Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: adamct on August 10, 2013, 06:43:56 PM
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OK, someone help me out. In January I bought one of those 6SN7 --> 12AU7 adapters on eBay. I got the one that appeared to be high-quality, with a nice ceramic socket and gold-plated pin holes. I think several others here have the same adapter. I made sure I got the 6.3V version. When it arrived, I tried it out with a couple of 6SN7s, but they all seemed noisy, although they were quiet in other amps. I chalked it up to some sort of bad "synergy" between the tubes and the Crack (w/ Speedball). I put the adapter to the side for a few months, until I got a couple more 6SN7s. Again, I pulled the adapter out and tried them with the Crack. Still noisy. Then I decided it must be the adapter. I contacted the seller, and although I was outside the complaint period, they gracefully sent me a new one at no charge (fast shipping from China, too, which is unusual). Tonight I try out the new adapter and...same problem.
Here is the exact situation: the noise is stronger in the left channel than the right. Much stronger. At low volume levels, the noise changes with the volume pot, but quickly hits maximum noise levels and stays constant after that. The tube plays music just fine - no cracking or popping or anything, just noise when I hit pause. My Crack is literally DEAD SILENT when I use it with my other input tubes, without an adapter. The noise doesn't change when I jiggle the RCA inputs. There shouldn't be any interference from other devices, as there aren't any nearby, and (again) the amp is quiet with other tubes. And the noise is the same no matter which 6SN7 tubes I use.
Anyone else have a similar experience? If so, how did you solve it? I know some people like 6SN7s with the Crack, but I can't imagine anyone would find this level of noise acceptable, so what I have must not be normal. Suggestions? What could be causing these problems?
Best regards,
Adam
P.S. I have heard from at least two other people who have had a similar problem, and were also unable to solve it. Is the 6SN7 just not suitable for the Crack? Is the adapter design somehow defective? Is anyone using 6SN7s via adapter without any noise?
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The 6SN7 works well in the Crack, I have used them plenty of times. Ultimately, it may be easiest to rewire the Crack to use the 6CG7/7AU7, or perhaps to try a simple 6.3V DC wall wart to power the heaters on the Crack to see if the AC that heats the tube is radiating to other parts of the tube in the adapter.
-PB
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Thanks, Paul. I might wind up trying an adapter from another vendor... :(
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Hi Adam,
I assume you ordered this adapter, right? http://www.ebay.com/itm/1x-6SN7-to-12AU7-Vacuum-tube-adapter-socket-converter-/300943315564?pt=Vintage_Electronics_R2&hash=item46119e926c
Try this one : http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=320659633166&ssPageName=STRK:MEWAX:IT#ht_1080wt_793
It looks cheaper and not as 'well-made' as the one you ordered, but it works well :)
Best regards,
Kratos.
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Dadgummit, Kratos, where were you 30 minutes ago?!? :P. I just bought one of these (http://www.ebay.com/itm/151094591086?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649). :-[ And you are right about the two that I currently have. I'll try the new one, and if that still doesn't work, I'll go for yours. Fourth time is the charm, right?
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Adam - I assume you may have already seen my posts in the other 6sn7 adapter thread? I first bought the adapter Kratos linked - which had exactly the same issue you describe in your OP (bad noise in one channel that increases with the pot). Then I bought the lowtherclub version you just ordered. It is the lesser of the two evils but still has a bit of noise in both channels.
Personally I'm throwing in the towel and will stick to buying more 12au7s and 12BH7s in the future - which all run dead quiet in my crack. Hope your second roll of the dice on an adapter goes better than mine did.
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Thanks, Mike. I'm inclined to agree with you...
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Dadgummit, Kratos, where were you 30 minutes ago?!? :P. I just bought one of these (http://www.ebay.com/itm/151094591086?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649). :-[ And you are right about the two that I currently have. I'll try the new one, and if that still doesn't work, I'll go for yours. Fourth time is the charm, right?
Haha, yeah, you're right. I have not tried any tube adapter that you ordered, but I hope that you won't need to go for the fourth tube adapter to enjoy the fantastic sound of the 6SN7s on the Crack :)
Best regards,
Kratos.
