SWR guys, Pre amp tube selection ?

[AdamR]

Just picked picked up a SM500, the previous owner said he had it for about 10 years and hasnt changed the tube. I figure its about due.

Are there any preferred tubes amongst the SWR camp ?

I would prefer some with a gritty mid range to it although Im not really sure changing 1 pre amp tube is going to make a huge difference in tone.

[JimmyM]

while 12ax7 tubes are cheap, i did a little bit of tube rolling with my old sm-500 once and noticed no tonal changes. of course, i never do, so i may not be the one to discuss it

but if the tube is working now, it will work tomorrow and probably the next day. tubes don't just automatically go bad after a year, or 2 years, or even 10 years. some can last decades.

[wvbass]

I have changed tubes in my redhead twice. I do it when I notice a little extra noise through the tweeter. First time, I put in the Chinese groove tubes 12ax7c. Supposed to be a cheap tube, and doesnt cost much. Sounded fine to my ear, and to others. Lasted about five years before it got noisy. Just put a groove tubes ecc83 in it; there might be a little more low end, but if there is, it isnt dramatic. But, i dont have the noise of the old tube anymore.

Im not sure you are going to notice significant changes, reardless of what tube you use. But I am sure the law of diminishing returns is in full effect here.

[Jim C]

I too rolled a number of tubes through a SM400 and also heard very small tonal differences; it seems the SWR's aren't particularly responsive to tube brands
FWIW, the one that was a bit better than the rest was a used original Mullard
Couldn't hear any difference between NOS Sylvania, GE, or Sovtek, Groove Tubes, EH, etc.

[mdogs]

Agreed, I can't hear any difference with the brand of tube in my SM-400. I did lose punch a couple of gigs ago and I was perplexed as to the problem. Finished the gig, plugged the amp in the next day and there was a ton of noise and ugly sounds(uglier than my playing!) then I realized it must be the tube. Replaced it (Russian GT) and like new again.

[JimiLL]

I just put a Telefunken in my Bass 350 and it cleaned up the sound a little; more clear.... and it might have boosted the low end a little bit

[will33]

Originally Posted by Jim C

I too rolled a number of tubes through a SM400 and also heard very small tonal differences; it seems the SWR's aren't particularly responsive to tube brands
FWIW, the one that was a bit better than the rest was a used original Mullard
Couldn't hear any difference between NOS Sylvania, GE, or Sovtek, Groove Tubes, EH, etc.

+1

I used my old Mullard in mine because it was slightly "thicker" sounding but the differences are pretty small. It'll sound like itself with pretty much any functioning tube. If you're buying a new one, I'd just get something that's known to be of good build quality, reliable, etc. and you're set for another 10 years. Preamp tube rolling can make a pretty noticable difference in some amps but not that one.

Actually nowdays, most of the tubes come from a very few manufacturers and mostly just have different labels printed on them so pretty much anything will work.

[JimmyM]

this is not to say the sm-500's tube is a show tube. you can get some nice preamp distortion with it, and i believe it positively affects the clean tone, too. but yeah, not a whole of variance between different tubes.

[12bass]

IIRC, the active input bypasses half of the tube, so use the passive input to use both triode sections.

[will33]

Looking at the manual, the front end operates the same as my 400. http://www.swrsound.com/support/manu...s/SM500_OM.pdf

I was making sure it didn't have pre and post gain controls as then a preamp tubes breakup characteristics would be a contributing factor but alas, it doesn't. Thought it was a little funny how they recommend getting the most "pure-tube overdrive sound"........ie: put another preamp between your bass and this amp and crank it.


From the manual:

B. GAIN - Adjusts the signal level of the
preamplifier. Equalization, tone and effect levels
all contribute to the preamp signal level therefore
Gain should be set after they are adjusted. (Gain
also controls the Effects Send {P} level.) Use the
Preamp Clip LED to find the Gain setting with the
maximum signal–to–noise ratio:
PREAMP CLIP LED - Illuminates when the
Gain setting is overdriving (clipping) the preamp.
The cleanest Gain setting is indicated when
Preamp Clip barely flickers at your instrument’s
peak output levels. Preamp clipping is not
harmful to your amplifier (unlike power amp
clipping) therefore reduce Gain only if you hear
unwanted distortion that is indicated by the
Preamp Clip LED.
GAIN TIP: To overdrive the first tube stage of the
preamp, connect an external preamp inline
between your instrument and the Passive input.
For the best, pure-tube overdrive sound, boost
the external preamp output, then set Gain {B} so
the Preamp Clip LED does not flash at peak
playing levels. (The Preamp Clip LED does not
monitor the first preamp tube stage to allow you
to isolate the stages in this way.)

[will33]

Should add that the aural enhancer just adds more gain on the first half of the dial, doesn't start scooping mids until about noon and beyond. Mine sounds good about 11:00.....at least 10:00. At least roll it a bit above off, gives a fuller/stronger sound.

[Crabby]

I replaced the original Groove Tubes 12AX7 in a 1997 model Red Head recently with a new JJ tube and noticed no difference even though I hoped I would.

[will33]

I was switching between a GrooveTube 12ax7 and this old Mullard I keep around here, as well as a few other oddballs but ended up at those 2, they're the most noticable difference. There's just enough difference where the bass player playing it might notice a slightly different character it their topend but it's not enough difference where anyone else would notice and some bass players might not either if they were listening to it being played mixed in with a band.


Roll the same 2 tubes in my T-MAX and it's really obvious. The Mullard having less "airy" topend and easier to put some "hair" on the sound and the GrooveTube being more "open and clear" but a little less "ballsy".



Sorry, that's the best I can do with magazine article terms.

[AdamR]

Thanks guys, I'll see what I can find local for piece of mind.

[chadds]

Tung Sol RI sounds great in my BBII. Some are noisy some are great! Rolled a lot of tubes. NOS Grey plate RCAs, Sylvanias etc. Can hear the difference. Lose preconceptions though. Electro Harmonics can sound good.

[AdamR]

TungSol is what I have been using in my Marshall guitar amps so its probably what I will pick up.

[zacwbass]

I replaced the tube in my SM400 with a JJ 12AX7. The change in sound was minor, but I found it to be slighty more midrangy and 'woody'. Good quality tube either way.