12AX7 Preamp Tube Replacement Question

[mflemmer2]

I am planning on replacing the 4 tubes of my Peavey Rock Master preamp (currently being modded by FJA mods for a slightly lower, more vintage, open gain texture, ala modded Marshall). It currently has no-name Chinese 12AX7 tubes (probably budget variety Shuguang A's or B's). I was planning on using the Preferred Series 7025's from The Tube Store (same as the TAD 7025-S or Ruby 12AX7AC7). However, I've heard that this tube in both the V1 and V2 spots may be a bit bright (which is of course subjective). If this tube is less nasally and warmer then what I have now, no worries. Otherwise, I was considering a different tube for the V2 spot. I was thinking about a Tung Sol 12AX7 RI, but ONLY if it's warmer (less bright) than the Preferred Series. If someone familiar with these tubes could please answer specifically, I would appreciate it. If you have other suggestions for the V2 spot, feel free to enlighten me. I am certainly a tone hound, so I don't merely want the cheapest tube that does the job. On the other hand, I really don't want to spend the $$$ on NOS tubes, so I'll need to settle for good quality, new production replacements.

[Bruce / Mission Amps]

When in God's creation is... "slightly lower, more vintage, open gain texture"... !?
Tube buzz BS. Hard to wrap my head around it.

With respect to the 12AX7s.... any tube other then the generic $4.00 12AX7/ECC83 tubes, manufacturers use in over the counter amps, .... will probably be an improvement.

[mflemmer2]

When in God's creation is... "slightly lower, more vintage, open gain texture"... !?
Tube buzz BS. Hard to wrap my head around it.

With respect to the 12AX7s.... any tube other then the generic $4.00 12AX7/ECC83 tubes, manufacturers use in over the counter amps, .... will probably be an improvement.

The second part of your response is a given. As far as the first part, the Peavey Rock Master is a pretty versatile preamp, but the overdrive channels tend to have a very tight, buzz-saw kind of gain---very scooped in the midrange. I'm not really into playing nu-metal or death metal thrash stuff, so what I'm describing is a more 60's--80's kind of gain--more open, less tight. Great for 60's and 70's classic rock, but still good for Randy Rhoads, older Metallica, and Motley Crue 80's tones. Not so much Mudvayne or other such groups, but that's distortion pedals are for.

[Jazz P Bass]

You may think what you want about tube reviews, but keep this in mind.
The tubes characteristics are all over the place.
You cannot describe one tube as 'warmer, less nasily' & expect them all to be that way.
The tube itself, as an amplification element, should not 'add' anything to the circuit.
A well designed circuit should be able to accept certain tubes within a set parameter.
What this parameter is only the designer of the circuit knows.(or well thought out circuit analysis)
So, please refrain from giving adjectives to preamp tubes.
You will be much better off.

[Enzo]

You are having the thing rebuilt into something different so why not see what it sounds like with the same old tubes when you get it back, and THEN see what the thing might need to change. I never minded the Chinese 12AX7s for the most part. You may find that they sound great in the new configuration.

But if you still find you want some differnt tubes, we can hardly tell you what you will like. I would suggest getting a number of different 12AX7s, sit down with the preamp with the cover off, plug in your guitar and TRY different tubes in each socket. A tube that you really like in one socket you may hate in another socket. Each socket does a different job in the unit.

We used to have arguments about tubs in some amap like a Classic 30. And what we find is that one man describes a tube as shrill, while another describes the same tube as "well defined." And a different tube might be described by one listener as smooth and mellow, but to the other guy it sounded dull. In other words, just because I like lobster doesn't mean you will. I could tell you exactly what tube I'd like in every socket of anything I have, and after that, yoiou'd know what tubes I like, but you'd know little more about what YOU would like.

For the price of a few 12AX7s and a little time, you could find out what you think of all the tubes in all the places.

[mflemmer2]

You are having the thing rebuilt into something different so why not see what it sounds like with the same old tubes when you get it back, and THEN see what the thing might need to change. I never minded the Chinese 12AX7s for the most part. You may find that they sound great in the new configuration.

But if you still find you want some differnt tubes, we can hardly tell you what you will like. I would suggest getting a number of different 12AX7s, sit down with the preamp with the cover off, plug in your guitar and TRY different tubes in each socket. A tube that you really like in one socket you may hate in another socket. Each socket does a different job in the unit.

We used to have arguments about tubs in some amap like a Classic 30. And what we find is that one man describes a tube as shrill, while another describes the same tube as "well defined." And a different tube might be described by one listener as smooth and mellow, but to the other guy it sounded dull. In other words, just because I like lobster doesn't mean you will. I could tell you exactly what tube I'd like in every socket of anything I have, and after that, yoiou'd know what tubes I like, but you'd know little more about what YOU would like.

