, they just check the wiring and the DC conditions, and start top play music. They always seem happy:-) I have found the use of Sowter transformers make the task of building a stable amplifier easier than Hammond. Once I have got the Rfb sorted out, and replaced with a fixed R then I start to look at the stability into O/C and a cap. Once again, I use empirical methods, but the more you do it, the better you get at it:-) Exactly. And if you are not doing it very often, you forget how to. I make careful sketches and keep notes. How does one go about tweaking the open loop phase shift? Use the networks detailed and shown in all my many amp schematics at my website. I bought a dedicated phase shift meter (working it all out from elipses on the CRO was a tad too difficult) My 25Wamp is +5 degrees at 10Hz and -30degrees at 100Hz. Numbers shumbers. Just do an XY on the CRO and with 0 degrees phase shift at say 1kHz, you see a slanting line. Phase shift either way shows up as an elipse at first, and then at 90 degrees it becomes a circle, and it SO EASY. You actually don't need to get exact numbers using my methods. There are no critical calculations required. Where needed, Zobel networks across the 1/2 primaries of the OPT are based on making the load to the output tubes resistive somewhere above 20kHz, so where RLa-a is 5k, you'd choose about 2k7 plus 0.022 as a Zobel. Why?, because the pole for the R&C is at 27kHz, easily calculated by a dumb school boy. The R damps the otherwise resonant behaviour of the OPT somewhere above 20kHz. But the CRO is your eye upon the wave, and the means by which a response is plotted, because the CRO makes a great volt meter. Again you do not need exact numbers, Seeing the amplitude drop by half its amplitude means -6dB, two lines down from 0dB in an exercize book, 1 line = -3dB, 2 = -6, 3 = -9, 4 = -12 and so on, and an amp response can be drawn, hard copy, in 8 minutes, 4 for HF, 4 for LF. Square wave testing also tells you a lot you need to know about critical damping and stability. For zobels across V1 RL, I use a radio tuning cap in series with a linear pot of 25k. DC is kept out with a 0.1uF cap. The effect of changing R&C values for the Zobel MUST be monitored with a CRO and square wave with 0.22uF load. "tune" the R&C for least ring at 1VO, using a 5 kHz square wave. If you cannot understand the networks, build samples and measure them until you do know what to expect. Its all just basic applied and practical LCR theory. But there are so many variables - so much going on at once:-) There is nothing that capable person with average intelligence cannot figure out. Engineers of the past like Arthur at Radford were pretty ordinary people. Amps ain't like sending a guy to the moon. And BTW, the waves are all going through the amp at the same time, just their phase relationships vary. Most ppl get confused about phase lead, or advance, and can't understand that it would appear the electricty arrived at its destination before starting out on the journey. They understand phase lag, oh yeah, they all know about a train or bus that was late. There is rarely any amp I cannot stabilize for unconditional stability. I have not met one yet where I cannot apply 15dB global NFB and still get 10Hz to 30kHz, -3dB into the rated load. Sometimes I have to use more than global 'series voltage' NFB, and I have to apply some global 'series current' NFB, as in the case of the Leak amp I worked on, see my page at http://www.turneraudio.com.au/leakampmods.html Patrick Turner. Regards Iain |
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#25
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Iain Churches wrote: The Radford STA 25 has 24dB of NFB and is completely stable. John Widgery, who was Radford's chief engineer told me that Arthur Radford was one of the few people who understood trannsformer design, and thought it important enough to make them properly. Apart from Arthur, I am the other guy. Actually there are two other guys. You and Brian Sowter (We won't mention Per Lundahl, as he doesn't read this NG) Iain |
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#26
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: The Radford STA 25 has 24dB of NFB and is completely stable. John Widgery, who was Radford's chief engineer told me that Arthur Radford was one of the few people who understood trannsformer design, and thought it important enough to make them properly. Apart from Arthur, I am the other guy. Actually there are two other guys. You and Brian Sowter (We won't mention Per Lundahl, as he doesn't read this NG) Well of course. Arthur Radford is maybe dead, and never seen here, nor is Brian Sowter. It would appear Brian wouldn't like to part with his expertise and detailed sectional drawings of bobbin winding details because he's the usual secretive guy who runs a business so busy he'd never have time for us. Per Lundahl is nowhere to be seen. A hundred other capable designers are nowhere to be seen. But that might be all the OPT designers in the world....... I don't have a clue really. Never fear, I am 'ere! Patrick Turner. Iain |
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#27
