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#1
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Tube replacements for Icon Audio MB 845
I recently purchased (swapped actually) a pair of Icon Audio MB 845 MkII monoblocks which I'm very, very happy with. I've never run an amp with 845 valves before and wonder if I'm going to have trouble replacing them when I need to? Emails to Icon have so far gone unanswered so I'm wondering if there are any other sources for these valves or have I gotten myself a future problem?
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#2
Posted to rec.audio.tubes
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Tube replacements for Icon Audio MB 845
On Apr 13, 11:21*pm, Fred Dag
wrote: I recently purchased (swapped actually) a pair of Icon Audio MB 845 MkII monoblocks which I'm very, very happy with. I've never run an amp with 845 valves before and wonder if I'm going to have trouble replacing them when I need to? Emails to Icon have so far gone unanswered so I'm wondering if there are any other sources for these valves or have I gotten myself a future problem? -- Fred Dag The only 845 tubes you should consider using are Shuguang 845, type B. I have custom built SE amps using pairs of KR Audio 845 which are 4 times the price of the best Chinese 845 from Shuguang. See my web page..... http://www.turneraudio.com.au/monobloc845se55.html I don't think the KR sound any better than the Shuguang. And KR use oxide coated cathodes like a 300B and probably don't have such a long life as the thoriated tungsten cathodes because the oxide coated cathodes are prone to positive ion bombardment once Ea goes above about 1,000V, although KR themselves said to me 1,200V is OK. Tungsten cathodes are best. For lowest hum, DC should ONLY ever be used for heating with a balanced circuit for cathode as seen at my schematic for 845, where there are two 33VA DC power supplies for the 845 cathodes. I also repair and re-engineer some very nice looking GARBAGE which has 845 tubes or 300B etc and built by rogues in the UK or by chinese but sold as made in the UK with badges maybe being the only thing made in the UK. I am presently repairing a pair of Ming Da 100W PP class AB amps which I suspect were formerly designed by a desperate old Chinese dude with dementia. His efforts ensured that smoke production would soon follow a brief period of music & noise. I even had to replace ALL 2W resistors used throughout the amps where Vdc across the R exceeded 100Vdc because resistors went open with no sign of heat stress. In amps like these there are many resistors with over 300Vdc across them and it invites failure. Ming Da has 845 working in class AB1 to make 85Watts with Ea = 1,200Vdc, fixed bias of -190Vdc, and Ia at idle = 42mA, for Pda = 50 Watts at idle. Originally the Pda was a dangerous 100W. Just idiocy. Methinks that where you try to extract 115W in class AB1 or AB2, you might be trying to flog the crap out of the tubes, or else the Ea might be 1,500V with a very high primary load on the OPT, but this is unlikely, and probably the RLa-a is way too low because most designers are unwilling to make a wide bandwidth OPT for 20k : 4, 8 & 16 ohms. The Icon Audio website is most UN-INFORMATIVE, plenty of sales lies, but no technical details, such as a full schematic. I find that PP 845 can be excellent, but the same can be said for any other OP tube. The sound is determined mainly by the design integrity, choice of input and driver tubes, how they are set up, choice of loading, amount of global NFB and how well critical damping is done. Usually most manufacturers build their amps so that if you connect 8 ohms to a n output socket labelled "8 ohms", this is where the absolute maximum possible power is produced. If you have 8 ohm speakers, ignore the 8 ohm outlet if you have an outlet labelled "4 ohms" because the use of 8 ohms will double the anode load experienced by the output tubes, double damoing factor by halving output impedance and halving THD and IMD. The maximum PO will drop to maybe 85 Watts, but I bet you only ever need 10 Watts like everyone else unless you are trying to vainly impress your pretentious mates that you have something bigger than they do. Try clipping a peak and hold DMM across your OP terminals to find out how little power you need when you are using the amp during times when you are not turning it up just to temporarily impress somebody. Patrick Turner. |
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#3
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Quote:
