2. amps-preamps
  3. 147225-115924

Tube Rolling for Pre-amps?

I have an Audio Research LS-16 that feeds a Madrigal Proceed HPA2 solid state amp. 

I did not choose this equipment; it was given to me. From what I can tell the original owner spent a good bit of time matching up these two components with the speakers, Aerial Acoustics 7Bs.

The tubes in the AR are original. Probably 10-15 years old? But with an extended period of not being used.

The system sounds good to me. I don't need to change anything.

However, I've been told that the tubes are old and may need to be replaced soon. I've also read a little bit about tube rolling but most of the articles I've seen talk mostly about tube rolling with amps and not pre-amps.

So I have some questions:

1) If the original owner wanted a system that sounded like a 'tube' system, why not have a tube amp and pre-amp? Does it make sense to have a tube pre but SS amp?

2) Other than outright failure, how will I know if my tubes _need_ to be replaced?

3) With a SS amp, will changing tubes in the pre-amp have a noticeable impact on SQ? In other words, is tube rolling for a pre-amp played through a SS amp a thing?

4) For someone like myself who is happy with the system and who is also easily frustrated by A/B testing is tube rolling the pre-amp even worthwhile? I can almost always hear a change when comparing various components but only rarely am able to say A is better or worse than B.

( I probably can't even articulate effectively what I look for in terms of SQ except that I like the bass to be tight, precise, well defined and not boomy. I do not like the music to be overly bright or tinny. I like depth and lushness but not overly warm. Not sure if these are things you alter with tubes.)

Thanks for any advice.


n80
lowrider57's avatar
lowrider57
5,418 posts
 
I'll add to @djohnson54 comments. I'm an avid tube roller. At one time I was addicted to rolling NOS preamp tubes when I had a SS amp. 
Depending on the design of the preamp, rolling in a different brand or style of tube can make a significant difference to the overall sonics of a system. Characteristics such as dynamics, transparency, soundstage can all be affected. Many audioholics change tubes to take the edge off the highs, or conversely to add extension and "air."  The caveat is that the amp will play a role in how much of a change in sonics you hear. Your SS amp must be revealing enough to hear the changes from the preamp. But you will hear a difference in preamp SQ or sound signature.

Preamp tubes do last a long time; thousands of hours if purchased from a reputable dealer. A dying tube can become noisy or microphonic. But IME, you can tell when a tube has reached its life expectancy when your music begins to sound dull. There may be less extension, a flat image, or less colour or drive to the music.

I'm a firm believer in having a set of spare tubes on hand. For this reason maybe you should start shopping for a replacement set.


whart's avatar
whart
3,196 posts
 
Small tubes often don't fail dramatically in the same way that amp power tubes can- but they will lose their high frequency extension and punch over time. It's almost like a new pair of sneakers- more bounce. 
I'm not sure it is worth getting carried away with expensive NOS tubes in your preamp- look at the complement- are they 6Dj8? (that was pretty common then), and there are many types and manufacturers. Obviously, you won't know what the tubes sound like til you hear them in your unit and system. I'd refresh them for sure, but am not up on current production tubes. 
rodman99999
6,206 posts
 
Tubes don’t get old/weak, from age(only use), unless they have a vacuum leak. If you’re really concerned about the remaining life of your 6922s(assuming yours isn’t the MkII), you might send them to theses guys, for testing: http://tctubes.com/tube-testing-service.aspx I’ve found them accurate, honest and reliable. Regarding your last question, YES- the presentation you’ve described, can be adjusted with the preamp tubes. Any good power amp, will faithfully pass whatever signal it’s fed, so- make it the best you can. ie: NOS Amperex(a little warmer than stock ARC tubes), NOS Mullards(a lot warmer than stock), NOS Siemens(tighter bottom, airier and more detailed/cleaner than stock). There’s no problem, trying just one pair per gain stage, at a time, to see if you like the change. I rolled tubes through a couple different ARC pres, never trying anything but E88CC/7308 (or better) iterations, with gold pins. I settled on the early Sixties, grey shield, Siemens CCa.   I’ve six in my CDP, now(glad I bought extras, way back when). Good information, here: http://www.audiotubes.com/6dj8.htm Then again- IF you’re actually happy with your sound, why fix something that isn’t broken? Just don’t go listening to a lot of live music.
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whart's avatar
whart
3,196 posts
 
Right. My point is, tube degradation with small tubes is gradual. You may not hear a nasty and don’t necessarily know that it isn’t performing as fully as it could. Testing only tells you so much. For example, I use NOS ribbed Tele 12ax7s in my Lamm SET amps. (None of these are truly ’never used’ -well, maybe once in a while at a significant surcharge over the already premium price for "pulls").  Six months ago or so, I had a sense that the amps weren’t as sparkly in the high frequencies, and nothing else in the system was amiss. I got another pair. Voila! Back to that sound I love. (The replacement pair was noisy, and the vendor swapped them out for another pair that now works fine). And that 10,000 hour figure cited for some of these high grade tubes? Sure. I’ll accept that. But those "NOS" Telefunkens on the market? How many hours have they already clocked?
( I do actually find never used vintage tubes sometimes, but it’s getting harder, and the popular ones, like the 12ax7 Tele--well, good luck. Not trying to be negative, just my reality).
I rolled bags full of 6dj8 equivalents back in the day. Literally- a few full sized shopping bags of them over the years.
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