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FS Rare GE "Glow Dome" 6SN7 tubes


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Through my research and development of the forum amp I have been working on I dug out some 6SN7's for breadboarding the circuit. I planned on using the 6SN7 as a driver tube for the KT88/6550. Anyone that's into simulating circuits knows that the tube models are not accurate at all for grid current region of operation so I needed to do all my research with good old fashioned way. I ended up swapping from 6SN7 to a 6BQ5/EL84 as a driver due to it being able to drive grid current better than the 6SN7 did. I also tried a few other types but as of now the winner is the 6BQ5/EL84.

 

Since I tested a bunch of the 6SN7's and have them out already I figured I might as well get rid of a few to some forum members and spread the love around.

 

These will be in precision matched pairs or quads if people want. They are first screened for noise, gas, shorts and transconductance. Then they go into a real test circuit and precision matched for gain and distortion. Out of 47 I culled the ones that were not balanced between sections, or if they were noisy etc.. and put together a total of 6 pairs that are premium specimens that I will part with. Premium meaning they are balanced sections, dead quiet and zero heater leakage current seeping through into the cathode which shows up on an FFT spectrum analysis, basically if someones amp uses AC to power the heaters tubes with heater current leakage can cause 60Hz hum induced into the signal causing excess distortion. These are also ones that test for low distortion meaning they are the most linear of the bunch. I grabbed a bunch of these a long time ago because of two reasons, one I really loved how they looked with the filament strung across the clear top of the tube that glows when in use, hence why they are called "glow domes". But secondly I was very impressed with how well made these tubes are and how well they perform and sound, I hands down think they are some of the best out there. I have tested a bunch of Sylvania "chrome domes" and they on average have higher distortion and noisier than these, I was never really impressed with the performance of "chrome domes", I think people just purchase them because of the buzz around them like so many things in this hobby. I rarely see these types, I tried to get a look to see what they are selling for and few I saw were listed for $132/pair. I am not asking that high of a price of course. One of the listing says these only made up about 2% of the 6SN7's GE made so that explains why they are hard to come by. I guess I lucked out getting a bunch of them :D

 

Feel free to message me if you are interested and I can make up any amount for you in multiples of 2. They will be shipped Priority with tracking unless you want a different shipping method.

 

$70/pair shipping included with price

 

$120/quad shipping included with price

 

 

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5 hours ago, jcmusic said:

Curious as to how they sound compared to other 6SN7 tubes?

 

I have had quite the collection of 6SN7 tubes, probably every single type you can think of. To be honest with enough from each manufacturer I could screen certain brands to sound practically identical. For example I typically screen and pick the lowest distortion for hifi out of any brand but on average some brands test better/worse on average. For example the Sylvania types people love on average test a little high in distortion but I could still find some that test low or high. I think people like them because of the distortion, predominantly second harmonic. I have enough of these tubes to go through and pick some with slightly higher distortion figures if you like coloration.

 

If you can't tell I am not great at subjective descriptions. I typically deem how good a tube is if say I test 50 of them and if they aren't all over the place I know the manufacturer has the process down well and the tubes are very consistent, that to me is a good sign of quality. I was testing Amperex 12AU7 tubes and they are all fairly close on average and there are less problem tubes that I won't sell. Compare that to say the RCA "clear tops" which were more erratic in testing and less consistent. It doesn't mean you can't find a great clear top but on average they are going to differ in performance from one tube to another.

 

These 6SN7 tubes were pretty darn consistent and it was pretty easy to get 12 tubes to match up very well. As for subjective sound, I do not have an amp that uses them at this moment but when I was using a 6SN7 amp I chose these over many other types. They were not "sterile" by any means but accurate, still the lovely 6SN7 linearity it's known for which is accurate, tight bass and clean treble, pretty much what I want in a tube. But like I said I could go back and pick some out that tested higher in distortion and they will have more coloration.

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