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Mixing preamp tubes

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bigjazzboy

New Member
Hi all!

Quick question—is it safe or ever fruitful to mix brands of preamp tubes? My amp has two 12AX7s for its preamp section, and right now I’m sitting on a pair of JJs and a pair of Mullards, and I’m curious as to what it would sound like to have one of each plugged in, rather than just JJs or just Mullards.

Anybody do that kind of thing?

Thanks!
 
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I could be mistaken, but it might be helpful to know is the design of the amp. I have a tubed phono pre with 3 tubes (1x 12au7 and 2x 12ax7). The tubes run in different stages (V1, V2, and V3) and the L/R channel goes through each tube. As such, it made perfect sense for me to mix and match different brands and types of tubes at each stage.

But I have a VTL 2.5 preamp that uses 2x 12AT7 and 2x 12AU7 tubes. It's my understanding the the left channel passes through 1 12AU7 and 1 12AT7, ditto for the right. It would make much less sense in this scenario to mix brands of 12AT7 tubes and to mix brands of 12AU7 tubes.

Okay, I'll wait now to see if I got this right :)
 
punkzter said:
I could be mistaken, but it might be helpful to know is the design of the amp. I have a tubed phono pre with 3 tubes (1x 12au7 and 2x 12ax7). The tubes run in different stages (V1, V2, and V3) and the L/R channel goes through each tube. As such, it made perfect sense for me to mix and match different brands and types of tubes at each stage.

But I have a VTL 2.5 preamp that uses 2x 12AT7 and 2x 12AU7 tubes. It's my understanding the the left channel passes through 1 12AU7 and 1 12AT7, ditto for the right. It would make much less sense in this scenario to mix brands of 12AT7 tubes and to mix brands of 12AU7 tubes.

Okay, I'll wait now to see if I got this right :)
Click to expand...

Hm, interesting. I wish I knew more about my amp’s design. The very bare bones manual has a schematic, but I’m hopelessly lost when I look at it.
 
My hunch is that if you use a different brand of tube one channel would have a slightly different sound than the other. What is the make/model? Or can you post the schematic? Others here are probably better suited to help, but I'll take a glance at it.
 
Here’s the schematic.
 

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This article would give you a short explanation for the schematic: https://hometheaterhifi.com/volume_8_1/antique-sound-lab-15dt-tube-amp-1-2001.html

But, in short, the 12ax7 tubes are dual triodes. Each tube has two stages. The top half of your schematic is one channel, the bottom half is the other. They are using the 12ax7 tubes so that each operates solely in one channel. One section of the tube is for input, the other is treated as a driver.

Even shorter answer, I wouldn't mix up brands, although it could be an interesting way to see if you like one tube over the other. Changing brands of tubes will slightly alter the sound of the two channels.
 
punkzter said:
This article would give you a short explanation for the schematic: https://hometheaterhifi.com/volume_8_1/antique-sound-lab-15dt-tube-amp-1-2001.html

But, in short, the 12ax7 tubes are dual triodes. Each tube has two stages. The top half of your schematic is one channel, the bottom half is the other. They are using the 12ax7 tubes so that each operates solely in one channel. One section of the tube is for input, the other is treated as a driver.

Even shorter answer, I wouldn't mix up brands, although it could be an interesting way to see if you like one tube over the other. Changing brands of tubes will slightly alter the sound of the two channels.
Click to expand...

Will read up on that. Thanks a bunch for the prompt and helpful reply.
 
Something to remember about tube-rolling, if you get further into that exercise: One maker might purchase tubes from another, and re-label them, with their own brand, rather than that of the supplier. You could end up with two pairs of tubes from the same manufacturer, even though the tubes bear different brand names. You can visually inspect for differences, or post here, and ask, if in doubt.
 
bigjazzboy said:
Hi all!

Quick question—is it safe or ever fruitful to mix brands of preamp tubes? My amp has two 12AX7s for its preamp section, and right now I’m sitting on a pair of JJs and a pair of Mullards, and I’m curious as to what it would sound like to have one of each plugged in, rather than just JJs or just Mullards.

Anybody do that kind of thing?

Thanks!
Click to expand...
Technically , it should not matter if both tubes test the same, and have the same amount of gain. Although, it is my experience that there can be subtle differences that can be discerned if your equipment has the ability to resolve that.
 
I used to tube roll all the time. the 12ax7 has lots of "equivalents" and variations on the same
theme. Russian lps versions have spiral heaters, ecc83 made totally differently but to the
same electrical specs. I tried 6681s, 5751s, etc nowadays there are reissues (tungsol,
mullards, gold lions, etc) standards from JJ, China, etc.

you're going to find that, depending on the rest of your equipment and especially the
music you listen to, they all sound different.

