Question on to NOS or not to NOS

[Rockin_Ron]

I got my hand's on some tubes. One is a JJ 12AX7 and the other based on my web research appears to be a NOS RCA 7025 with the halo getter and grey plates and all that good stuff!

Plugged the 7025 into V1 and the JJ into V2 replacing the stock MESA expecting to get my socks knocked off. I'm not hearing it. Am I missing something? I've read through many of the previous posts (even one that was quite informative, I think it was titled LSS and preamp tubes) showing a lot of love for these NOS tubes. Should I be hearing a dramatic difference in sound and tone?

What about these low gain versions of the 12AX7 ... the 5721? I'm looking to warm/thicken the amp sound up and take away some of it's brightness or brittle sounding top end

Suggestions always welcome.

 

[MrMarkIII]

You should test tubes one-at-a-time, otherwise, which tube is causing a change? V1, V2, both? V1 is the first tube in the chain, and thus has the largest effect. JJs have a rep as a dark-sounding tube, so try that in V1.
If you only play at bedroom volume, tube changes may be harder to hear. Too much brightness may be relieved by using the EQ controls, as they will yield more dramatic results than tube changes. The closer your ear is to the speaker, the harsher the highs.

 

[dodger916]

Not all NOS tubes are equal. The trick is to get one with plenty of strength, otherwise it could sound bland. Also, 7025s are a low-noise version of the 12AX7. I found them to lack the character I enjoy in straight 12AX7s or 5751s (lower gain version of the 12AX7).

Shopping for NOS tubes requires a lot of knowledge. I'm a novice at best. It's important to know the output for each triode, preferably in millamps. Also, as sellers using different equipment, it's important to know what the readings of individual testing machines really mean. The Hickok 539C is an excellent machine, and will give meaningful results. Other machines don't always tell the whole picture, especially with power tubes. Good sellers will also have their machines calibrated periodically.

I would also post this question in the Tubes section of the Board. There are people here with an absolute wealth of information, much so more than me.

 

[Rockin_Ron]

Not all NOS tubes are equal. The trick is to get one with plenty of strength, otherwise it could sound bland. Also, 7025s are a low-noise version of the 12AX7. I found them to lack the character I enjoy in straight 12AX7s or 5751s (lower gain version of the 12AX7).

Shopping for NOS tubes requires a lot of knowledge. I'm a novice at best. It's important to know the output for each triode, preferably in millamps. Also, as sellers using different equipment, it's important to know what the readings of individual testing machines really mean. The Hickok 539C is an excellent machine, and will give meaningful results. Other machines don't always tell the whole picture, especially with power tubes. Good sellers will also have their machines calibrated periodically.

I would also post this question in the Tubes section of the Board. There are people here with an absolute wealth of information, much so more than me.

Thanks for the reply's. Posted over on the tubes section and not getting much response. I got to believe there are some folks that have done this.

 

[ja22y]

If you're asking about pre-amp tube I'd say give NOS a try since it should last a long time and once you've found the right tube for you, it's priceless 8)
Having said that what I've found is tube makes dramatic difference in vintage design amp. I mean the more straight forward the circuit is the more audible it is. For the LSC/S the different is there but it's also being masked by 'something'. That 'something' for me is the compression and brittle brightness that tube can help but can not completely change.
The RCA 7025 to my ear is brighter and edgier than a RCA 12ax7 and I've not found a use for it yet but may be in the PI slot. I use a RCA 12ax7 in v1, it's one of the warmest US tube and it does take a little 'brittle brightness' off. To hear its characteristic, you'd need to crank the gain. The real different between tubes is when they going into saturation. Listen for the clarity and separation of the note, which is the true value of NOS tube, not just 'gain/bright/dark'.
Of course the above is N/A if you play metal.

 

[Rockin_Ron]

Hey Ja22y thanks for the info. I'll give that a try when I'm able to find some reasonably priced NOS RCA on ebay. So do you think the RCA 12AX7 is "warmer" the the RCA 5751 or the "SRV" tube. I've just read a lot of good things about it. Is all hype or truth? When you say the sweet spot is when the tube goes into saturation. What does that mean or how loud do you have to play to achieve that? I'm mostly in the 5 watt mode and play anywhere from 9 to 12 o'clock on the master. Is that enough?

BTW No metal here! Lookin for that sweet 70's Clapton type tone.

 

[ja22y]

Just to try out, you may opt for pulled instead NOS. btw most tubes on ebay are pulled anyway but they are advertised as NOS so be aware. Pulled tube can be had for no more than $15 ea
The 5751 will give you a little more clean headroom at the expense of lower overall volume. I don't like it in the LSS. I like mine clear but fat when pushed and the 5751 is a little 'thin' when matching that with the el84. It works great on my '57 Twi, however, which has 6L6 so may be it would work in a LSC. I think that the SRV tube is Sylvania 5751 and IMO the mojo is SRV himself, he can play a costco special and sounds great.
In term of sweet spot, just use your ears, since it's also depend on the gain of your pickup. I just crank it up and play with the gain/master until it sounds 'right' to me. It's roughly the point where it started to go dirty or crunchy and powerchord has 'body'.
The dirt you hear in the 5w is also coming from the power section. In this mode, I just open the master volume (max) and use the gain since this is the power breakup that can only be achieved in low wattage, w/o killing your ears and neighbor that is.

 

[BobL]

Rockin,
Please try to keep in mind that the best preamp tubes in the world are going to be of very little help if the output tubes aren't up to the task. I read all the time about people replacing one or two tubes and then claiming there is a huge and significant change in the tone of their amp. I have to say honestly that after 45 years of playing and changing tubes I find that very hard to beleive indeed.

The tone of your amp will ALWAYS be the sum of it's parts. Look at it this way. If you change one pre amp tube out of three or four any following or preceding tube in the audio chain can and will effect it's performance and tone. What good is a tube that will faithfully reproduce 20-20Khz if the tube following it can only reproduce 40-10Khz? Try selecting a good quality tube and replacing all of the pre amp tubes at the same time. If you like the sound, then try replacing the first tube, V1, with another type or style, or many types or styles, then move to V2, and on.

Finally, the output tube are the key to success. It's the output tubes that will make the biggest change in the tone of the amp as they have the final say in what comes out of the amp and every stage of the preamp before them. Personally I don't drink the JJ Koolaid. I have found good tubes for my Lonestars and JJ or Mesa isn't amoung them. And, NOS isn't a part of the mix either. My output tubes, 6L6's, are GT 6L6GE's. They have a certain airy sound that few other tubes have, and they have good solid bottom with a sweet midrange, if.....

If I use the right SET of preamplifier tubes, which are currently TungSol's. Now the exception. The lone exception is an NOSSylvania 12AX7 in V3, and only because it's the first tube I pulled out of the cabinet, and only because it cured the V3/no sound problem I ran into. Other than that tone is subjective, but please keep in mind that replacing a single tube rarely if ever cures the poor design characteristics of the tube in front of or behind it. Just some food for thought. Have fun, and good luck.