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Old 31st March 2008, 02:23 PM   #11
kmaier is offline kmaier  United States
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Yes, I tend to agree that there are still 45s around, how many are all that great is a matter of opinion and personal subjectivity. As for running the filament, I prefer AC, not DC... and I think a DC filament will run them down quicker. For me, this means I reject a good percentage of the ones I have based on extensive testing and matching of pairs.

When I fit tubes for an amplifier I match in complete sets, not just the 45s, but the input/drivers and rectifiers as well. To get the best possible sound from a zero-feedback design, you need to spec groups of tubes for the amplifier(s). I match in complete sets for gain, noise, distortion and voltage before any listening is attempted. Testing for mechanical noise is also crucial.... can't tell you how many tubes I've found to be so sensitive to mechanical vibration (including the music itself) to make them useless in an amplifier.

While I fully realize 2 watts is only 2 watts, the requirement for ultra high sensitivity speakers (104dB) and a lower limit of 200Hz is also a matter of opinion (as you pointed out). For the 45 designs I've completed... I consider 50Hz the lower useful limit but ensure proper operation down another octave. I also like to see a flat response to at least 40KHz with 50KHz being the preferred 1db down point.

Also, the more sensitive your speakers are, the more critical the output noise of the amplifier becomes. This defines the useful dynamic range of the system in addition to having hum and noise as intermod distortion with all low level detail. A signal to noise ratio of 80dB (referenced to 1-watt) is a bare minimum... and with high sensitivity speakers, it's really not enough.

So far, I'm pretty happy using my 45 amps to drive the Feastrex D5nf. Yes, there is a definite upper SPL limit, but depending on the room, personal levels, etc. it can be more than adequate, but you're not going to get the last 2 octaves in full glory regardless... limits are still, well... limits.

Regards, KM
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Old 31st March 2008, 03:46 PM   #12
limono is offline limono  United States
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Thank You
Such a nice post , I don't have resources nor dedication to go to that extent of matching tubes and checking technical performance .I do use separate filament transformer with electrostatic shield and AC heating also PT and choke are somewhat separated from chassis and tube sockets (ordinary) use rubber grommets. The hum although noticeable when close to the driver is not an issue .I'd rather worry of those HF noises . At present I use Lowther DX4 in 204 Azura horn and even if I will probably tear the setup apart in the near future to address some inherent mid-bass , top end weaknesses it sounds really sweet.
Regards, L
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Old 23rd April 2008, 12:59 PM   #13
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Default Aarghs from the abyss: WE 211E ecstasy & agony

The owner of the amplifier and tubes shown above is now working part-time for Feastrex. All the people connected with Feastrex are big fans of tube amplifiers and at any given time there always seems to be at least one interesting amplifier project going on, albeit at the personal enjoyment level rather than as part of their business per se. I have a backlog of "Feastrex-related, tube-related" items that I'll try to add to this thread as time permits.

Some of these items will also be peripherally related to Feastrex speakers, such as what I'm going to write today -- that in some instances simply changing a certain type of tube from one brand to another could change the way the speakers are driven, to the degree that one feels a loudspeaker enclosure design modification might be in order to accommodate it. (I have not confirmed this myself and am in no position to defend that last statement -- I'm simply passing on what another person has written about his experience.)

Anyway, the experience has proven rather mind-blowing, because nobody who has heard this tube would have expected it to make such a huge difference. The tube is the original Western Electric 211E.

The "ecstasy" is in the sound that these tubes produce -- beyond compare to any other 211 type tube that these people have encountered. The "agony" is their high price and the difficulty of maintaining a reliable supply of them today.

Click the image to open in full size.
Click the image to open in full size.

One of the monobloc amplifiers to which the above tubes have been added (the tube shown is of a different make):
Click the image to open in full size.
Click the image to open in full size.

Here are some comments from the amplifier's owner:

"Until we hooked up this amplifier, we thought the enclosure that we had designed for the prototype Feastrex field coil driver housed in it was just about perfect. We have found that when the driver and enclosure are properly matched to each other, problems arising from enclosure resonation seem to simply disappear. It's as if all the energy inside is coming out the port effortlessly and there is no residual energy to excite the enclosure itself. But when we hooked up this amplifier, the previously well-behaved enclosure started to act up. There was clearly a lot more energy to be dealt with here, and it really drove home to me the fact that in some cases at least it is not enough to think of the driver and enclosure as 'the loudspeaker system'; rather, for best results the driver, enclosure, and amplifier need to be all considered together. That means the choice of amplifier could have implications for the enclosure design. In some cases, to get truly optimum results, one might be forced to do several cut-and-try variations on a speaker where the differences are measured in millimeters. This experience has left a deep impression on me, because we have tried this combination of driver and enclosure with a wide range of amplifiers, and gotten basically similar (excellent) results with all of them, until this one came along. This amplifier seems to clearly have the potential to sound better that all the others, but it may very well mean modifying the enclosure in order to be able to take advantage of it.

"The other thing that comes to mind is that a good fullrange driver loudspeaker can be like an 'audio stethoscope' that really reveals everything in your system. A powerful tool for music reproduction is also a powerful tool for revealing every quirk and change in your system. Living with such a loudspeaker may not always be easy, but that's part of the price of admission to a world of better music reproduction.

"Anyway, this WE 211E is really amazing, and the WE 331A that came along with it perhaps even more so. These great old tubes from half or three-quarters of a century ago -- if we can put a man on the moon, why can't we produce modern tubes that are able to equal these?"

http://museum.ehost-services112.com/211e.html
http://museum.ehost-services112.com/we331a.html

-- Chris
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Old 23rd April 2008, 02:35 PM   #14
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Absolutely breathtaking. Only two words come to mind: "liquid sound" as in a crystal clear musical stream.

What are the input and driver tubes?

TIA,

-- josé k.
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