For the price of a few 12AX7s and a little time, you could find out what you think of all the tubes in all the places.

Enzo, I really do understand where you're coming from---of course you can't tell me what I will like. You make very valid points about "shrill" vs "well defined", etc. I AM planning on playing through the unit before changing the tubes, and if I absolutely love it, I probably won't change the tubes after all. BUT---I'm probably just wondering if the grass is greener. I recently changed the power tubes in my Peavey Heritage VTX (usually driven by the Rock Master) from the stock Sovtek 6L6's to TAD 6L6WGC-STR's, and really LOVE the difference they make! I thought if I described the overall sound I like (classic rock/blues tones, usually Gibson), someone would have an idea of my tastes. Although you make a lot of sense, let's face it, not everything is completely subjective. Not many people would say that Roseanne Barr is better looking than Scarlett Johansson, or that one of the cheap guitars that Esteban sells on infommercials sounds better than a Martin. Granted, those are starker contrasts, but I basically want to know if the tubes I mentioned are more bassy or trebly in comparison with each other. I do appreciate your thoughtful response.

[Chuck H]

pffft!!!

[Steve A.]

To expand on what Enzo suggested you ought to put together an assortment of preamp tubes- if you are committed to tube amps it is a good investment. Tubes change from year to year and even from batch to batch so we could be comparing apples and oranges. One tube that I like a lot for smoothing out a harsh OD channel is the GT5751M, which is their Mullard copy made in China. Reportedly it is like a weaker version of their discontinued 12AX7M, which itself has only about 70% of the gain of a typical 12AX7 which would bring it down to maybe 40%. However I like how the tube sounds in my amps- to me it sounds a lot like some old used stock 5 Star 5751's from the 50's and 60's.

I was going to order a few of those TAD 7025's to check them out,. I read somewhere that they are like 9th generation Shuguang 12AX7's.

BTW while NOS 12AX7's can be pricey the lower gain 12AY7's and 12AU7's are usually more reasonable. Or look into Used Old Stock 12AX7's...

Steve Ahola

[Steve Conner]

Why not ask FJA what tubes he would recommend to go with his mods?

I have "Used Old Stock" Mullard, Mazda and Philips preamp tubes in most of my tube gear. They were very reasonably priced, if not downright looted from old lab equipment. But they're not guaranteed to sound at their best in a modern design that was made with the Chinese tubes in mind.

Not everything is subjective, but few things are more subjective than guitar tone.

[mflemmer2]

Why not ask FJA what tubes he would recommend to go with his mods?

I have "Used Old Stock" Mullard, Mazda and Philips preamp tubes in most of my tube gear. They were very reasonably priced, if not downright looted from old lab equipment. But they're not guaranteed to sound at their best in a modern design that was made with the Chinese tubes in mind.

Not everything is subjective, but few things are more subjective than guitar tone.

Thank you Steve A. and Steve Conner for the good feedback. I have asked Jerry at FJA, but he's really hard to get ahold of. I'm sure if he responded, he'd suggest that I wait until I hear the preamp with the current tubes before making changes, which is what I plan to do at this point. I guess it won't break the bank to get several other tubes and do some experimenting. I appreciate the responses.

[Steve A.]

I have "Used Old Stock" Mullard, Mazda and Philips preamp tubes in most of my tube gear. They were very reasonably priced, if not downright looted from old lab equipment.

When I was an HVAC service tech there was a church in Lafayette with an old heating system from the 50's that no longer worked properly. I crawled up into the attic and found that the Barber Coleman controls were run by a 12AX7- Telefunken! I came back with some Sovtek or Chinese pullout and replaced the tube, rushing home to try out my newly found treasure. Damn- it sounded like absolute crap with hardly any gain at all. On the bright side the church called back and said that their heater was working perfectly- I guess those crappy tubes that the big mfgs put in their cheap amps work okay in some applications.

When Bush the Younger sent out the $300 tax rebates in 2001(?) I spent it ALL on used old stock tubes from a seller I found on-line. No Bugle Boys but I got a lot of old Mullards and Telefunkens. The reputable used tube sellers do run some basic tests on their tubes and might even write down the gain figures on the box. And they usually offer a 30 day guarantee, offering to exchange them for something else if they don't actually return your money.

Steve Ahola

[Steve Conner]

I have two Telefunken 12AX7s that I got from a scrapped Grass Polygraph. Same story unfortunately, they seem pretty worn out

On the other hand, I was scrapping a tube regulated power supply that had only seen light use, and found a bunch of Mazda 6L13s in it. Turns out it is just an alternate part number for the 12AX7, and they were all in good condition and sounding great!