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The Headcase Stax thread


thrice

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I hope the board isn't fried somehow. :(

Could very well be but Stax in their infinite wisdom had to make it black... :mad: There are still quite a few parts that haven't been replaced and I haven't gone to the next step of swapping parts between channels as I don't want to mess with the good one. Who needs stereo anyways... :P Still the amp works with a -180v offset in one channel.

When did the absence of tube burn-in become some sort of orthodoxy?

New tubes drift like crazy so they need some time to settle and they will change. It's not the drastic transformation needed to make an RSA amp any good but it's there and varies from tube to tube.

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The best I found were Japanese tubes with a short "box" style plate. They are easily recognizable, as the plates only seem to fill half of the bottle. Some of these were rebranded by Raytheon, but not manufactured by them. I think the actual manufacturer was Toshiba, but it's possible that Toshiba also rebranded them from someone else.

US-made Raytheons have a full-size plate, and are sonically uninspired, IMO.

88x Tube 6FQ7 6CG7 RAYTHEON JAPAN NIB $5.8 Each Tube - eBay (item 5873841025 end time Jun-26-06 09:22:33 PDT)

Were they those ones? Suprising the page is still there.

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Huh?

Way back when on the other forum I posted impressions of a bunch of 12AT7 types for the MicroZOTL. I was moving as fast as I could to get a bunch of impressions up, but did wait on each tube set until I felt the sound had "stabilized" and I couldn't hear differences in brief listening sessions separated by at least an hour. None of the tubes had settled at five hours. Some started settling at 8-12 hours, and some took a day or two. It would not shock me if subtle changes occurred over longer periods, but that was not what I was listening for. I'm only citing periods where changes in sound were obvious and unmistakable.

When did the absence of tube burn-in become some sort of orthodoxy?

Orthodoxy? This is just my experience. Also notice that I say most tubes. I should have said "with the tubes I've tried".

My experience is also that any tube that didn't settle down (i.e. stop cracking or hissing) within the 5 hours, never did. Of course, I only tried for another 5 hours or so before either returning the tube or throwing it out. Once a tube has settled down, I never noticed it getting any better. I only noticed it subtly getting worse over time as it wore out. Even that I could only tell by swapping back to back with new tubes. That is until the tube got really close to failure. Then it was pretty obvious. It's amazing how one's brain adapts to slow changes.

New tubes drift like crazy so they need some time to settle and they will change. It's not the drastic transformation needed to make an RSA amp any good but it's there and varies from tube to tube.

I agree. This is also what I mean by "settle". This is probably real burn in and it doesn't take long to occur.

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Could very well be but Stax in their infinite wisdom had to make it black... :mad: There are still quite a few parts that haven't been replaced and I haven't gone to the next step of swapping parts between channels as I don't want to mess with the good one. Who needs stereo anyways... :P Still the amp works with a -180v offset in one channel.

I am obviously not an expert in fixing amps, but could board issues be detected using impedance tests with the amp turned off?

i would love to see that DBT'ed, though it would be an expensive test, i'm sure, as multiple identical amps would be required.

You can send the same signal to both channels, and test the channels against each other using custom adapters. You'd be listening to mono though.

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I just wanted to share my personal experience of the tubes, based on rather much listening with varying types of music, and not on a meet or something like that. Very shortly, that EH tubes are quite good and Raytheon lack in some aspects, in my experience and my system. In the beginning I was more positive to Raytheon, but still think it is very good.

I only have experience with EH 6SN7 tubes, so it may not apply to EH 6CG7 tubes. I also found them to be competent, but the least favorite 6SN7 or 7N7 I've heard. They lack the details and finesse of the NOS tubes I've heard. On the plus side, their price is right.

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My experience is also that any tube that didn't settle down (i.e. stop cracking or hissing) within the 5 hours, never did. Of course, I only tried for another 5 hours or so before either returning the tube or throwing it out. Once a tube has settled down, I never noticed it getting any better. I only noticed it subtly getting worse over time as it wore out. Even that I could only tell by swapping back to back with new tubes. That is until the tube got really close to failure. Then it was pretty obvious. It's amazing how one's brain adapts to slow changes.

Cracking and hissing are not normal sounds from good tubes. If you're lucky, it can be due to gas buildup that can dissipate when the tube is heated. Or, it could be some excess material deposited in the gap that simply burns off. Or, you could have a tube pin that is not making a good connection to the amp (clean your tube pins!). More often, it is a symptom of a tube with issues. The cracking sound is usually arcing between the grid and the plate, and you don't want it. At best it is annoying, at worst it can indicate that a full short is about to happen. If it doesn't disappear completely, in a fairly short time, and you know the tube is making a good connection at the pins, the tube is probably junk.

The adaption to slow changes is why I didn't allow myself to adapt. Short sessions well-spaced don't cause adaptation in the same way that continuous listening does. Try a short listening session with brand new tubes. Listen again at about ten hours, but only for a short time. Then try again at 100 hours (no cheating). You can't adapt if you're not listening. Results might surprise you.

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I am obviously not an expert in fixing amps, but could board issues be detected using impedance tests with the amp turned off?

That's what I've been doing and have found nothing besides some very bad soldering. I will fix it eventually but since it has been completely surplus to my needs I have just let it sit there. I'm going to use it in my computer rig for awhile to see if that will make me get off my ass and order a full set of new components for it.

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I only have experience with EH 6SN7 tubes, so it may not apply to EH 6CG7 tubes. I also found them to be competent, but the least favorite 6SN7 or 7N7 I've heard. They lack the details and finesse of the NOS tubes I've heard. On the plus side, their price is right.

We may agree to some extent. I don't know how similar these two EH tubes are but there could be similarities. The 6CG7 lacks finesse and it is not silky smooth or something like that but it has a neutral tone and good extension. I like it much more on the SR-404 than on the HE60 where it sounds too harsh. The SR-007 could be better to use as a reference but I haven't got it yet.

I have no definite idea of how long time it takes for tubes to burn-in and in some cases I have had other equipment that burned-in also and it is hard or impossible to isolate the effects. Maybe I have confounded and overestimated it but I have heard differences after 50 hours. There is a psychological aspect too but this also applies to other aspects of evaluating audio gear.

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That's what I've been doing and have found nothing besides some very bad soldering. I will fix it eventually but since it has been completely surplus to my needs I have just let it sit there. I'm going to use it in my computer rig for awhile to see if that will make me get off my ass and order a full set of new components for it.

I see. Once again, good luck with the repairs. I hope it gets fixed eventually. :)

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My new ESP/950 from Koss have around 100 hours on them, and so far I think they definitely sound a bit better than my old set I sent in (when they didn't have the squeal). There is now semblance of a soundstage, and they sound great at rock and jazz. They are competitive with the HE60, especially given the price the Sennheiser's fetch.

Come on KG, we need a portable estat amp, I want to take these to work :D

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I received my KGSS DX yesterday and I noticed it is making a weird "charging" sound that is somehow amplified when I move my head fast from left to right. It does that as soon as it is plugged on the wall, without any source connected. I opened it up this morning and noticed that there is a capicitor with one end floating around in the air, not touching anything. Any opinions?

IMG_1147.jpg

IMG_1148.jpg

P.S. Sorry for the crappy pics, I suck at photography.

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