NOSValves Posted February 22, 2013 Share Posted February 22, 2013 Are those wild looking tubes even available? I did a search and can not find anything other then related to this manley amp. Seems like they would be available some where. If they are that hard to find I'd be stocking up!ML has a lot of them in stock but I bought four more with the amp. Eve Anna has used her for almost ten years and the output tubes are still fine. BTW what would be the life expectancy for the other four tubes in the amp? Yea that is a old electronics manufacturing trick. Make an amp out of really hard to find tubes or transistors then buy up all remaining stock to control the tube/transistor replacment business for your amplifiers. If I ended up really liking the amp I'd be getting lots of spare tubes and would not believe everything I hear about longevity... How much were the 4 spares? Quote Link to comment Share on other sites More sharing options...
bracurrie Posted February 23, 2013 Author Share Posted February 23, 2013 How much were the 4 spares? $25 each, guaranteed for life. Tube life that is.[6] Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 28, 2013 Share Posted February 28, 2013 Not sure if this thread prompted the email I recieved yesterday but a VRD owner asked if I had ever thought of rewiring for this tube since it was available so cheap....evidently Manley did not buy up the entire remaining stock. He sent me this link I hope it doesn't make you cry. http://www.tubes-store.com/product_info.php?products_id=183 Quote Link to comment Share on other sites More sharing options...
philipbarrett Posted February 28, 2013 Share Posted February 28, 2013 I wouldn't cry. Manley throw away a lot of tubes and only sell those that have passed their verification tests. Quote Link to comment Share on other sites More sharing options...
bracurrie Posted February 28, 2013 Author Share Posted February 28, 2013 Is the GU50 the same as the GY50 that is in the Manley Labs Euro 100 amp? I hope it doesn't make you cry.No cry. Me happy. But thanks Craig. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 28, 2013 Share Posted February 28, 2013 I wouldn't cry. Manley throw away a lot of tubes and only sell those that have passed their verification tests. Can I possibly sell you a bridge or maybe lake front desert property [] Quote Link to comment Share on other sites More sharing options...
Deang Posted February 28, 2013 Share Posted February 28, 2013 Any tube that doesn't light or sounds like a baby rattle flunks our rigorous testing procedures. Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 2, 2013 Author Share Posted March 2, 2013 Today, in the amp I changed out the 12AT for 12AU and attached in an ohmite adjustable resistor to make the tweeter horn less efficent. I moved the adjuster until the idle noise was below room noise threshold from my listening position. Wow, it worked. Now I know how much added resistence I need to make the tweeter horns less efficent to mask the system noise. Of course until I can do a proper gain analysis of my equipment chain I will keep the ohmites just in case I can recover some efficiency. Quote Link to comment Share on other sites More sharing options...
Marvel Posted March 2, 2013 Share Posted March 2, 2013 Not sure if this thread prompted the email I recieved yesterday but a VRD owner asked if I had ever thought of rewiring for this tube since it was available so cheap....evidently Manley did not buy up the entire remaining stock. He sent me this link I hope it doesn't make you cry. http://www.tubes-store.com/product_info.php?products_id=183 It's a Russian company... but seem to have a good reputation. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 2, 2013 Share Posted March 2, 2013 Today, in the amp I changed out the 12AT for 12AU and attached in an ohmite adjustable resistor to make the tweeter horn less efficent. I moved the adjuster until the idle noise was below room noise threshold from my listening position. Wow, it worked. Now I know how much added resistence I need to make the tweeter horns less efficent to mask the system noise. Of course until I can do a proper gain analysis of my equipment chain I will keep the ohmites just in case I can recover some efficiency. You changed the AT7 for the AU7 with no other changes to the amplifier? If so that ought to make some nice added distortion. Also a single resistor is not the proper way to knock down the tweeter. You need to build an L-pad or much better buy tweeter attentuators from Al Klappenburger. Here is an online Lpad calculator http://www.sengpielaudio.com/calculator-Lpad.htm Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 3, 2013 Author Share Posted March 3, 2013 The resistor was placed in parallel. How is that different from an Lpad? Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 5, 2013 Author Share Posted March 5, 2013 You changed the AT7 for the AU7 with no other changes to the amplifier? The tube change was recommended by Manley Labs as was an added resistor to increase negative feedback and reduce gain. There is no audible change in distortion, but a great deal quieter at idle.You need to build an L-pad or much better buy tweeter attentuators from Al Klappenburger.Yes I agree, but with a 16 ohm tweeter I thought I would try the quick, dirty and cheap first as I had more than enough damping factor to play with. Ok, now I am convinced so I am going to either build my own with parts from a passive network or buy Al's transformer tweeter attenuator.Thanks Craig for your thoughtful post. Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 6, 2013 Author Share Posted March 6, 2013 As pretty much a final post on this subject. I was disappointed by the noise from the amp. I have now installed an attenuator that uses a transformer much like Al K's and it works much better than the plain resistor setup I tried first to tame noise by making the tweeter horn less efficient. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 7, 2013 Share Posted March 7, 2013 You changed the AT7 for the AU7 with no other changes to the amplifier? The tube change was recommended by Manley Labs as was an added resistor to increase negative feedback and reduce gain. There is no audible change in distortion, but a great deal quieter at idle. If all you did was add a resistor to increase negative feedback then the change from AT7 to AU7 added some distortion, sorry to say there is no way around it. While the AU and AT are pin compatible series of tubes they take different plate load, cathode resistor and voltages to operate in there most linear curve. So if that is the case you indeed added some amount of distortion along with some smearing increased negative feedback brings to the table..Like everything in life no free lunches... Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 7, 2013 Author Share Posted March 7, 2013 Craig - Thanks for the observations. I am learning about things through the generous time you and others are sharing by reading and replying to my posts. Like everything in life no free lunches... It was mentioned to me that the small amount of negative feedback increase would tend to offset the increase in distortion from the tube change, but even then it was said that the impact would be very small. Evendently David Manley when he designed these did alot of his work by the seat of his pants and the (I may get this wrong) his choice of plate resistors would be to the low side for the tube he chose to use.(I really don't know this material very well.) So I could go from 80k to 60k but that the change would be very very small to audio quality. My question would be given that I am using the amp only from 200 to 20,000 with very efficent drivers would I be better off returning to the original design spec for the negative feedback and the AT7 given that I have discovered transformer tweeter atttenuators to tame the noise? Quote Link to comment Share on other sites More sharing options...
LarryC Posted March 8, 2013 Share Posted March 8, 2013 Of course until I can do a proper gain analysis of my equipment chain I will keep the ohmites just in case I can recover some efficiency. Well! The ARC 6b is supposed to have a gain switch, apparently on the rear panel. The following is from a couple of posts on Vinylengine.com:The Audio Research has an adjustable gain switch on the rear, with a choice of High or Low output." To see if I remember right I looked at a schematic here: http://www.arcdb.ws/SP6/ARC_SP6_schematic1.gif. The rear panel switch ony impacts the gain of the line stages and should not impact the phono equalization. Phono stage gain is spec'ed at 34 dB while overall gain is 60 dB, -10 dB with the gain switch set to "low". It is fairly quiet as 12AX7 based preamps go ... The odd thing is that the SP6 sounds so different with the gain setting to high. It should not. The SP6b's line stage gain is 26 db, which is rather high. My former CAT preamp had 26db linestage gain, which was too much -- it increased preamp noise through the speakers, and made the volume control sit right at the bottom of its range, where it didn't belong. A 10 db decrease to 16 dB could be very helpful in reducing your noise, because I am pretty sure the noise you're hearing is from the preamp. Can you find a switch, is it on "high" or "low," and what effect does it have on noise and sonic quality? Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 9, 2013 Author Share Posted March 9, 2013 because I am pretty sure the noise you're hearing is from the preamp.What you have to remember is that in my case the preamp is driving the miniDSP not the amps. The noise is coming from the miniDSP most probably. When I disconnect the preamp from the miniDSP there is no change in noise. When I turn the gain down on the miniDSP there is no change in noise. Also there is no difference in using the phono stage in either switch position or the other inputs on noise.The amp itself is also part of the noise problem. When I hooked up my Adcom gf255 there was a dramatic decline in noise, but also no life in the sound. Quote Link to comment Share on other sites More sharing options...
LarryC Posted March 9, 2013 Share Posted March 9, 2013 OK. Does the Manley have more gain or higher sensitivity than the Adcom?. I can't find Adcom 255 on Google Quote Link to comment Share on other sites More sharing options...
bracurrie Posted March 9, 2013 Author Share Posted March 9, 2013 OK. Does the Manley have more gain or higher sensitivity than the Adcom?. I can't find Adcom 255 on Google I made a mistake the Adcom is a GFA-535 and it has an input sensitivity of 970 mV and (S/N) ratio is 110 decibels. The Manley Labs Euro 100 has an Input sensitivity: 800mV and a S/N ratio: 80dB. Thanks again Larry for chiming in. Quote Link to comment Share on other sites More sharing options...
LarryC Posted March 9, 2013 Share Posted March 9, 2013 OK, Adcom's 970 mV in for 60 W out vs. ML's 750/800 mV in for 100 W out. Doesn't seem to be a huge difference. Thanks. Quote Link to comment Share on other sites More sharing options...
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