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The best part of all this is that I have no idea why I'm doing it, other than boredom. I love my Crack with 12AU7s / 12BH7s, tube rolling is not fun for me, and I don't really want to get into the morass of 6SN7s...
LOL --- we'll see. Maybe I'll be singing a different tube if I finally get an adapter that works...
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The best part of all this is that I have no idea why I'm doing it, other than boredom. I love my Crack with 12AU7s / 12BH7s, tube rolling is not fun for me, and I don't really want to get into the morass of 6SN7s...
LOL --- we'll see. Maybe I'll be singing a different tube if I finally get an adapter that works...
Tube rolling is one of the most fun and additive things in my audio passion, I enjoyed this as much as 'rolling' headphones or DACs :p
Good luck with your coming tube adapter!
Kratos.
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Maybe I'll be singing a different tube if I finally get an adapter that works...
That was not intentional, but it is one of the funniest Freudian slips I've seen...
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It may not be a problem with the adapter per say, but the fact that it adds extra wire, connections, stray capacitance and just more stuff to pick up noise...John
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If that's the case, then I wouldn't expect anyone to be able to run 6SN7s via adapter without picking up plenty of noise. I've heard people say they were using adapters and had zero noise. Frankly, "zero" can me something very different depending on who you talk to, but the noise I've experieed with two adapters so far wouldn't fit into anyone's definition of zero noise...
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The 6SN7 works well in the Crack, I have used them plenty of times. Ultimately, it may be easiest to rewire the Crack to use the 6CG7/7AU7, or perhaps to try a simple 6.3V DC wall wart to power the heaters on the Crack to see if the AC that heats the tube is radiating to other parts of the tube in the adapter.
-PB
So, my Lowther Club adapter arrived yesterday. It is a considerable improvement over my other two adapters. I was able to listen to one of my 6SN7s that I have been eager to hear in my Crack and actually here the 6SN7 / music, instead of just hearing static / noise. What I heard was very promising. Maybe even enough to make me eat crow and admit that tube rolling makes more of a difference than it has with the other XX tubes I've tried. But ultimately, there is still noise at an unacceptable level. During moderate to loud music passages, it isn't noticeable, but on quiet passage it intrudes. I have gotten used to my Crack being dead quiet and can't go back. So I either need to buy yet another adapter and knock on wood, or try your suggestion, PB.
What would I have to do to make this work? Will any 6.3V DC power supply work? Does it have to be exactly 6.3V or will 6V or 6.5V also work? Does it have to be linear? Regulated? Current rating? Where do I attach the leads, and what wires do I need to cut / desolder?
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Also, what did you mean by wire the Crack to use 6CG7/7AU7?
Thanks in advance,
Adam
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Hi Adam,
What tube adapter are you using? My tube adapter finally arrived today, and I'm using it with no problem. There is not ANY noise or hum, and the Crack is even quieter than when I was using the 12AU7's and E80CC's. The sound is significantly improved, more air, bigger soundstage, better dynamic and very nice sparkling treble. The 6SN7's change the sound more noticeable than any tube types I have tried before ( i.e, 12AU7, 12BH7, E80CC )
Some of the pics of my tube adapter. And sorry for the image quality, my iPod's camera just sucks :D
(https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-ash4/1003214_654603561218129_1949076875_n.jpg)
(https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-frc3/1186237_654603594551459_1364203996_n.jpg)
(https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-ash4/1005673_654603601218125_2013672518_n.jpg)
Very best,
Kratos.
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Yeah, I ordered that adapter last night. It will be adapter #4 for me... :(
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Yeah, I ordered that adapter last night. It will be adapter #4 for me... :(
Nice!
Good luck with your purchase :)
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Obviously all adapters are not made equally (tip of the hat to George Orwell).
Paully got some for his Eros and the first pair were perfect. With Altec Valencias then Model 19s he would know if there was noise.
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Ok, now it's my turn to have some problems with the tube adapter. I don't know where to post this, so Adam, forgive me if this post bothers you.