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: The Radford STA 25 has 24dB of NFB and is completely stable. John Widgery, who was Radford's chief engineer told me that Arthur Radford was one of the few people who understood trannsformer design, and thought it important enough to make them properly. Apart from Arthur, I am the other guy. Actually there are two other guys. You and Brian Sowter (We won't mention Per Lundahl, as he doesn't read this NG) Well of course. Arthur Radford is maybe dead, and never seen here, nor is Brian Sowter. Yes AR is probably now in the great transformer winding shop in the sky. He retired to due ill-health in the early 80's. Now *that* would have been a firm worth investing in to ensure its continuity, but it was Mr Radford's wish that the firm should close. I see there is a new company now with the name Radford Audio.Their website says they plan to continue the Radford tradition. They are probably trying to cash in on a legendary name, and have no product at the moment. It would appear Brian wouldn't like to part with his expertise and detailed sectional drawings of bobbin winding details because he's the usual secretive guy who runs a business so busy he'd never have time for us. Groups like this one are too much of a chimp fight for people like Brian Sowter, Morgan Jones, Per Lundahl, and a number of very capable people from the BBC, Swedish and German Broadcast They do contribute and discuss in closed groups to which the semi-literate and socially challenged (many of who inflict their presence on us here) have no access. Regards Iain |
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#28
Posted to rec.audio.tubes
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211 A2 amp
"Patrick Turner" wrote in message ... Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: "Nick Gorham" wrote in message ... Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ Hello Nick. Lovely job:-) I have sent the pics to a couple of chaps with whom I share a workshop. The Tentlabs units are a nice and simple way of heating DHTs, I asked about these, because, as I mentioned to you before I want very much to build a good SET and have been collecting info and ideas for a while now. AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I don't think that's obsessive. My own view is that the amp should be silent from the listening position. It is not too difficult to build a PP of say 50W which is totally silent EAS (ear against speaker) but SET is a totally different challenge. Why is SET a special challnge for noise? I was thinking about AC heaters. I have heard only a few SET amps, but all of them, with one exception (Russian built) had audible hum from the listenking position. Hence my interest in Nick's amp, and his choice of Tentlab. See the info at http://www.tentlabs.com/Products/Tub...ent/index.html My 60W amps with a parallel pair of 845 with very little global FB pass the EAS test easily. At a metre, there is no indication they are switched on except visually. I am very interested to build a good quality SET. I shall be grateful for advice from yourself, Nick, Andre (and of course anyone else who actually has hands-on experience) There will probably be lots of flames too, but who cares. I'm still going to build it:-) I will start a new thread whehn the time is ripe. The power supplies are now separate from the audio amp chassis. the PT, OPT, and the two chokes for the choke input PS for dc heating of cathodes are all potted, and mechanically inaudible beyond 300mm. Here in the EU, it is very difficult (if not impossible) to find a DC connector approved for domestic use above 70V. Even the multi-pin NATO connectors which were used used for high voltage DC in broadcast are rated much lower for domestic applications. I just use plain old octal plugs and sockets, OK for one offs. To each amp there 3 umbilical cables lightly twisted. Two are 10 amp rated 450Vac rated mobile crane wire, *nice* and flexible One is an orange twin mains cable, but only for low voltage dc for turn on and the protect circuit. If the octal plug going into the PSU is pulled out and grabbed with a hand the DC flow from the amp is prevented by diodes facing the appropriate way. The diode option is one thing that I looked at. I decided, after speaking with the insurance evaluator, to use a safety loop and a relay. Unless someone has a pet dobberman or pet lion prone to enjoying a bit of a chew on soft plastic things, then the cables won't be dangerous. The animals definately will stop chewing the cable at some point in time if the amps are turned on. But if the animal is a potential Cruft's champion..... I am using +680Vdc and -600Vdc approx, and careful layout of octal socket pins with some adjacent pins not used will prevent any arcing. The use of octal plugs/sockets does not meet the safety standards, I am told by an assurance safety assessor, and no safety inspector would agree to such a thing being used these days for DC power. I understand. I don't think my set up is unsafe. after all, HV is above 1,000V, no? We are talking about the LVD (Low Voltage directive here) which seems to go to 1500 V ! It's very difficult indeed to "interpret" the directives. I think the only sure way