Tuberolling 6SN7s with the Eddie Current HD-25
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adhoc

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Tubes reviewed so far:
• Sylvania 6SN7GT (1952 vintage)
• Raytheon VT-231 (clear glass, box-plates, not staggered plate version)
• Ken-Rad VT-231 (black glass, staggered plates)
• Sovtek 6SN7GT (new stock tube)
• Tung-Sol 'Round Plate' 6SN7GT (Oval Mica)
• RCA Red Base JAN-5692
• Sylvania 6SN7GTB small top getter yellow labels
• Channel Master 6SN6GTB (new stock tube)


Headphone used- Grado RS-1

Introduction:
The Eddie Current HD-25 is a tube amplifier (with a transformer, not an OTL design) that uses 2 tubes - 1x 6SN7 (or compatible) and 1x 6AS7 (or compatible). On the advice of Craig Uthus of Eddie Current, the tube that influences the sound the most would be the 6SN7. The 6AS7, being transformer plate coupled, also does affect the sound somewhat - opinions on this tube are more than welcome in this thread too.

As the HD-25 uses a single 6SN7, unlike other amps, one is unable to mix a trio or quad of 6SN7s to get that 'perfect' sound. This presents us with a unique experience - 1. we do not need to bother with obtaining matched pairs of tubes and 2. as long as we do not vary the 6AS7, we are able to listen to what the various 6SN7s really sound like.

Hence this thread.


FWIW, the amp is turned on for at least 3 hours to warm up before I first start listening. All tubes are given at least 10 mins to warm up before plate voltage is applied. The HD-25 has been run for over 300 hours now, so I’m quite sure it’s fully burnt in. There is no hum/sizzle/crackle/pops/whines with the supplied 6AS7 [actually a nos metal base RCA 6080] that Craig supplied me. OK, enough said - on to the reviews!


Sylvania 6SN7GT (1952):
A tube with what is imo a slightly dark and effortlessly natural sound. An extremely sweet (but not overdone) midrange. There is roughly the same amount of slam as the Ken-Rad VT-231 [KR], yet the slam is definitely less visceral than the KR. This is an extremely musical tube, with a less airy sound than both the KR and Raytheon [RT]. The treble on this tube is more ‘tubey’ sounding, and is less cold than the KR and certainly the RT. What surprised me was that there was slightly less discernable low level detail than the KR. Low level detail is the same as the RT. Instrument separation was slightly less than the RT. A completely non-fatiguing tube to listen to. Female vocals are a joy to listen to on this tube – echoing another member, I really feel like reaching across and getting to know Diana Krall a –whole- lot better with this tube.


Obligatory analogy – You’re watching a sunset on beautiful tropical island – the waning light makes details a bit difficult to discern, but the view, with the rolling sea and lush greenery bathed in a sienna glow, is indescribably beautiful. It’s also just starting to get a bit dark.



Ken-Rad VT-231:
This is a tube that I enjoy immensely. Bass is very propulsive and visceral and grabs you at first listen. Unexpectedly, low level detail is best of all the tubes tested so far. I had my sister randomly switch tubes while I was blinded and I confirmed, in my setup at least, that this tube is the best for low level detail. Midrange is slightly less sweet than the 1952. Bass slam on this tube has to be heard to be believed. Instrument separation is slightly less than the RT. Vocals are a nice blend of clear and sweet on this tube. A very quick tube, outdone only by the 1952.

Obligatory analogy - You’re done with the romantic sunset. It’s time to let your hair down. This is a beach club (well-lit by kerosene lamps) with ice-cold beer, mirror balls, lasers and a killer DJ spinning some deep trance. Time to PAAAAARRTY the night away!



Raytheon VT-231:
Compared to 1952 and KR, this is a brighter sounding tube. There is a certain forcefulness to the presentation that is quite attention-grabbing. Vocals are extremely clear with this tube. The mids are less sweet and a wee bit thinner than both the KR and 1952. There is a slight dry-ness to the sound overall. Clarity clarity clarity, yet less low level detail than the KR. A tad less bass slam than the 1952. I noticed some reverb.

Obligatory analogy - Bali on a ridiculously hot day in May. Everything is clear under the scorching sun, yet perhaps some of the romance is lost at the same time with all that heat.



Sovtek 6SN7:
The Sovtek is stock with the HD-25. Being a universally panned tube, I expected little of this tube...

...only to have it surprise me. Now, this tube is by no means a match for any of NOS tubes I've reviewed so far, but if one were hopelessly strapped for cash or for some reason unable to obtain any NOS tubes, one could conceivably survive comfortably with this tube.


This tube has an extremely forward and big bass, a moderate amount of slam, a too-rich sounding midrange and slightly recessed highs. Mids are a bit shouty-sounding. Where this tube fails, and fails miserably, is details and seperation. When compared to the 1952/KR/RT, everything seems hopelessly smeared. There is less 'air' around instruments than both the 1952 and RT.