I got a Chinese adapter of which I took photos and posted above the page. As you all know, the Crack has plenty of power, so you'll have no problem to reach a preferable level before it's too loud at approximately 9 o'clock position ( the minimum volume is at 7 ), and me too. Today, I inserted my 6SN7 Raytheon VT-231 into the Crack using the Chinese adapter. The initial impression was amazing, dynamic and fantastic sound, no hum at all. But when I shut down my DAC and turned the volume pot to about 10.30 to 11 o'clock position ( which is far beyond my reference volume level ), the hum started to appear. It varies on the volume level, the louder the volume is, the louder the hum. But when the volume pot reached about 3 o'clock, it's dead silent again, no hum. So as long as I turned my volume of my PC ( DAC ) to max and turn the Crack's volume pot to about 9 o'clock, it will be fine. But this hum bothers me a little bit.
I tried my E80CC back to my Crack and it's back to silent again. So I assume this was due to the fact that the Crack is not designed for using 6SN7? Because of higher gain or heater current of the 6SN7's?
Thanks a lot!
Kratos.
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The noise could also be the tube itself. Have you tried another one? I had some NOS russian 6SN7 that were noisy. I was looking for all sorts of technical issues until I replaced them with Sylvanias from the mid 50's, which solved the problem for me. Just a thought as I dont have a crack, but another preamp using 6SN7s.
Best of luck
Michael
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Ok, now it's my turn to have some problems with the tube adapter. I don't know where to post this, so Adam, forgive me if this post bothers you.
I got a Chinese adapter of which I took photos and posted above the page. As you all know, the Crack has plenty of power, so you'll have no problem to reach a preferable level before it's too loud at approximately 9 o'clock position ( the minimum volume is at 7 ), and me too. Today, I inserted my 6SN7 Raytheon VT-231 into the Crack using the Chinese adapter. The initial impression was amazing, dynamic and fantastic sound, no hum at all. But when I shut down my DAC and turned the volume pot to about 10.30 to 11 o'clock position ( which is far beyond my reference volume level ), the hum started to appear. It varies on the volume level, the louder the volume is, the louder the hum. But when the volume pot reached about 3 o'clock, it's dead silent again, no hum. So as long as I turned my volume of my PC ( DAC ) to max and turn the Crack's volume pot to about 9 o'clock, it will be fine. But this hum bothers me a little bit.
I tried my E80CC back to my Crack and it's back to silent again. So I assume this was due to the fact that the Crack is not designed for using 6SN7? Because of higher gain or heater current of the 6SN7's?
Thanks a lot!
Kratos.
Hi Kratos
I have the same behaviour exactly with my adapter. When using 6SN7 tubes I set the Crack volume to maximum and control the volume through my preamp.
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The noise could also be the tube itself. Have you tried another one? I had some NOS russian 6SN7 that were noisy. I was looking for all sorts of technical issues until I replaced them with Sylvanias from the mid 50's, which solved the problem for me. Just a thought as I dont have a crack, but another preamp using 6SN7s.
Best of luck
Michael
I've tried 5-6 different 6SN7s.
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The noise could also be the tube itself. Have you tried another one? I had some NOS russian 6SN7 that were noisy. I was looking for all sorts of technical issues until I replaced them with Sylvanias from the mid 50's, which solved the problem for me. Just a thought as I dont have a crack, but another preamp using 6SN7s.
Best of luck
Michael
Hi Michael,
I have tried several 6SN7 tubes, and the noise is still there, perhaps it's slightly different depending on tubes, but just very slightly. All the noise is very noticeable and unacceptable. As soon as I turned the volume pot to about 11 o'clock, it started to hum no matter what tube I was using.
Hi Kratos
I have the same behaviour exactly with my adapter. When using 6SN7 tubes I set the Crack volume to maximum and control the volume through my preamp.
Hi wOlfdOg,
It's weird, because I am the opposite to you. I set the 'preamp' volume ( Foobar volume ) to maximum and then control the volume through my Crack. So I just needed to turn to about 9 o'clock to reach my preferable volume level.