is to take an amp for inspection. In Scandinavia we have the FIN, SE and N standard. If the unit pases any of these, then CE is is assured. I am sure you have something similar in Oz. In addition a director of the company has to sign a declaration which is given to the owner with the manual, which states that the unit fully meets current safety requirements. The test is very expensive (several thousand Euros) The last time I asked about it, they required two identical units, both of which are tested to destruction (mains transformer current capacity, winding isolation etc etc) I pointed out that the Sowter transformers which I use already have a test certificate at CE rating - but, it seems that does not make any difference. The other problem I had was that I wanted a preliminary inspection (someone to cast a beady eye over the amp) and comment if there were any obvious breeches of the regulations that could be detected visually. They were not willing to do this. But I have found out quite a lot of info on the way - things that are considered to be crucial. They are, as far as tube amps are concerned, mainly to do with safety - earth bonding etc etc. One interesting thing is that many modern amps use crimped connectors on the mains input, AC switches, fuses etc right up to the primary of the PT. It is difficult to believe that a crimped connector is stronger or more reliable than a solder joint, but it seems that the regs call for a mechanical joint. A chap of my acquaitance who is involved with the design of GSM stations for Nokia told me that a "mechanical joint" is, in his opinion, not a crimped connector at all, but a wire passed through the eyelet on the switch tag, bent over and then soldered, so that it hgas mechanical strength and cannot become detatched if the joint is dry. I have also be told (by a my less reliable source) that the green/yellow earth wire on the mains connector must be five cms longer than the other two wires so that if the connector is pulled out accidentally, the earth will be the last connection to break. Hmm! I wonder!! Are you going to help him out? Several long emails after the first, he might have got hum to 3dB less than it was. I can't get him to MEASURE things properly, and INVESTIGATE, and the LEARN, and to STUDY, and to ASK WHY, and all that basic stuff I've been doing for years. Maybe I get him over the line though. He has to be willing to make some effort. manybe when he starts to get results he will become encouraged. DC heaters on the first stage are, I would have thought, the first requirement. Old Leaks and Lowthers are not a good combo with regard to hum. I can believe it:-) He's in Italy, and I said find some old guy who knows about Geloso amps, and he should be able to work a Leak out. The Leak schematics are easily obtainable. There is a guy in Oz (whose name escapes me) who runs a Leak site. Regards Iain |
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#29
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: The Radford STA 25 has 24dB of NFB and is completely stable. John Widgery, who was Radford's chief engineer told me that Arthur Radford was one of the few people who understood trannsformer design, and thought it important enough to make them properly. Apart from Arthur, I am the other guy. Actually there are two other guys. You and Brian Sowter (We won't mention Per Lundahl, as he doesn't read this NG) Well of course. Arthur Radford is maybe dead, and never seen here, nor is Brian Sowter. Yes AR is probably now in the great transformer winding shop in the sky. He retired to due ill-health in the early 80's. Now *that* would have been a firm worth investing in to ensure its continuity, but it was Mr Radford's wish that the firm should close. I see there is a new company now with the name Radford Audio.Their website says they plan to continue the Radford tradition. They are probably trying to cash in on a legendary name, and have no product at the moment. It would appear Brian wouldn't like to part with his expertise and detailed sectional drawings of bobbin winding details because he's the usual secretive guy who runs a business so busy he'd never have time for us. Groups like this one are too much of a chimp fight for people like Brian Sowter, Morgan Jones, Per Lundahl, and a number of very capable people from the BBC, Swedish and German Broadcast They do contribute and discuss in closed groups to which the semi-literate and socially challenged (many of who inflict their presence on us here) have no access. The tall poppies you mention couldn't stand the flak, and wouldn't like their names dragged into the sewers by the anti tube brigade. Unlike them I feel I have nothing to loose, no matter how submerged I am in ****e and other trashy arguments. Patrick Turner Regards Iain |
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#30