Obligatory analogy – You’ve just drunk too a wee bit too much at the hippest nightspot in town. All you hear is the thumping beats, all you see are smeared flashes of coloured lights. Your can see your friends talking to you, but they seem and sound a little distant.


Tung-Sol 'Round Plate' 6SN7GT [oval mica - circa 1943-46]:
This tube seems to do everything well - detail? check. bass? check. impact? check. musicality? check.


This tube seems to have a slightly dry signature when compared directly to the Syl '52. It seems to combine the best traits of many tubes - the bass and impact of the KR VT231, the clarity of the RT VT231 and most of the musicality of the Syl '52 with unparalled detail. This tube makes music, any music, beautiful to listen to - it certainly lives up to its reputation.

Obligatory analogy – A night out at the Royal Amsterdam Concertgebouw hall with the Philadelphia Orchestra playing: a hall known for its slightly dry sound signature and ability to discern detail paired with an orchestra famous the world over for 'the unbelievably lush philadelphia sound'.


RCA Red Base JAN-5692:
Warm. Lush. Romantic - these words spring to mind immediately. Better air than even the TS RP. Seperation and detail are on par with the best of them imo. Slightly tubby bass. Good impact. Amazing with jazz and pianos. Never harsh sounding.

Obligatory analogy – It's date #3, and you're beginning to feel comfortable with her. No more awkwardness, no more nervousness - you hold her hand and look into her beautiful eyes at a romantic candle-lit dinner... Ah, bliss.



Sylvania 6SN7GTB small top getter yellow labels:
Surprisingly refined sounding - not bad considering the bargain prices these can be picked up for. Great detail and air. Cymbals have a very nice shimmer to them with this tube. Very very slightly dry sounding. Not too much impact. Bass seems a tad moderated with this tube compared to, say, a Ken Rad vt231. Great extended decay on notes. Laid-back sounding.

Obligatory analogy – This is a difficult one. Somehow I keep returning to an image of a quiet evening spent indoors lazing on a pile carpet on a cool, rainy day watching the water streak down your windows...



Channel Master 6SN6GTB (new stock tube):
Somwhat blurry sounding. Nothing special about this tube - it has an inoffensive laidback sound. Recessed highs. Some strange reverb. Very tubby bass. Not much air.
 
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ayt999

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that's the Bad Boy right, the Sylvania 6SN7GT (1952). just making sure.
 
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Jon L

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6SN7 rolling is like drug addiction. It 'should' be outlawed but is irresistable. I would hate to total up all the $$$ I've spent over the years collecting 6SN7/VT231 types.

The problem, as you know, is finding THE ONE, the end-all-be-all 6SN7, especially if you can't mix and match. Also, 6SN7's LOVE Herbie Tube Dampers, and some very old, microphonic 6SN7 types almost transform w/ the Herbies, so if you don't have one, you should try to get one.

I would say forget about GTB types, RCA or GE, unless you Really can't afford others. Hope you have the following worthy contenders to try out:

Sylv VT231 old fave
TS roundplates overpriced fave
TS 6SN7WGT dark horse
CBS/Hytron 6SN7GT darker horse
RCA grey glass interesting comparison to KenRads
Sylv 6SN7W plastic base REALLY oldie
Sylv metal base touchy but in the right setup will go ballistic
National Union Black Glass more available than grey glass but
National Union Grey Glass my fave w/ Herbies (contact me if you have some)
 
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adhoc

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testing out the ken-rad vt-231 now.. when i'm all ready i'll amend the original post with my complete opinions - for now, some very brief impressions.


this is an excellent tube. i think i may prefer the highs on this to the syl '52. when someone thrashes a cymbal on the ken-rad, it makes me wince. this does not happen with the syl. but doesnt a cymbal thrash in real life make one wince?


EDIT: omg, did i forget to mention something about the bass? oh, the bass! the bass!
 
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Jon L,
Personally I would not rule out the RCA's that swiftly, and I am talking about the black-plates from the 40's and on to the early 50's.

Everybody is talking about the grey-glass till 1948, and they are very nice, but IMO, and I really like these RCA's
, the clear glass are also very good, having a bit more sober quantities of what makes the grey-glasses so appealing. Actually the very earliest GTA's are worth attention too, but then for other reasons


EDIT: Ooops, I was talking about RCA 6SN7 in a MPX3. I wouldn't know the sound signature in an Eddie Current. Sorry...
 
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Jon L

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Quote:

Originally Posted by Glod
Jon L,
Personally I would not rule out the RCA's that swiftly, and I am talking about the black-plates from the 40's and on to the early 50's.