I guess I'll clean up the tube pins and try it again.
So we have possibilities of the tube or the adapter. I'll throw in another variable, short the inputs with jumpers or shorting plugs before testing hum.
It could be the interconnects. It could be that it was there but the new tube brought it out. So you need to eliminate anything before the Crack.
Hi Grainger,
The hum was still there even without the source. So it can't be the interconnects. As soon as I turned the volume pot to 11 o'clock, the hum appeared.
Best,
Kratos.
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Hi Kratos
I have the same behaviour exactly with my adapter. When using 6SN7 tubes I set the Crack volume to maximum and control the volume through my preamp.
"Hi wOlfdOg,
It's weird, because I am the opposite to you. I set the 'preamp' volume ( Foobar volume ) to maximum and then control the volume through my Crack. So I just needed to turn to about 9 o'clock to reach my preferable volume level."
This is what I would normally do, except when this dodgy adaptor. My method results in no hum. A workaround.
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Also, what did you mean by wire the Crack to use 6CG7/7AU7?
If you break the connection at pins 4/5, then move the black wire from pin 9 to the unoccupied pin (4 or 5) on the 9 pin socket, then you can use the 7AU7. This will also allow you to plug in a 6CG7, which is roughly equivalent to a 6SN7.
-PB
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Thanks, PB. I think I'm going to leave it as-is. I'm very happy with how my Crack sounds with 12AU7s. The 6SN7s were an experiment. If the next adapter doesn't work, so be it.
Unless I decide to build a separate power supply for the 6SN7...
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The volume control behavior suggests that there is some electric field coupling capacitively to the grid of the 6SN7. When the control is at either end, the impedance to ground is low so the high impedance of the capacitive coupling is shunted to ground - but at maximum impedance (around 3/4 of the way up for a logarithmic volume control) that interference does create an audible grid voltage.
My guess as the likeliest culprit is a grid wire inside the adapter is too close to a heater wire.
If anyone has a pile of adapters including the reverse (use 12AU7 in a 6SN7 socket), you could stack two so you test the 12AU7 with and without adapters, to prove whether it is the adapter or not. A 6-volt wall wart power supply feeding DC to the 6SN7 heater would also determine whether the heater power is the source. These are diagnostic suggestions, not long-term solutions of course.
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The volume control behavior suggests that there is some electric field coupling capacitively to the grid of the 6SN7. When the control is at either end, the impedance to ground is low so the high impedance of the capacitive coupling is shunted to ground - but at maximum impedance (around 3/4 of the way up for a logarithmic volume control) that interference does create an audible grid voltage.
My guess as the likeliest culprit is a grid wire inside the adapter is too close to a heater wire.
If anyone has a pile of adapters including the reverse (use 12AU7 in a 6SN7 socket), you could stack two so you test the 12AU7 with and without adapters, to prove whether it is the adapter or not. A 6-volt wall wart power supply feeding DC to the 6SN7 heater would also determine whether the heater power is the source. These are diagnostic suggestions, not long-term solutions of course.
In my mind it is definitely the adaptor. I have tested thirty odd 6SN7s with the same outcome in each case.
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Have any of you considered installing an Octal socket? Not hard to do.
If I was considering the 6SN7, and I would. That's what I would do. Give it a fair chance.
We can help...John
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Have any of you considered installing an Octal socket? Not hard to do.
If I was considering the 6SN7, and I would. That's what I would do. Give it a fair chance.
We can help...John
No kidding. I would've changed the socket if I were going to test 30 tubes.
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Have any of you considered installing an Octal socket? Not hard to do.
If I was considering the 6SN7, and I would. That's what I would do. Give it a fair chance.
We can help...John
No kidding. I would've changed the socket if I were going to test 30 tubes.
Hah - Didn't buy the tubes to test the Crack. Had the tubes anyway. Thanks for your suggestion though.
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Adapter #4 was the worst of them all in terms of aesthetics (ugly as sin), build quality and usability. It took me about 40minutes just to get one of my 6SN7s into the adapter, because either the holes are slightly too small, or the pins are too tight.