"Unlike transistors, designed for general industrial use, possessing inadequacies for audio amplification covered over with an electronic sticking plaster called feedback, the big 845's possess no intrinsic weaknesses as far as audio is concerned. Their drawbacks are the obvious ones of size, weight and heat. An emerging radio industry soon demanded smaller size and power consumption so valves like this were quickly superseded, but sound quality didn't benefit from miniaturization. That's why this amplifier also uses early, large bulb 6SN7 and 6SL7 triodes. They sound better - smoother, more relaxed and fluid than later, smaller, 1950's B7G and B9A based valves. And if you spotted that the two 6SL7's have charred black glass envelopes that make them look like burnt out seconds, they are in fact new, top quality 'Treasure Series' Shaguangs from China. The black staining comes from improved gettering, a process that eliminates gas residues after evacuation of the bulb. Yep, This amplifier may look retro but every valve in it is a new variant of an old design, using best quality modern materials and construction techniques. Designer David Shaw told me he tried the latest metal anode Shaguang 845's (845C) that have higher power handling but preferred the graphite anode originals, albeit in improved 845B form as fitted to our amplifier. This doesn't surprise me in the least. A sonic feature of the 845 is the characteristically dark, damped sound of its graphite anode, a quality many listeners remark upon.. . . . . Higher power output from a single pair of 845 valves demands a more serious power supply so the mains transformer has grown substantially too. The H.T. is a frightening 1250 volts and uses diode rectification plus choke smoothing. Driving and 845 is no easy task; often a 300B valve is valve is used but this is a ridiculously expensive solution. Designer David Shaw has instead used two 6SN7 double triodes, each strapped as a single, one per phase, each choke loaded for maximum voltage swing. The three chokes are now housed in their own screening cans on to of the chassis and you can see them as three smaller units sitting alongside the giant mains and output transformers. The front end paraphrase splitter is a 6SL7 and it provides gain too. Running as recommended in lower sensitivity mode, input sensitivity is a normal 1V for full output. . . . . ." That'll mean more to you Patrick than it does to me. I'm just an electronics ignoramus lucky enough to be wallowing in the best sound I've ever heard coming out of any thermionic or solid state device - and I've tried a few over the decades. The preamp I'm using is from Leben. Last edited by Fred Dag : April 14th 11 at 11:45 PM Reason: Correction to valve numbers and spelling |
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#4
Posted to rec.audio.tubes
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Tube replacements for Icon Audio MB 845
On Apr 14, 7:07*pm, Fred Dag wrote:
Patrick Turner;929716 Wrote: On Apr 13, 11:21*pm, Fred Dag wrote:- I recently purchased (swapped actually) a pair of Icon Audio MB 845 MkII monoblocks which I'm very, very happy with. I've never run an amp with 845 valves before and wonder if I'm going to have trouble replacing them when I need to? Emails to Icon have so far gone unanswered so I'm wondering if there are any other sources for these valves or have I gotten myself a future problem? -- Fred Dag- The only 845 tubes you should consider using are Shuguang 845, type B. I have custom built SE amps using pairs of KR Audio 845 which are 4 times the price of the best Chinese 845 from Shuguang. See my web page..... * *http://www.turneraudio.com.au/monobloc845se55.html - - - - - -but I bet you only ever need 10 Watts like everyone else unless you are trying to vainly impress your pretentious mates that you have something bigger than they do. Try clipping a peak and hold DMM across your OP terminals to find out how little power you need when you are using the amp during times when you are not turning it up just to temporarily impress somebody. Patrick Turner. As always Patrick, your expertise and generosity in explaining things is in evidence. *Thanks - *it's a shame though I'm an electronic ignoramus and therefore can't understand most of what you're relating. *I just happened to fall in love with the music the Icon Audio MB 845's make through my speakers, Usher BE 10's with the beryllium mid & treble drivers, and swapped them on impulse. The previous owner emailed me a review of them from Hi-Fi World Magazine, most of which you'd probably get more out of than I do. Here's a few extracts :- "Unlike transistors, designed for general industrial use, possessing inadequacies for audio amplification covered over with an electronic sticking plaster called feedback, the big 845's possess no intrinsic weaknesses as far as audio is concerned. Their drawbacks are the obvious ones of size, weight and heat. Back when the 845 was initially released for sale by RCA (?) it was another high fallootin cutting edge device made by carefully trained people and would have probably many week's of pay so nobody used them except ppl owning commercial radio stations. But of course the cost of production