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: "Patrick Turner" wrote in message ... Iain Churches wrote: "Nick Gorham" wrote in message ... Hi Iain, I have added a couple of inside pictures to http://www.lurcher.org/nick/images/211/ Hello Nick. Lovely job:-) I have sent the pics to a couple of chaps with whom I share a workshop. The Tentlabs units are a nice and simple way of heating DHTs, I asked about these, because, as I mentioned to you before I want very much to build a good SET and have been collecting info and ideas for a while now. AC is cheaper, but I get a little obsessive about hearing hum, and I have never got hum low enough to not hear it. I don't think that's obsessive. My own view is that the amp should be silent from the listening position. It is not too difficult to build a PP of say 50W which is totally silent EAS (ear against speaker) but SET is a totally different challenge. Why is SET a special challnge for noise? I was thinking about AC heaters. I have heard only a few SET amps, but all of them, with one exception (Russian built) had audible hum from the listenking position. Hence my interest in Nick's amp, and his choice of Tentlab. See the info at http://www.tentlabs.com/Products/Tub...ent/index.html My 60W amps with a parallel pair of 845 with very little global FB pass the EAS test easily. At a metre, there is no indication they are switched on except visually. I am very interested to build a good quality SET. I shall be grateful for advice from yourself, Nick, Andre (and of course anyone else who actually has hands-on experience) There will probably be lots of flames too, but who cares. I'm still going to build it:-) I will start a new thread whehn the time is ripe. The simplest easiest way to SET is to use parallel multigrids connected as triodes. A six pack of 6L6GC will give you a sublime triode amp for 42 watts. Its a cheapest solution, and because the OPT load would be approx 900 ohms : 5 ohms, it is very easy to wind. The power supplies are now separate from the audio amp chassis. the PT, OPT, and the two chokes for the choke input PS for dc heating of cathodes are all potted, and mechanically inaudible beyond 300mm. Here in the EU, it is very difficult (if not impossible) to find a DC connector approved for domestic use above 70V. Even the multi-pin NATO connectors which were used used for high voltage DC in broadcast are rated much lower for domestic applications. I just use plain old octal plugs and sockets, OK for one offs. To each amp there 3 umbilical cables lightly twisted. Two are 10 amp rated 450Vac rated mobile crane wire, *nice* and flexible One is an orange twin mains cable, but only for low voltage dc for turn on and the protect circuit. If the octal plug going into the PSU is pulled out and grabbed with a hand the DC flow from the amp is prevented by diodes facing the appropriate way. The diode option is one thing that I looked at. I decided, after speaking with the insurance evaluator, to use a safety loop and a relay. The danger is if the umbilical cables are pulled out of the PSU while the power is on, and someone grabs the male pins feeding the power amp. The HT still at the power amp can shock someone. The diodes stop this, but a relay and discharge R can pull the B+ or B- down within 2 seconds anyway. Unless someone has a pet dobberman or pet lion prone to enjoying a bit of a chew on soft plastic things, then the cables won't be dangerous. The animals definately will stop chewing the cable at some point in time if the amps are turned on. But if the animal is a potential Cruft's champion..... Well, I sell so few amps that the chances of any of them killing a prize pet are remote. Cables to lamps and other appliances with 240Vac would pose more danger and be the more likely target of the animal who likes chewing on stuff. I am using +680Vdc and -600Vdc approx, and careful layout of octal socket pins with some adjacent pins not used will prevent any arcing. The use of octal plugs/sockets does not meet the safety standards, I am told by an assurance safety assessor, and no safety inspector would agree to such a thing being used these days for DC power. I understand. I don't think my set up is unsafe. after all, HV is above 1,000V, no? We are talking about the LVD (Low Voltage directive here) which seems to go to 1500 V ! It's very difficult indeed to "interpret" the directives. I think the only sure way is to take an amp for inspection. In Scandinavia we have the FIN, SE and N standard. If the unit pases any of these, then CE is is assured. I am sure you have something similar in Oz. In addition a director of the company has to sign a declaration which is given to the owner with the manual, which states that the unit fully meets current safety requirements. The test is very expensive (several thousand Euros) The last time I asked about it, they required two identical units, both of which are tested to destruction (mains transformer current capacity, winding isolation etc etc) I pointed out that the Sowter transformers which I use already have a test certificate at CE rating - but, it seems that does not make any difference. Here in Oz its legal to sell a wide range of electrical items including audio amps which don't need to be submitted for safety approval by approveved NATA labs. All electricals do have to satisfy Oz Standards re safety issues. So if one used all approved designs of mains trannies and didn't wind one's own, then its easier to comply. But no matter how well you comply, or how well you prove that your device was safe, if your device