Once I got the 6SN7 inserted far enough, I plugged it into my Crack. Same problem as with the others. Four adapters, and far too much money and frustration later, I'm done. I have plenty of 12AU7s and related variants I can use in the Crack, and I love the way they sound, so I don't even know why I went down this 6SN7 detour. I'll save my 6SN7s for my other amps.
Yes, I know that putting in an octal socket would be fairly easy, but its just not worth the effort to me. I'll stick with the stock socket and 12AU7s. Now I just need to spend another hour or so trying to get my 6SN7 out of that #%^
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You can heat the driver tube with a DC supply, and your socket noise issues should go away.
-PB
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So no one has found an adaptor to use 6SN7's in the 12AU7 socket with no added hum/noise, huh?
If anyone has, a link would be appreciated.
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Some folks do claim that they have noise-free 6sn7 adapters, but my experience has been the same as Adam's. Granted, I gave up after two failed attempts.
My second adapter (from lowther), was way better than the first but still noisy enough that my ears felt considerable relief when I switched back to a 12au7.
It may also be that the frequency of the noise is a lot more audible to those of us who primarily use our cracks with hd800's. When I have a chance, I'll bust out the better of my adapters again and try it with my hd650's. Their polite trebles may well serve to mask most of the noise.
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Thanks Mike. I have Hd650's and may have a chance to get some 6SN7's for cheap, but I'd prefer not to spend the $15-20 on the adaptor if it's just going to be noisy.
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It sounds like that if you like the 6SN7 over the 12AU7 you should put in an octal socket and convert. There are others who have done this and have had no noise problem. After all, all wiring is under the chassis plate and soldered.
Then maybe a 6SN7 to 12AU7 adapter will be quieter.
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I'll repeat (for about the 3rd or 4th time) that heating the driver tube with DC will eliminate the noise issue of these adapters, and can be done very inexpensively.
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PB - that was my original understanding, but in response to one of my posts in the crack thread on headfi (as "skeptic"), I understood Doc as saying that ac shouldn't really be an issue for purposes of using adapters. (see posts 1532-1533 https://www.head-fi.org/t/476650/crack-bottlehead-otl/1530_30#post_9222640 )
Have you guys had a chance to do any in house testing on this? If so, it would be great if someone would post a dispositive conclusion on HF to end any remaining confusion on this point.
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I don't think we have any adapters in the house. I think we were hoping that someone who had the adapters would rummage around the house to find a 6.3V wall wart to give it a try.
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Out of curiosity (I'm really not inclined to spend any more time on this experiment, since I'm perfectly happy with my 12AU7s), how exactly would this work?
1. Would the adapter have to be exactly 6.3V, or would 6V suffice? When you first mentioned this, I looked around for 6.3V PSUs and didn't find any (I'm not saying there aren't any, just that my quick search didn't turn up any at the time, other than DIY options).
2. What modifications would be necessary? I assume I would have to remove or clip two of the pins from the bottom of the adapter (and maybe cover up the clipped pins to avoid any risk of electrical contact with the relevant holes in the Crack's 9-pin socket), and wrap the exposed leads from the PSU around two pins in the 6SN7 before inserting it into the adapter?
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1. Would the adapter have to be exactly 6.3V, or would 6V suffice?
2. What modifications would be necessary?
Look for wall warts that are 6-6.3V and rated for at least 300mA. Something like this (http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_101266_-1) will work if you need to buy one.
To modify the Crack, snip the black/red pair of wires leaving pins 7/8 of the octal socket and heading to the 9 pin socket. Snip them off at the octal socket. Strip the wires back and solder them to the wall wart cord (cut the plug off, strip each wire back). Heat shrink the joints. It doesn't matter which wire is connected to the red, and which to the black when you're connecting the wall wart.
There's a very, very slight possiblity of needing to add a ground reference to the 12AU7's heaters, but I wouldn't worry about it unless you get unusual amount of hum.