in China in real terms is minsicule, and to buy an 845 the cost is maybe 1/10 of a week's pay for a develped nation person earning $60,000 a year. I found I could get 27W from a single 845 with Pda = 72Watts. To achieve the same power with smaller tubes you'd need three 300B or 6550 strapped as a triode and in parallel. Much of the audiophile world judges the 300B SE amp on the basis of what just ONE 300B gives, and never upon what 3 might give is paralleled. The audiophile prejudices are rather short sighted. I would suggest that were anyone to compare the performance of a single 845 to 3 x 300B ( or 3 x 6550 ) if designed and manufactured by the same person to get the best performance then I doubt many would pick any difference in sound. Using 3 x 300B would cost more than using one 845. An emerging radio industry soon demanded smaller size and power consumption so valves like this were quickly superseded, but sound quality didn't benefit from miniaturization. That's why this amplifier also uses early, large bulb 6SN7 and 6SL7 triodes. They sound better - smoother, more relaxed and fluid than later, smaller, 1950's B7G and B9A based valves. I like 6SN7. They made many thousands here in Oz. Their design varied with early types using cylindrical anodes and later types using rectangular anodes about 25mm long, 3.5mm x 10mm sections. In about the 1950s when post WW2 demand surged for TVs and the rest, the 6CG7 was invented. It was just a mini 9 pin tube with the SAME box type of anode, grid and cathode as used in 6SN7, just moved together a little, and the tube Pda rating was reduced marginally. I don't believe the sound quality suffered. In Germany, the mini 9 pin 6CG7 was made with smaller box section anodes, smaller grids and cathodes to give a triode which have near equal technical performance to 6SN7. A number of audiophiles here tell me the Siemans 6CG7 made in 1960s was THE BEST signal triode ever made. I have a number of NOS 6CG7 made in Oz and which I have trialed against Siemans and found virtually no sonic differences - BOTH are excellent. So I cannot generalise by saying all small package tubes are worse sounding than the preceding types which were octal or whatever else was used. I find headphone amps made using 6BQ5 or EL86 in triode and with decent OPT to be utterly blame free. I also find these same pentodes strapped as triodes offer fabulous dynamics as driver tubes for larger output tubes. And if you spotted that the two 6SL7's have charred black glass envelopes that make them look like burnt out seconds, they are in fact new, top quality 'Treasure Series' Shaguangs from China. The black staining comes from improved gettering, a process that eliminates gas residues after evacuation of the bulb. The "black glass" tubes were very common. I've seen many ancient blacked 6L6, 6V6, ECC32, 6SN7 et all. The Chinese didn't invent the process. And where you may see black glass tubes from China, perhaps its done to pretify the tube rather than for any scientific reason. Yep, This amplifier may look retro but every valve in it is a new variant of an old design, using best quality modern materials and construction techniques. Yes, but anyone building any tube amp now benefits from modern materials and construction techniques because that's about all that are avaialable, such as computer controlled metaworking gear. But without a schematic publically available I cannot endorse anything some other maker ever might do. HOW tubes are employed in a circuit is probably more important than tube choice or brand of tube. Designer David Shaw told me he tried the latest metal anode Shaguang 845's (845C) that have higher power handling but preferred the graphite anode originals, albeit in improved 845B form as fitted to our amplifier. This doesn't surprise me in the least. A sonic feature of the 845 is the characteristically dark, damped sound of its graphite anode, a quality many listeners remark upon.... I am not exactly sure how one scientifically defines "dark, damped sound" and so I can only smile when I hear such vague terms used, bearing in mind that one might get 10 different versions from 10 different audiophiles about a given audio experience. 10 different wine tasters might assess 10 different bottles of wine in 10 different orders of preference. And both the audiophiles and wine tasters can easily be fooled by a double blind test. OK. But I don't set out to make a fool of anyone. I have tried replacing a bunch of Sovtek 300B in a VAC 7070 amp which was spitting tubes out and making noise and smoke. It sounded good with only 3 of the 4 tubes in each channel still working with another 2 quite faulty. But the owner put in Sophia carbon plate 300B and had me revise the whole terrible circuit of VAC, and yes, people who know the amp must revise their ideas about what 300B can or cannot do. The remarkable thing is that triode amps can have very serious faults and still sound fine at 2 watts which is all most audiophile ever use. The excellent sound of a quad of PP 300B is easily reproduced with 845 in SE, - OR - PP, or by 6550, KT88 etc used in a variety of ways. . . . . Higher power output from a single pair of 845 valves demands a more serious power supply so the mains transformer has grown substantially too. The H.T. is a frightening 1250 volts and uses diode rectification plus choke smoothing. 