Tube choice in one-tube bass preamps (SWR, etc.)
Kurt Kurosawa
plugged up and hit the first note. No amount of knob twiddling could tame
the unruly sound, harsh up high, peaky in the mids, and big and blurry in
the bass. I figured the only part of the circuitry I could change was the
tube, and because my entire signal went through that one tube, I was
entirely at its mercy, so I started reading up on tubes, and considered
buying a Telefunken flat-plate diamond-base ECC83 (they go for $100 new and
$30-40 used). Expensive fix for a newish amp that I just paid $400 for! Then
I stumbled across this article (if you have a one-tube preamp in your amp,
like an SWR or Trace or Eden, you really need to surf over there):
http://www.audioasylum.com/audio/faq/joes-tubes.html
. . . and I learned all about the 5751 tube. It is an industrial tube with
only 70% of the gain of a 12AX7, and because it's not an audio tube, the
sound qualities differ greatly not only from make to make, but from lot to
lot. So who needs the hassle? Well, first I learned from Joe's FAQ that the
12AX7 is noisy and blurry. Actually, I knew that already, but it's good to
hear it from an expert. Then I learned that the three-spacer 5751 was
designed for toughness and survivability in B-52s and other nuclear war
weapons systems. Cool. Then they ought to do just fine sitting on top of a
thundering bass speaker. And lastly, I learned from the FAQ which ones to go
hunting for.
I went to a local electronics supply and they had piles and piles of tubes.
All the 5751 tubes were 10 bucks and new and used ones were all mixed
together, 13 in all. I picked out two, a government contract 1959 Sylvania
JHS 5751 with gold print, and a Sylvania Gold Brand grey plate (supposed to
be the cat's meow). The Gold Brand dropped out the bass (the notes from low
E to A, which had been balanced in volume with the others, were noticeably
quieter) and put an annoying peak in the midrange. I talked to another tube
expert, and he said, yes, it would take a month of playing for that
particular tube to break in and for the bass to come in properly. As it
turns out, that midrange peak is right where female vocals live, and it does
amazing magic with them, and that's why audiophiles love the tube, but it
was bad for me, so that tube went back in the box.
The Sylvania JHS 5751 gold print, on the other hand, was pure magic. It took
every bit of the harshness out of the highs on Pyramid Gold flatwounds (the
harshness of these strings makes a SansAmp PS-1 into a Stewart World 1.2
into an Epifani 410 sound bad). The sound of this tube was the sound of the
bass itself without the coloration of the "hand selected" Groove Tubes
12AX7A that came in the amp. I flattened all the EQ (actually, my EVM 15L
needs +6 dB bass, but really, the only thing EQ should be used for is to fix
the speakers and the environment, not the amp itself). I turned down the
Aural Enhancer all the way. And without any coloration masking my sound,
what I heard was the voice of my bass, the pure muttering growl of the
P-sound.
By the way, it doesn't matter to me that the 5751 only has 70% of the gain
of the 12AX7. The Bass 350 manual says to turn up the preamp gain knob until
the clipping light flickers as I play at my normal volume. For me, that's
about 2 o'clock for flatwounds or 1:30 for roundwounds, so the 5751 has
plenty of gain for my purposes. Maybe if you had a Dano or some other
low-volume axe, you might run out of gain. Maybe. But if you're doing like
the manual says and the light is flickering and the knob isn't maxed out, I
don't think you're going to notice the lower gain. Besides, the purpose of
higher gain is to increase the S/N ratio, and 12AX7 tubes are so much more
inherently microphonic than military three-spacer 5751 tubes, I think the
S/N advantage probably lies with the 5751.
Brad Johnson
Brad
>Subject: Tube choice in one-tube bass preamps (SWR, etc.)
>From: "Kurt Kurosawa" kurt-k...@home.com
>Date: 10/10/00 7:08 AM Eastern Daylight Time
>Message-id: <oMCE5.73213$j6.81...@news1.rdc1.va.home.com>
>
>I recently bought a minty '98 SWR Bass 350. I hated the sound as soon as I
>plugged up and hit the first note. No amount of knob twiddling could tame
>the unruly sound, harsh up high, peaky in the mids, and big and blurry in
>the bass. I figured the only part of the circuitry I could change was the
>tube, and because my entire signal went through that one tube, I was
>entirely at its mercy, so I started reading up on tubes, and considered
>buying a Telefunken flat-plate diamond-base ECC83 (they go for $100 new and
>$30-40 used). Expensive fix for a newish amp that I just paid $400 for! Then
>I stumbled across this article (if you have a one-tube preamp in your amp,
>like an SWR or Trace or Eden, you really need to surf over there):
>http://www.audioasylum.com/audio/faq/joes-tubes.html
>snip<
Scott
Kurt,
Nice story.I'll have to try some 5751's in my SWR Studio 220.I have
plenty of GE and Sylvania 5751's to experiment with.I do however,
use Telefunkin 12AX7's(I bought 5 or 6 used for $5.00 a piece..yeah I
know I got a real lucky find here)in my Studio 220.
The sound differance between the Telefunkins vs. Sovtek and Chineese
tubes(that I was using before)was HUGE!My Studio 220 instantly came
alive with the Telefunkin 12AX7's.The sound really blooms in the
mid-range.Actually it sounded as if I bought a new amp when I replaced
the Sovtek and Chineese tubes that I used to experiment with in my SWR
Studio 220.
Anyway.....even though the sound is greatly improved with the addition
of Telefunkin 12AX7's,I wonder if buying a bunch of new Telefunkin
12AX7's would be worth it.I mean for the price I paid for some used
ones....why not?But......new at around $75-$100 a piece I can't
possibly justify the expense!Even if the sound is far better.
Hmmmm.....I also have a bunch of GE,Sylvania,RCA,and Mullard 12AX7's
that I'll have to try next to see how they compare to the Telefunkins.
Scott
On Tue, 10 Oct 2000 11:08:04 GMT, "Kurt Kurosawa"
<kurt-k...@home.com> wrote:
>I recently bought a minty '98 SWR Bass 350. I hated the sound as soon as I
>plugged up and hit the first note. No amount of knob twiddling could tame
>the unruly sound, harsh up high, peaky in the mids, and big and blurry in
>the bass. I figured the only part of the circuitry I could change was the
>tube, and because my entire signal went through that one tube, I was
>entirely at its mercy, so I started reading up on tubes, and considered
>buying a Telefunken flat-plate diamond-base ECC83 (they go for $100 new and
>$30-40 used). Expensive fix for a newish amp that I just paid $400 for! Then
>I stumbled across this article (if you have a one-tube preamp in your amp,
>like an SWR or Trace or Eden, you really need to surf over there):
>http://www.audioasylum.com/audio/faq/joes-tubes.html
>
Kurt Kurosawa
Didn't have a chance to play it first, if that's what you're asking. Not a
great variety of used gear hereabouts.
Kurt Kurosawa
sadly out of production, get some before they go away (wish I could find the
URL of the review I read). Anyway, if you buy from Steve at angela.com you
will get the best price out there, and if you let him know you are a bass
player and are concerned about microphonics because you put your amp on top
of a bass speaker, he will pick one out just for you.
"Scott" <htal...@nycap.rr.com> wrote in message
news:39e32945...@news.nycap.rr.com...
Salo
You know, Warwick's new head Quad VI has actually 4
tubes in preamp, and a four-way selector on front panel for em.
And it gives 600w, so it's kinda neat.
-Salo
---
Let us play.