-PB
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Ahhhh....OK, so the mod has to be made to the Crack itself. In that case, I'm definitely out. I'm happy with my Crack as-is, and with all of my mods, making any further changes would be a major undertaking.
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Adam,
If you have a Wall Wart that is 6V@1A it will float high with a lower load. These are not regulated power supplies. But if you use 6V instead of 6.3V I think you are still within the range of what was specified.
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Thanks, Grainger. But I'm just not interested in making any changes to the wiring in my Crack itself. I now have those oiler motor run caps installed upside down on the top plate, so flipping it over is a more involved process than in the past, and each time I open up the Crack I have to desolder the leads to my coupling caps and...and...and it's just not worth it to me. I have zero complaints about my Crack when used with 12AU7s. Trying 6SN7s would have been a fun distraction, but it's really not necessary and the prospects of significantly improving on my current setup seem low.
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(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FROLF.gif&hash=d8c25de5059c9863b539eef0d5a5f9c5fb975e51)
I get a good mental picture of the problem. Your avatar helps too.
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Not a 6SN7, but using the earlier 6F8G with a very high quality adapter. Works beautifully, & sounds wonderful.
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Where did you get the 6F8G adapter?
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I wouldn't really like to mention a competitors name on a manufacturers forum, but if you Google '6F8G adapter usa' it should lead you to it. They are made with high quality teflon sockets, gold pins, not cheap but much better than any of the ones out of China.
Can also be made to order in any configuration you want.
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Just wondering if anyone has tried this method yet? (Using a DC adapter to heat the tube)
I have same problem as the OP. I'm using a 6SN7GT (Raytheon VT-231), and this adapter I bought off e-Bay: http://www.ebay.com/itm/1-convert-tube-socket-12AX7-12AU7-to-6SL7-6SN7-9-pin-to-8-pin-/281031554093?_trksid=p2054897.l5658 (which looks exactly the same as the one somebody else said worked fine for them)..... I can hear music with the adapter and the 6SN7 adapter connected, but there is a very loud staticky noise (about 60% as loud as the music at listening volume), mainly coming through in one channel (but easily discernible in both).
I've seen no definitive answer about how to get a 6SN7 working with my Crack (which has Speedball installed too). Works perfectly with 12AU7 inserted. I'd be willing to try modding it to support the 6SN7 but not unless someone is able to confirm it works, or at least draw some kind of a diagram for dummies (which I am in the context of this DIY audio world).
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I'am using a old desktop power supply and voltage regulator to heat my 6SN7 it is quieter than those eb4y adapters most of those are noisy i've been using this method before the crack.
(http://)http://cdn.head-fi.org/9/94/900x900px-LL-94f07ae2_DSC_3218.jpeg
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Hi you post a link to the socket you used in the conversion to swap out the 9 pin to an 8 pin?
Thanks
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Hi Adam,
I assume you ordered this adapter, right? http://www.ebay.com/itm/1x-6SN7-to-12AU7-Vacuum-tube-adapter-socket-converter-/300943315564?pt=Vintage_Electronics_R2&hash=item46119e926c
Try this one : http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=320659633166&ssPageName=STRK:MEWAX:IT#ht_1080wt_793
It looks cheaper and not as 'well-made' as the one you ordered, but it works well :)
Best regards,
This is a bad adapter. My crack sounds blur... Anyone have a parameter to build a better adapter?
Kratos.
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I'll repeat (for about the 3rd or 4th time) that heating the driver tube with DC will eliminate the noise issue of these adapters, and can be done very inexpensively.
So, I also wanted to try a VT-231 and bought an adapter. There is indeed a noise issue for me as well, but at a very low level. I think I would like to try the DC heating solution. My question is: would it be possible to put together a rectifier to rectify the AC coming from the crack transformer, or does it have to be an additional transformer or wall wart? Thank you!
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Just use the wall wart to be sure it's what you need. If the wall wart works, then we can discuss how one might get 6.3V DC inside the chassis.
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Ok, working on it! :) Thank you!