1,250Vdc is a dangerous anode voltage, but many amateur radio operators had RF amps with 2,500V and rather high voltage anode signal swings using a variety of tubes. With 1,250Vdc, there is often 3 electrolytic caps in series, each with 450Vdc rating. There is always more riskof something failing sooner rather than later as complexity and anode supply voltages are raised. Driving and 845 is no easy task; Nope, its dead easy. Just follow my circuit at my 845 pages where I use a choke + resistance to supply 3 paralleled EL84 in triode. often a 300B valve is valve is used but this is a ridiculously expensive solution. The Ming Da PP amps with 2 x 845 in PP have 300B drivers with resistance loads and the Chinese designer had set them up attrociously so that they ran out of puff all too soon, and contributed far too much of the total amount of THD from the amps. Any, I made all this right in the Ming Da by using a split rail so Ea was nice and high, Ia is now twice the tiny amount used by dopey Chinese designer, and all is well. Uising a CT choke plus anode resistors would even be better, but I found the sound "went to excellence" with pure resistance loading. But 300B have lousy low gain of only 4, so the Ming Da need a 6SN7 LTP ahead of 300B balanced driver amp, and an SE input stage also using 6SN7. I like to use one stage less, just input, driver, and output. Designer David Shaw has instead used two 6SN7 double triodes, each strapped *as a single, one per phase, each choke loaded for maximum voltage swing. Lord knows why ppl do this trick when a balanced driver amp sounds just as good if not better. The three chokes are now housed in their own screening cans on to of the chassis and you can see them as three smaller units sitting alongside the giant mains and output transformers. Manufacturers always like to claim superiority for their techniques, but I can't see any in using a pair of SE stages to drive each output tube phase of a PP pair. Each SE driver would produce more IMD products than a decent balanced PP driver stage. IMD is always poisenous to music. The front end paraphrase splitter is a 6SL7 and it provides gain too. I don't like para phase because the output of one triode is divided down to drive the other triode of the paraphase pair. The stage gain is effectively doubled with positive FB so the THD of such a stage is also increased. I use 6SL7 to drive EL34 in triode which drives 13E1 with 33% CFB in the OP stage of my SE32 amps. The max drive voltage required at 13E1 grids with the local NFB is over 100Vrms, about the same as 845. The EL34 gain = 8, so max signal from SE 6SL7 ( paralleled ) is 12.5Vrms, and 6SL7 has gain = about 35, so roughly 0.35Vrms input is needed for clipping without NFB. With a small amount of global NFB, input sensitivity is between 1 and 2Vrms. If I'd used EL84 as the driver, then driver gain = 17, and then input could have been 6CG7, and it would only have to produce about 6Vrms. Total open loop gain, applied NFB and sensitivity would be the same. But methinks the 6CG7 input tube would have to be better than 6SL7. I like the 6SL7 - if you can ever find a nice quiet sample. Running as recommended in lower sensitivity mode, input sensitivity is a normal 1V for full output. *. . . . ." I have not sighted a schematic, so I should not cast any opinion about how sensitivties claimed are achieved. Perhaps with "lower" sensitivity he means a higher input voltage is needed for say 100W, and maybe more NFB is used than where the sensitivty is "higher" when a low input voltage is needed for 100W. All very confusing to all, and an indication David Shaw has some serious communication short comings. How come infomation at his website is not backed up with schematics with all working voltages shown? The website presentation is sloppy, a con job, like so many websites. I like total transparency. Unfortunately, I have had to rewire many amps promoted at websites with confusing info; it indicates the product is produced by an entrepreneur who knows **** all about anything technical, and that behind the scenes there is often some low paid donkey worker who knows barely enough to get it working without smoke for perhaps the warranty period. The amps are made primarily to look pretty and sell fast. But they don't work very well when closely analysed. A classic example is the Quad 40. Designed by Andy Grove. A good guy. But the Quad 40 is basically exactly