kills or maims someone, the judgement will be made against you. But In Oz there has not been a successful case made against any maker of amplifiers. Its easy to make something safe enough to make it extremely unlikely it would kill or maim. C-tick compliance about stray noise being radiated or injected into mains is a separtae different issue to safety and is the Oz version of CE compliance and is based on voluntary compliance. No need to spend any money if you prove to the Communications Authority that you test the gear and it complies. But at some future time, probably the laws will change and make it very difficult to sell tube amps at all. The other problem I had was that I wanted a preliminary inspection (someone to cast a beady eye over the amp) and comment if there were any obvious breeches of the regulations that could be detected visually. They were not willing to do this. But I have found out quite a lot of info on the way - things that are considered to be crucial. They are, as far as tube amps are concerned, mainly to do with safety - earth bonding etc etc. One interesting thing is that many modern amps use crimped connectors on the mains input, AC switches, fuses etc right up to the primary of the PT. It is difficult to believe that a crimped connector is stronger or more reliable than a solder joint, but it seems that the regs call for a mechanical joint. A chap of my acquaitance who is involved with the design of GSM stations for Nokia told me that a "mechanical joint" is, in his opinion, not a crimped connector at all, but a wire passed through the eyelet on the switch tag, bent over and then soldered, so that it hgas mechanical strength and cannot become detatched if the joint is dry. The regs are manily totally ignored by the flood of asian crap purchased online, and never subjected to serious inspections at entry. Regs here were designed to stop the asian crap entering, and to ensure asian crap was made to be safe, and not cause interference. Piles and piles of the utter rubbish floating in from asia have serious safety and noise issues. Soldering in HK Hi-Fi branded amps is attrocious. I have also be told (by a my less reliable source) that the green/yellow earth wire on the mains connector must be five cms longer than the other two wires so that if the connector is pulled out accidentally, the earth will be the last connection to break. Hmm! I wonder!! Most people here making stuff make this a feature. I use an IEC chassis shielded filtered plug which has a metal case which is bolted to the chassis, and this case is also connected to the green/yellow wire. But I earth it anyway with the lead going to a lug with nut and bolt. If the mains is tugged, the mains lead pulls harmlessly out of the amp or PSU. Are you going to help him out? Several long emails after the first, he might have got hum to 3dB less than it was. I can't get him to MEASURE things properly, and INVESTIGATE, and the LEARN, and to STUDY, and to ASK WHY, and all that basic stuff I've been doing for years. Maybe I get him over the line though. He has to be willing to make some effort. manybe when he starts to get results he will become encouraged. DC heaters on the first stage are, I would have thought, the first requirement. Old Leaks and Lowthers are not a good combo with regard to hum. I can believe it:-) He found he has earth loop bothers because if he runs each amp of two to different power points, one hums when the other is used. A common power point might help. He converted to triode operation of the EF36 input tube and had a big hum reduction. He's in Italy, and I said find some old guy who knows about Geloso amps, and he should be able to work a Leak out. The Leak schematics are easily obtainable. There is a guy in Oz (whose name escapes me) who runs a Leak site. I have the TL12 original schematic at my site, and he has the original amps. So he is at the best site for TL12 mods, ie, my own. But he still cannot even measure the simplest thing.... Patrick Turner. Regards Iain |
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#31
Posted to rec.audio.tubes
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211 A2 amp
Iain Churches wrote:
Yes AR is probably now in the great transformer winding shop in the sky. He retired to due ill-health in the early 80's. Now *that* would have been a firm worth investing in to ensure its continuity, but it was Mr Radford's wish that the firm should close. I see there is a new company now with the name Radford Audio.Their website says they plan to continue the Radford tradition. They are probably trying to cash in on a legendary name, and have no product at the moment. Iain, just FYI, I don't know what their plans are, but the group that has the Radford name now, are the same people who produce the World Designs kits. http://wduk.worldomain.net/ I have spoken with Peter who runs the group several times now, and his area of design is loudspeakers (he was tech director at Mission), he would be the first to admit that he is not specialist when it comes to valve amps, so normally uses Andy Grove for design work. I suspect he will do the same with the Radford name. -- Nick |
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