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The wall wart arrived, and I tried as you suggested. Unfortunately, this did not have any effect on the hum (which strikes me to be not so low anymore as I described previously). All my 12au7 are dead quiet and sound beautiful. Should I abbandon this experiment, or do you have other suggestions?
No worries, this is not life or death, just playing :)
Thank you!
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That's a bad sign for the adapter if a DC wall wart didn't help you out! Do you have a link to the wall wart you used?
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Yes, you can find it here. Was I too cheap?
http://www.ebay.de/itm/201201010078?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
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Maybe I should describe a bit more carefully what I hear: It is a hum loud enough to be heard at listening levels. Without any RCA cables attached, you can clearly hear it and it scales with the volume level. At loud levels you hear 120 Hz I guess + some higher frequencies, like you would hear from a sawtooth or similar. I use a step attenuator. Curiously, sometimes certain steps jump up to a much louder hum. If you step up and back, it might return to back to a lower level hum. This unsteady behaviour gets better the longer the tube is running. I tried 2 different 6SN7, both have the same problem.
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I don't believe it's a matter of price, as much as luck. If you search around on the forum, there are a few who have had success with these adapters, and they have posted information about the working parts.
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it scales with the volume level...sometimes certain steps jump up to a much louder hum. If you step up and back, it might return to back to a lower level hum.
Your attenuator is the problem.
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Thank you very much, Paul and Dan! I think under these circumstances I will stop experimenting with 6SN7 and be happy with the wonderful sound of my 12AU7.
I started this experiment because I did not like the sound of my TS 5998. But I found out that this was caused by the film cap I used to bypass the last cap of the power supply. After removing it I had wounderful, spacious sound. That happens if you try to improve something that is great without really understanding it - not every upgrade described is really an upgrade, I mean other than in price per pound :)
Just out of curiosity: if it is the attenuator, why can I hear the problem with the one type of tube, but not with the other?
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I am going by your description. Somewhere there is a bad ground connection or maybe a leaky heather/cathode interface. Turning the attenuator affects it. So either it's the attenuator contacts not making good contact or the tube - either its pin contacts or something internal - is being affected by the mechanical vibration created in the chassis by the clicks of the attenuator switch. The stock pot might not set the problem off, but of course we can't know that unless you put it back in.
The short story is if it was on my bench I could probably tell you exactly what is going on in a few minutes. But when a circuit has been modified in a multiplicity of ways and we have to rely upon written description rather than hands on testing the best we can offer is educated guesses. This whole notion of being able to talk a person though troubleshooting on a forum didn't even exist 25 years ago, and though we are pretty good at it, it's still a rather awkward and uncoordinated method of fixing something. At least it is far better than trying to troubleshoot over the phone.
I know we seem a little impatient at times trying to help people who - from our perspective - decide to improve our products, but find that the circuit does not work right after they do. That may be rooted in the fact that we spend a lot of time deliberating over an aspect of a component that is often not understood by those who substitute other parts, and we (mostly meaning Josh these days) also spend a lot of time making the assembly manual as specific as possible to guarantee proper function. Everyone hates it when we say "return the circuit to stock". But it always works right if you do, and we will know exactly what you are looking at on your bench when you need assistance. At the same time this is DIY and we believe strongly that people should experiment and learn. That includes learning how to systematically go through something that isn't working as expected and using some logic to eliminate possibilities until you arrive at a solution. Changing one thing at a time is a very good way to maintain control in the modification process, and being willing to go back to where you were before the problem started to help identify what is going on is a very good habit to have acquired. I laud your efforts in that direction.
To be a little more blunt about one aspect of this conversation - if the guys who sell those shitty adapters would support them, we wouldn't have to waste so much time trying to help people with them. This noisy 6SN7 adapter opera has been going on for years now. You would think by now they would have figured out how to make the damned things.
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That's one of the best post's I've read in a long time...John
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This thread motivated me to buy one of these "better" 6SN7 adaptors and it has been perfectly functional plus quiet in my crack. It is not from eBay and I believe it's American made:
http://bottlehead.com/smf/index.php?topic=7742.0