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I don't think so at all....

Posted by andy evans (A) on September 16, 2014 at 18:55:14

In Reply to: Its getting worse !! posted by drlowmu on September 16, 2014 at 08:58:52:

...Nice of you to share. What does the B+ supply schematic, with DCRs, look like ??>>

I leave that to whoever builds it. I'm not political about power supplies.

...Your FIRST and foremost problem is you ten inch speaker is NOT sensitive enough. This is the root of all your tube amplifier problems IMHO.If you had 100 dB sensitive speakers, you could design VERY good tube amps and make easier aural determinations easier.>>

It's a Mark Audio Alpair 10 which is more like 5". But it sounds good and covers the full range. If I got into lighter paper cones I might run into more breakup problems. I don't need a more sensitive speaker since the amp is plenty loud for my room fed with a 2v DAC. However, if I found a full range unit that sounded better than the Alpair, then sure I'd be interested in theory. Who wouldn't. There are some boutique speakers about at silly money but I don't feel any burning desire to upgrade. In an ideal world I'd have ribbons going down as low as possible, like B&G with a bass speaker crossing over as low as possible. I used to have Apogee Caliper Sigs which were streets ahead of anything else but they were too big for my room, especially when you brought them out from the walls. I have an apartment in central London and they don't come cheap, so space is expensive and at a premium. I have to have small footprint speakers close to walls, no way around that.

... I previously critiqued your amp as having too high a dissipation across the Finals tubes. You have "hot-rodded" and upped it even more, in the wrong direction. You are at 250.5 VDC plate to cathode, at a new and higher current, 36 mA. That is 9.01 Watts plate dissipation, on a 7.5 Watt rated plate. Why Why ?>>

Because it isn't a 7.5 watt rated tube. Add the screen and it's 9 watt. A few of us have done tests on the 4P1L (see Bartola Valves for example) and you will need to know that it sounds best around 25-30mA or even more. It's been used at 40mA. It likes current. And anyway I don't believe in the infallibility of the golden rule. But sure - try it at different wattages and see what sounds good to you.

...after 200 hours the higher dissipation advantages are lost, and after 2,000 hours the tubes are "toast" - need to be tossed. That is not good tube design>>

No - this isn't true at all. I leave my amp on 24/7. I replace the output tubes maybe every 6 months. They sound exactly the same after 200 hours and pretty much the same after 6 months. That's 30,000 hours. They're tough little things. And I have nearly 200 of them so what do I care! You're using expensive output tubes - I'm not.

... Recall how a listener to your system complained about the sound of violins, that is one place where a stressed thermally tube will sound bad. Your latest incarnation has upped the current even more.>>

That was something else which I fixed in subsequent iterations. But there's a germ of truth in this - using two of the same tubes in following stages can exaggerate harmonics. I don't find it a problem, furthermore many people are now starting to use 4P1L preamps and are loving the treble. It's better than the 26 for instance.

... I am not trying to criticise you, just giving you my thoughts from a few years of audio experience.>>

But bear in mind I've been building 4P1L amps and preamps for 3 years and gone through several iterations of them. So I'm 3 years ahead of you on this one. I think you'll like the tube, but you'd seriously love it in filament bias. It's the way to go.

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