Best preamp tubes for 1966 Vibrolux

[TerryD]

Hey, I'm selling my almost perfect Vibrolux that you guys helped me resurrect and boy is that thing a monster and in great shape.

I'm selling it to an  associate professor at Eastman School of music where it might do some good.

Now I have to think a little bit "roadworthy" to give him advice.

I'm thinking tubes AND sound.

Hoffman's NOS Phillips AT7 = perfect

Hoffman's EH 6l6s in there now and seem awful good to me

I have old RCA 7025s in there now but they can't be bulletproof.  I can't believe anything could sound as good as those.  But what could I advise this guy for replacements.  Ebay NOS?  Hoffman has the Sovtek 7025s but I shudder to think about the sound in comparison to RCAs.

What's the best GZ34 replacement for endurance and sound?

NOS RCA 6L6s I'm assuming are always too much cash.  Would you agree?

Thanks for your input.

[tubenit]

Regarding your specific amp ............

In the cases when I am not buying the EH or Sovtek from Hoffman,  I like  Tung-Sol 5881 Re-Issues, Tung Sol 6V6 or JJ 6L6 or JJ 6V6 for durability.  I think the JJ's are the most durable power amp tubes I've found.

I have found quite a few different preamp tube brands that have worked well for me & have no significant preference.

I like old stock or NOS 5751's for V1 and find them durable.  No particular brand has stood out to me.  The Sovtek 5751 is a reasonable and very durable choice for LTPI and things like reverb or vibrato tubes in my experience.  I am not a fan of the Sovtek 5751 in V1 and prefer the older tubes.  I think there is a JJ 5751 and a Tung-sol 5751 being produced now?
However, I have not tried those? 

For durability, I think the Sovtek tubes in preamp are pretty reliable.  There is always a balance between durability and tone and some struggle in finding ones that consistently do both.

NO preference in brand of rectifier tubes for me.  I usually use what Hoffman sells and like his 5V4 quite a bit.

With respect, Tubenit 

[eleventeen]

I've had better luck than I can believe with EH 12AX7s. As I have boxes and boxes of older tubes around, I rarely buy tubes unless they are super cheap or thrown in with some piece of gear or a lot of stuff. The EH 12AX7s I have bought have been for repairs where I just passed on the cost, which was I think $10 on sale at G Ctr. So I do not have experience with brand new 6L6s of *any* mfr. NOS RCA's? Isn't that about a $100 proposition these days? I have had great luck with Sylvania 6L6 for many years; if there is some NOS mojo you are after, perhaps a pair of those could be found for 30% less than RCA's?


I would not be happy about throwing $300 of tubes in an amp I was about to sell!

[Toxophilite]

I haven't tried many of the newer generation of preamp tubes, I'm sure they're just  fine ii always had lots of old ones from stuff I found
As a result I've had many many of all the most coveted old ones come through my hands at one point and have tried most of them in a guitar amps preamp section
There was only a noticeable difference in the amount of amplification provided by different tubes and that was a small difference usually attributed to how strong/used that particular tube was
I would buy for reliability , that's how they always been marketed
In my experience,(mostly on the road and at shows) if tested and not too used almost all the old ones are great and I imagine the new ones are too.

[eleventeen]

The only issue with older domestic tubes is that they can often be microphonic. They are on occasion rather uneven side-to-side, as well. That would probably not matter much in a guitar preamp, but standing there at the tube tester, you get the nagging feeling that "this ain't right". Very common for older 12AX7 to be microphonic.

[Fresh_Start]

I can tell you that the first preamp tube is the most important in terms of getting vintage tone. New EH and/or Tung Sol 12AX7s set up a good baseline, then experiment with NOS tubes to hear where they really matter. I've had bad luck with new 12AT7s so you're on the right track with NOS there.

Don't want to step on Doug's toes but Mike at KCA NOS Tubes has done well for me several times. Almost NOS tubes can offer really good bargains in preamp tubes ( not rectifiers or power tubes IMHO).

Chip

[HotBluePlates]

Hey, I'm selling my almost perfect Vibrolux ... to an  associate professor at Eastman School of music ...

Prestigious music school. If your friend is a professor there, then he might have his own brand preferences for his amplifiers?

I have old RCA 7025s in there now but they can't be bulletproof. 

Few things are "bulletproof" but preamp tubes rarely fail, but rather have/develop microphonic or noise issues. If I were selling the amp, I'd put in whatever new production tube didn't have noise or microphonic issues, then let your friend decide whether they meet his needs or if he needs a different tube. Preamp tubes can noticeably influence an amp's sound, but what's best often depends on a player's taste & application (no single "right choice" for everyone).

[clyde]

I would bet that amp had wall to wall RCA's when it left the factory-great sounding tubes.  I mostly use EH and Tung Sol 12AX7's for repairs and builds.  I find the JJ's to be noisy sooner or later, not a good choice for V1.  I also find their power tubes rather inconsistent in quality, the 6V6S being an exception. As far as GZ34's, none compare to NOS.  I have used them all and find not a whole lot of difference, they all fail eventually.  The Ruby 6L6MSTR is a good-sounding reliable choice for these bottles.