SEX tubes

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Offline Paul Birkeland

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Reply #45 on: December 03, 2014, 11:31:57 AM
You would not want to use premium 6SN7's in this application.  This is experimental, and likely will reduce the effective lifetime of the tubes used.

Paul "PB" Birkeland

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Offline i luvmusic 2

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Reply #46 on: October 17, 2015, 08:37:19 AM
 I finally replaced my 6H8C that i've been using for some time with this SYLVANIA 8SN7GTB i was not expecting much from this Sylvania 8SN7GTB but WOW!Sound smooth i'am loving it so far. ;D


Offline mcandmar

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Reply #47 on: October 17, 2015, 09:17:49 AM
8SN or 6SN?    If its an 8 its going to be running cold with low emission.  I ran a frequency response test on mine with a 6SN7 and i was not impressed with the results...

M.McCandless

Offline i luvmusic 2

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Reply #48 on: October 17, 2015, 09:35:40 AM
It's 8SN7GTB........I like it.


Offline boulos

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Reply #49 on: October 17, 2015, 10:38:38 AM
I haven't tried the 8SN7GTB, but I've gone back to the 6DN7 tubes a while ago.


Offline Paul Joppa

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Reply #50 on: October 17, 2015, 11:03:32 AM
The 8SN7 wants 8.4v heater power; it might be prudent to measure the voltage at the socket. If it's less than 7.5 volts, the cathode is not likely to last long.

That same voltage for the 6SN7 may be a little high due to the reduced current demand - worth checking if you are running these tubes long-term.

The low frequency extension (-3dB at 35Hz if I read the plot correctly) is probably affected by the higher plate resistance; experimenting with a larger parafeed capacitor might prove interesting. Was this measurement made with an 8-ohm load on the 8-ohm tap?

Paul Joppa

Offline mcandmar

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Reply #51 on: October 17, 2015, 11:14:39 AM
All tubes were tested on the 8ohm tap into a 32ohm dummy load.

M.McCandless

Offline dmhenley

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Reply #52 on: November 02, 2015, 01:55:25 PM
Quote from: Paul Joppa on October 27, 2014, 07:15:56 PM
So I fired up an old spreadsheet and looked more closely at the 6SN7-GTB. It should work just fine, and within spec. Output is about 3/4 watts, damping factor 1.0.

A speaker with a very low QT could work really well with the low damping factor; for example an FE-206E Fostex in a 1 cubic foot box tuned to 50Hz or a bit lower. Try a 2.5-inch ID tube 4" long. Parts Express has ready-made 1.0 CF boxes.

Alright, I'm in - I've got a pair of TS 6SN7GTB, and feel like experimenting.
You'll not find any measurements here - I'm a drummer, not an engineer - and, lack the necessary skills and equipment (fairly certain hitting the SEX with sticks will not help), but I'll log the hours and sound quality as I go.


Offline dmhenley

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Reply #53 on: November 04, 2015, 10:34:16 AM
Alright - after about 24 hours of play time on these new prod Tung Sol 6SN7GTB...
This comes out of extended listening, while working.

I perceived slightly more gain than the RCA 6DN7 I've been using. Kept the volume set while testing. More air/sparkle and perhaps more touch and presence in the mids. This may just be new vs old tubes? Or, maybe there's a subtle upper and mid forward shift combined with rolled off low freqs, with these 6SN7.

At times, I heard an unnatural edge (tizzy) on cymbals - not great. Over hours of listening, they generally sounded too lean and bright. This is something the amp excels at in its stock form, and in my system - natural sounding acoustic instruments. Could be this bright edge would subside with more time.

The low end is less extended and defined with the 6SN7. Pretty significant loss there.

Went back to the stock pair and it reminds me how much I like this amp.
All good. For me, this is the point - perspective.

I'll keep playing with the 6SN7 off and on - maybe more play time will help.
I am more interested in the coming cap upgrades.

I should add that the 6SN7 sounded good in general - not all bad.
Finally - the hum I'd battled with a minor mod recently was louder with these tubes.
« Last Edit: November 04, 2015, 10:54:17 AM by dmhenley »


Offline mcandmar

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Reply #54 on: November 04, 2015, 11:24:52 AM
You pretty much nailed it, have a look at the frequency response chart i posted further back in this thread, the low end with the 6SN7 drops off pretty dramatically from 300hz down.

M.McCandless

Offline dmhenley

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Reply #55 on: November 04, 2015, 12:35:53 PM
Quote from: mcandmar on November 04, 2015, 11:24:52 AM
You pretty much nailed it, have a look at the frequency response chart i posted further back in this thread, the low end with the 6SN7 drops off pretty dramatically from 300hz down.

Ah, maybe I'm learning! Regardless,  I am trusting my ears more as I go on.
Doing this little test drove me to purchase a couple Sylvania 6DN7 off Ebay.



Offline mcandmar

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Reply #56 on: November 04, 2015, 12:42:27 PM
The most rewarding is when you hear X, then measure it and find the same result :)

The Sylvanias (provided they are the real Sylvania and not rebrands) are the best sounding for mid/low end. You sacrifice a little bit of high end response vs the others, but depending on your setup that may be just what you are looking for.

M.McCandless

Offline dmhenley

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Reply #57 on: November 04, 2015, 12:58:14 PM
How do I ID the tubes as true Sylvania? codes?


Offline mcandmar

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Reply #58 on: November 04, 2015, 01:05:18 PM
Look at the construction, if the plates and mica spacers look like these they are Sylvania,

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fbottlehead.com%2Fsmf%2Findex.php%3Faction%3Ddlattach%3Btopic%3D5316.0%3Battach%3D5121%3Bimage&hash=75c3de065a6c0fbab513c8caf21e196a978803d6)

GE/RCA/TS look like this,

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fbottlehead.com%2Fsmf%2Findex.php%3Faction%3Ddlattach%3Btopic%3D5316.0%3Battach%3D5115%3Bimage&hash=e015779abdeac9d64c506c3482b6c4a6bbcbc4f2)

M.McCandless

Offline dmhenley

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Reply #59 on: November 04, 2015, 01:12:50 PM
Thank you!
I bought a couple - separately - as I only have 2 pair today.
I've been holding off because  based on all yours and others posts, there's not much sonic variety there.


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