Used these on Dynaco Pas2/3s, Conrad Johnsons, and Precision Fidelitys.

and if you find oldies like JAN, brimar, RCA, ribbed plate telefunkens (vs American
love for the smooth plates), you can sell these for small fortunes and buy lifetime
supplies of Psvanes, and others. the older Japanese ones have specialized markets.

so, my experience has me rolling tubes like eating on a regular basis
 
It's perfectly fine to do this, and I suspect if you did it blindfolded, you would not notice any differences in sound.
 
Mixing is a must imo. I have two extra strong tested Telefunken 12ax7s for the V1 and V6 pre spots. The first left and right spots in my amp. Then the next two, V2 and V7 (af amp) a matched pair of EI pre war 12ax7s. Made on Telefunken machinery but still calmed it down a tiny bit and made the vocals more airy. And then I have two telefunken 12ax7s again for the phase inverter spots, V3 and V8 .

This was the only way I could get my Bell carillon 6060 to sound perfect. With all teles I was getting this glassy sound on the vocals. Almost like when you turn the bass up too much. Liquid might be the term. I had to mix those two EIs in there and now it's literally perfect. Sure I lost a tiny bit of dynamics but sound quality went way up.

No idea why this was happening with alll teles but it was.
 
Edit that
Teles are still in the V1 and V6( left and right pre amp), but v2 and v7(af amp section) I now have 1956 Holland amperex in there. Amperex herleens from the 50s are really unbelievable tubes btw.

EI pre wars are in phase inverter now and couldn't be more happy with them. Now I woudnt do two different brands for the left and right channel in the pre. Would sound odd and most likely be unbalanced.

BTW, I'm now using eh 6ca7 and they are by far my favorite new production tube. With telefunkens in the pre amp spot they sound better than my mullard Xf2s. But with the amperex in the pre, the mullards still win. But these mixed with teles up front are unbelievable. I suggest you el34 guys try them out. They are built like tanks too and havw been a God send for my bell which biases very very hot to say the least
 
From my experience with 12AX7's the old Mullards tend to sound darker Telefunkens and Bugle Boys toward the brighter side. It's surprising how much they can affect the sound of your amp. I sell Mullards to buy the Telefunken and BB. As far 6BQ5's I've yet to find a better tube than the smokey hole Mullards. They are truly amazing.
 
Ever try a GE 7189A? NOS are almost extinct. Big sound. :)

BTW... I really like the blackplate RCA 7025. I have a bunch, that owners wanted pulled from their amps and replaced with TFK or Bugle Boys. The 7025 is a very nice sounding tube, which lasts.
 
Last edited:
Mr Boochie said:
Aren't Mullard Xf2 = EL34? Not 12AX7 or ECC83?
Click to expand...


Yes what on saying is after mixing certain combos of 12ax7 pre amp tubes I was able to get my eh 6ca7 power tubes to sound like my Mullards which was an impossibility for me for awhile. Either way they're by far the closest thing I've found to nos el34s, even thought they're not pentodes. Telefunkens are a must with these guys if you're trying to get that mullard sound. Without the teles you don't get that tight bass of the mullards. You don't get that dynamic drum crack. An amperex mixed in will work too but teles for the majority are the way to get these sounding like Mullards.

I've tried every brand pre amp tube mixed with these eh 6ca7s and while nice, and close, they're just not there without the teles. Still small differences but dam they are very extremely close and they're built like tanks. On my Bell Carillon 6060 which bias is around 60-63 mA with 385-395 plate voltage, they're the only new production that take it with ease.

I will say the Amperex in the Phase inverter is just topping on the cake. I hate using my non microphonic close to NOS 1956 and 58 amperex Herleens in my Phase but for some reason they're so dam good there. However, I think I found a combo that works perfectly while at the same time using my amperex in the af amp section. Teles in the Pre, 1 amperex on one channel in the af, one more telse on the other af section, and either EI pre wars on phase or teles in phase. Now I know I just said you don't want two different tube brands for two different channels but after my OCD non stop combo trying I came to this combo last night. As I needed just a slight addition of the amperex sound while keeping the teles dynamics which no tube can touch imo.

All great tubes and my favorites.

So what I was getting at is matching 12ax7s is key. That's how you tune your amp. And the differences are extremely noticeable. I'm the type to keep doing it over an over to I get my sound. Most will find a combo that works fast.

My favorite 12ax7s are by far Tele smooth plates. Amperex foil D getters, tilted and not, from the 50s, and the EI grey plate pre war in certain spots. Although make sure you buy super low noise phono grade ones with EI

My favorite American tube, the Raytheon ladder backplate. This tube changes sounds more than any tube I've had depending on the position its it. Fun tube. In the pre amp spots they're too dark and tubby ariund the vocals for me. But they are a great fine tune tube. In the phase they made the amp clearer than I've ever heard. Go figure. Anyway good luck guys.

And no you don't mix power tube brands
 
Since we are talking about rolling 12ax7’s, I just got a pair of Baldwin-badged Sylvania’s I really like that didn’t break the bank. Long ribbed gray plates and halo getters

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