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In Reply to: Re: 6as7 life continued... posted by bryan on February 16, 2005 at 06:08:34:
Bryan, Since you have 8 X 6AS7 sections per phase (two per tube), it seems unlikely to me that one or two bad sections would seriously affect your listening pleasure. More than once I have noticed that my own MA240s sound just a tad "off" but still excellent and then found out that the cause was due to blown fuses on one or up to three out of six of my output tubes. In other words, it's surprising how subtle the differences are when one or a few output tubes are not doing anything at all, let alone just losing transconductance. All of this is to say that I would take a hard look at your input and driver stages. Check the coupling caps too.
Follow Ups:
Thanks for the advice, Lew. I'm going to mail off my 6as7s to a friend and he'll have a listen to them and we'll see if he thinks they sound bad. I have experienced sections go on me and heard what that sounds like, but this is different. Could be what I'm hearing has nothing to do with the power tubes. If thats the case, I don't know what I'm going to do. I can't troubleshoot myself, and I don't want to ship my amps from Canada to the US.
> I'm going to mail off my 6as7s to a friend and he'll have a listen to them and we'll see if he thinks they sound bad.As several others have mentioned, you would need a set of desperately bagged-out tubes to notice any real shift in character. You might notice a loss of dynamics & overall power, but to get a change in tonality, mushy distortion, etc.. things would have to be well beyond just worn-out.
I tend to agree; there is likely something else going on here, if the amps are sounding truly 'bad'.
If you knew enough to measure the current through your tube sections ("50 to 80mA"), then perhaps we can talk you through checking the input stage. Obviously there is some danger involved due to proximity to high voltages, but if you keep one hand in your pocket at all times while taking measurements and do nothing else silly, then you would be OK, if you have a VOM. First, is the "problem" identical in both amplifiers? Have you checked out your preamp and/or other front end gear to be certain that nothing is wrong with them?
Hi Guys !!After using Atma-sphere OTL's for a number of years I think that I have become so spoiled to listening to a super transparent, smooth musical signal that when it changes for some reason we noticed it right away. I have chased my tail trying to find solutions to all sorts of noise and anomalys and when the day was done it was mostly due to bad line voltage. The noisy AC line can cause us to notice all sorts of things with these OTL's. I have noticed that when the AC line voltage is relatively clean that I hear a very smooth and dynamic presentation( ie. very late at night or early am like one or two in the morning). However, when the AC is dirty the signal becomes hashy and sluggish and sometimes hard and brittle. So, what's the solution ???? Well---pick your poison and buy or try the myriad of different types of power line conditioners. I have not bought one yet because the majority of the time my amps sound damn good. When I first bought my MP3 I had a annoying buzzing sound from my tweeter. I bought a couple of Quite line AC filters (the cheap little black boxes) that you plug in to your AC outlets. The buzz went away completely----so I came to the conclusion that allot of the problems we have is because of this dirty AC. I am going to buy a good isolation transformer and see if it it helps. Anyway---that's my 2 cents worth.
I also forgot to mention that all of the stuff( computers,halogen lights,digital components, etc)that we have plugged in at our houses really pollute our AC lines. I have noticed that even with dedicated lines the pollution still spills over into these lines. Maybe, it's the RF or EMI. I really don't know because I am not an EE. This really is apparent with Halogen and flourensent lights.
RF and EMI are issues, but one of the major problems caused by what we call 'electronic loads' (computers, audio equipment, flourescent lights) is distortion of the AC waveform.. When the AC waveform is a perfect sine, all is well, but when it becomes distorted, you not only have additional line noise to squash, but the *power factor* of the line falls off.It's very possible to read "120 volts" at the outlet, but if the power factor is off due to waveform distortion, the actual power that the line can deliver to the load can be considerably lower than expected.
Interesting to see that you feel dedicated lines are not the answer at least to AC noise generated in your own home. I have found with four dedicated 20-amp lines powering my audio system that my system sounds just about the same at any time of day, i.e., darn good. Have you checked to see whether the ground side of your dedicated AC line(s) is/are isolated from "house ground". My dedicated lines are grounded to separate copper poles imbedded in the ground (literally) outside my house, well away from house ground. Perhaps this makes a difference.The various methods for cleaning AC are all meritorious in their own ways, but one must be careful with large tube power amps, which consume power in big gulps, that the device, whatever it is, does not delimit the current available for the amplifier. Brian's problem seems more severe than that which we normally attribute to AC grundge. For one thing, he hasn't said that it's time-of-day dependent. If you get an isolation transformer, make sure it's industrial size. Overkill always makes us audiophools feel good.
Hi Lew,I do believe that dedicated AC lines and grounds are better than undedicated---However, they are not an end all answer to noisy AC. I do have dedicated grounds and I would probaly have more noise than I do now if I had the opposite.I would presume that every house is different in the amount of noise and grundge but I do know that late at night (10 pm to 2am) that my equipment sure sounds allot better--so the only conclusion is that the AC must be influencing my equipment.
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