the same circuit as the Quad-II, designed in around 1950 by Peter Walker. Walker's old design is being recycled and rather murdered a bit by Chinese implememtation. So what did dear old Andy have to do with it? I guess the marketting smart arses ( who never contribute to anything sounding better ) needed a name to link circuit design to a famous someone alive, not dead, like Dear Peter. Sales would be better if Andy was in the loop, rather than not in the loop. No doubt Andy got paid. But I've repaired Qaud 40 and I cannot see much improvement over Quad-II. Build quality seems muddled compared to anything Walker would have let out the factory gate. That'll mean more to you Patrick than it does to me. I'm just a simpleton wallowing in the best sound I've ever heard coming out of any thermionic or solid state device and I've tried a few over the decades. The preamp I'm using is from Leben. The reason why tubed amps are still selected by many despite higher cost, finite tube life, occasional tube failures, heat, weight, etc, is that they seem to do a better job of amplifying than is done by many solid state jobbies. Some tube amps manage this even when designed by a moron. Good tube amps promote themselves. All I have to do is keep tubes all working happily with selected loads in class A and the tubes keep everyone happy with the sound. For me this means building a much better amp than Peter Walker or Andy, and better than a shirt&trouser load of many other wannabes. If Peter was a young man around now, I'm sure the 2011 version of Quad-II would be far far better than the old design which was indeed limited by the absense of Si diodes, high value electrolytics, decent EI laminations, etc. I am presently trying to get the three ghosts of Peter W, Harold Leak, Mr Radford to form a design consulting firm for tube amps "as they really would have liked to make without accountants poking their nose in". So far, attempts have been lacklustre. When Peter and Harold appear at 2AM in my lounge they start arguing with each other over biasing and whether pentodes or triode drivers should be used. Not even the damned experts can ever agree about anything. Radford is depressed, he reckons new tube amps ain't what they used to be in the good old days.....I tried to calm him by saying its OK and we all know that potatoes grown in 1950 were better than grown last year, but there have been other happy advances. But they still bicker. Patrick Turner. -- Fred Dag- Hide quoted text - - Show quoted text - |
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#5
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Tube replacements for Icon Audio MB 845
Quote:
Again Patrick I understood little of the technical side of your response although I'm sure others will get a lot out of it. All I know is that I've spent a lifetime trying various amps both SS and thermionic and the Icon Audio MB 845 gets me more excited than anything I've previously run, including some silly money Class A solid state monsters from Mr Pass. Mind you, I've had to hand over everything below 45Hz to a pair of Velodyne DD14 sub-woofers as I found the Icon Audio didn't have that last degree of speed down below and running my main speakers full range always presents me with a choice between the best imaging and worst bass performance or best bass performance and worst imaging etc due to the size and shape of the room itself. So, with the two DD15,s I can get the best of both worlds and somehow don't notice any gap between them and the Usher BE 10's. Last edited by Fred Dag : April 17th 11 at 03:59 AM Reason: Forum software insisting on using post first line as a heading - Mad! |
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#6
Posted to rec.audio.tubes
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Tube replacements for Icon Audio MB 845
On 04/16/11 19:57, Fred Dag so wittily quipped:
I've spent a lifetime trying various amps both SS and thermionic and the Icon Audio MB 845 gets me more excited than anything I've previously run, including some silly money Class A solid state monsters from Mr Pass. Mind you, I've had to hand over everything below 45Hz to a pair of Velodyne DD14 sub-woofers as I found the Icon Audio didn't have that last degree of speed down below and running my main speakers full range always presents me with a choice between the best imaging and worst bass performance or best bass performance and worst imaging etc due to the size and shape of the room itself. So, with the two DD15,s I can get the best of both worlds and somehow don't notice any gap between them and the Usher BE 10's. ultimately it boils down (like application of music theory) to "does it sound good?" And good choice using two subwoofers instead of 'one for both channels'. I dislike those single-subwoofer systems. To me they just "sound wrong". |
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