Everybody is talking about the grey-glass till 1948, and they are very nice, but IMO, and I really like these RCA's
, the clear glass are also very good, having a bit more sober quantities of what makes the grey-glasses so appealing. Actually the very earliest GTA's are worth attention too, but then for other reasons


EDIT: Ooops, I was talking about RCA 6SN7 in a MPX3. I wouldn't know the sound signature in an Eddie Current. Sorry...




Of course not! I'm just talking about the RCA orange label 6SN7GTB that Adhoc mentions..
 
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Mikey01

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Quote:

Originally Posted by adhoc
Tubes that i've 'reviewed' so far:
· Sylvania 6SN7GT (1952 vintage)
· Raytheon VT-231 (box-plates, not staggered)
· Sovtek 6SN7GT



But how do you like the sound of the HD25 in general? How does it compair to other amps you have owned or heard?
 
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adhoc

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Jon L, wrt herbie's hal-o's:

fwiw, with no music playing and the volume maxed out, i hear nothing. how would hal-o's help me in this case then?
 
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adhoc

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Quote:

Originally Posted by Mikey01
But how do you like the sound of the HD25 in general? How does it compair to other amps you have owned or heard?



Mikey01,

the hd-25 is my first tube amp i have owned and/or spent a considerable amount of time with, so while i may have heard other tube amps (a melos and a cary) i would not be able to make a fair comparison to these other tube amps as i simply

but in fairness, what i can say is that the eddie current hd-25 is lightyears ahead of my headsave classic. the poor classic (dual opa627) is trounced in all areas. when i go back to it now it sound dry, uninteresting and lacks dynamics. to use an analogy, i feel like someone who has been seeing in black and white his entire life and now sees in colour. i guess the classic is now relagated to my sister's rig to amp her hd 25-1s.


the hd-25 has no problems whatsoever powering my grados to painful volumes while maintaining coherency. everything sounds exactly the same at all volumes. i have yet to hear this amp clip with my grados. fwiw, you can only hear the external transformer hum if you literally press you ear against its enclosure, and even then, it is barely audible. everything is solidly built and well put together. switches and knobs have a great feel to them. even though my amp was an ex-demo piece, i'd bet you wouldnt be able to tell!


in addition, i've come to realise that i can really never be sure whether what i'm hearing is due to the tube or the actual amp.
 
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Jon L

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Quote:

Originally Posted by adhoc
Jon L, wrt herbie's hal-o's:

fwiw, with no music playing and the volume maxed out, i hear nothing. how would hal-o's help me in this case then?



Herbie's are for killing microphonics, which has nothing to do with resting background noise levels. Tubes, especially old NOS, tend to "ring" (aka microphonics) when there's vibrations reaching the tube. In bad cases, just ligtly tapping the component or equipment rack will cause microphonics, which you can hear through speakers as ringing, pinging, etc. In really bad cases, if you just speak near the tubes ("speaking to tubes"), you can hear something resembling your voice coming through speakers.

Now, most good-testing tubes don't have microphonics nearly as bad as that, but even the most modern, quiet tubes have Some microphonics. Obviously, this effect will be most audible with speaker systems when everything vibrates, but even in headphone systems, moving parts of CDP, subtle vibrations of transformers, etc, can cause subtle microphonics.
It's really hard to describe what exactly microphics sound like, but once you put the Herbies on, you will 'know.'
 
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My favorite tube has been a GE 5998A in place of the 6AS7G. Everything improved significantly except for bass slam, but I think the bass was pretty muddy with the stock tube.
The Sylvania 6SN7GTA (1955 I think) is similar in flavor to the stock tube, but just better, especially with imaging.
The RCA VT231 (late 40's) is warmer than the others with a little less detail than the sylvania, but sounds more natural with some music, especially female vocals.

My next tubes will be a WE 421A and a Tungsol VT-231 whenever I can find them.
 
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adhoc

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Quote:

Originally Posted by S_Dedalus
My favorite tube has been a GE 5998A in place of the 6AS7G. Everything improved significantly except for bass slam, but I think the bass was pretty muddy with the stock tube.
The Sylvania 6SN7GTA (1955 I think) is similar in flavor to the stock tube, but just better, especially with imaging.
The RCA VT231 (late 40's) is warmer than the others with a little less detail than the sylvania, but sounds more natural with some music, especially female vocals.

My next tubes will be a WE 421A and a Tungsol VT-231 whenever I can find them.



please post your impressions in this thread!

fyi, all impressions in this thread will eventually be added to the 6SN7 Reference Thread, so dont be shy! the more, the merrier!
 
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adhoc

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Quote:

Originally Posted by Jon L
Of course not! I'm just talking about the RCA orange label 6SN7GTB that Adhoc mentions..


Jon L, what did you find wrong with these tubes in particular?
 
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adhoc

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ok, major changes done to the original post and the KenRad VT-231 review has been added.
 
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Hey, great impressions! The analogies are really fun, I couldnt write like this about my tuberolling experiences.
 
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