Looking for opinions about a JAN-Philllips 5751 as a driver.

[EtherealWidow]

I'm looking for something dynamic, but I think there might be a much better option in terms of a tube in the P.I. slot. http://thetubestore.com/sylvania5751.html

 

[212Mavguy]

Best way is to just do it. See if you can get one with balanced triodes. Not a huge expense.

 

[EtherealWidow]

Nah see I'd like to get something else. Just reading the description of it and contemplating a fair amount more, I feel there are better options as a phase inverter, I just don't know what. Maybe a Sovtek 5751. And I'm not so sure I believe in the balanced triodes mumbo jumbo although there's a fair amount of debate on both sides.

 

[94Tremoverb]

Just try it. The worst that will happen is that you might not like it or notice much difference, and then you have a decent spare tube you can try in other locations. The 5751 is just a little lower gain and clearer than a 12AX7, it won't make a huge difference in the PI - some, but not as much as it will in a gain stage.

I like a 12AT7 in the PI in every Mesa amp I've owned and tried it in - it's cleaner and clearer than the stock 12AX7. I only use old-production tubes - the JAN/Philips 12AT7 is a great tube, still easily available and not expensive. Personally I wouldn't even consider putting a Sovtek preamp tube in anything I cared about the tone of .

I don't believe in the matched-triode thing either, since the phase inverter *circuit* is inherently unmatched.

 

[2CDR]

out of all the tubes(NOS and currant production) that i own and have tried in the PI of my 2 channel dual the sovtek LPS is the one tube that i keep coming back too.

 

[evilpresence]

I'm still slowing playing with different tubes and am new to the tube swapping but I did put an RCA 12AT7 "EZ" Code (I have searched and haven't found much of anything on that code) in my PI slot on a DC-5 and I did not like the way it dropped the gain. I put a JJ 12AX7 back in my PI and tried the RCA 12AT7 in the V2, V3, V4, and V5 slot. I believe it sounded the best in the V5 slot.

I haven't tried the RCA 5751 in the PI slot. I'll try it tonight or tomorrow and report back my findings.

Before I did research, I went with the guy at Guitar Center's advice and put in six JJ 12AX7s. I can tell you adding the Mullard and RCA 5751 made monster tone changes for the better.

current setup

V1: Mullard 12AX7 Blackburn 1961 NOS
V2: JJ 12AX7
V3: JJ 12AX7
V4: RCA 5751 Black Plate, Triple Mica 1959 NOS
V5: RCA 12AT7 EZ Code
V6: JJ 12AX7


Hopefully I didn't go offtopic too much.

 

[EtherealWidow]

Really? I was thinking of the LPS as a PI, but then I convinced myself that if I'm going to buy one I should use it in a gain stage. I don't know. Here's my current tube wishlist for my Express.

V1 - Tung Sol 12AX7 R.I. (Second and third gain stage)
V2 - Preferred Series 7025 (Input tube, first gain stage)
V3 - Svetlana 12AX7 (Fourth gain stage, FX Return)
V4 - Undecided (P.I./Driver)
V5 - Svetlana 12AX7 (Reverb)

In reality, the reverb tube is still up for debate. Maybe I'll use the JAN-Phillips for the verb and another preferred series for the PI.

And has anyone here heard of the Preferred Series tubes? Can't find them on any other website. I know they're Mullard reissues, but I can't seem to find who's the manufacture of these.

http://thetubestore.com/preferred7025.html

Ah and if anyone cares I'm also going to use some Preferred Series EL84's. Hear they sound superb.

 

[EtherealWidow]

Nah, Evil Presence, you didn't go off topic. Always good to listen to the knowledge of a tube roller. Never changed the tubes out of my amp and I'm getting ready to record so I'm trying to find a good tube cocktail, rather than going with the one from Doug's tubes. I just don't like the idea of "Yeah, these tubes in this order work on pretty much all Mesas." By the way even though I'm not too keen on the "Just buy it" method that two of you advised, I probably will anyway because I was thinking about buying one as a mic preamp tube anyway. Then again, if the Preferred Series really are as magical as The Tube Store makes them sound I might just put one in every slot of everything I own.

 

[94Tremoverb]

The 12AT7 will sound good in V5 of a DC-5 because that's the reverb tube (both drive and recovery). It won't change the actual tone of the amp itself but having deeper and clearer reverb will take away some of the muddiness you get from it and make the amp *seem* like it sounds better. I always run 12AT7s for reverb too... it's a trick I got from Mr. Fender .

The one thing to be really careful of with 12AT7s (and 12AY7s, if you're tempted to try those too) is that you must *not* try one in a cathode-follower location, such as V3 and V4 in a Dual Rectifier - the cathode-to-filament voltage rating is too low, 90V as opposed to 250V for a 12AX7, in a circuit with about 200V on the cathode, and the tube will likely blow or at best sound bad. Some Russian-made 12AX7s also have this problem due to being poorly spec'ed - not all, and not even all of any type, but enough that it's definitely a generic problem.

You can't go by the "type X in V1, type Y in V2" sort of rule, because even among Mesa amps they do different things. Some have radically different set-ups, with some real oddities like the Maverick having V1 as a cathode follower and the Tremoverb using half of V1 for the reverb recovery.

 

[EtherealWidow]

Yeah I was going to use a 12AT7 in the reverb position but I wasn't totally sure just because they had different plate voltages, so I was going to go with a tube that had 12AX7 plate voltage, but was lower gain. Maybe I'll just look into an AT7. And I saw your post on Tung Sols not being any good in cathode follower positions so I called up Marcus Daniel from Mesa and asked him if the Express had any cathode followers and he said that it didn't. And just to add to the "differing designs of Mesa", the Express is weird in that the V2 tube is the first gain stage.

 

[212Mavguy]

@94 tremoverb...

Yes, that PI circuit may very well be unbalanced, but which side is going to automatically be stronger? At least when using a balanced PI tube that circuit imbalance you accurately speak of will be preserved if it is deliberately designed in.

My Fender 160 PS uses a 6v6 as the PI position into a power tube driver transformer, unusual schematic to say the least, you can bet that circuit's balanced! The clean sustain is wonderful in that amp. And for giggles I just might stick in a vintage 40's coke bottle shaped 6f6g, 6v6g, or...Ken Rad 6l6G... or 50's Tung Sol 5881 in that PI slot to see if it sounds good or just makes all the tones go to mush...I have some preconcieved ideas how things will go for each tube type but will let my ears decide. Have certainly been surprised before!

@ ethereal widow and others here:

As far as the Sovtek 5751 or 12ax7 compared to the older, out of production stuff they are bottom of the barrel, especially in terms of tube life. With that said, if you like that tube's tone, that's fine, I won't make ridicule for that, that's unfair. Just don't expect it to live as long as that JAN Sylvania or have the syl's tonal girth, the Sovtek will probably sound a bit shrill on top and lacking lower mids and bottom end in comparison. If the JAN tube is a good one (which is far more likely statistically than any Sovtek 12ax7 or 5751) it will last much longer in that hardest working preamp tube in the whole amp, the phase inverter...The vintage GE green print 5751 is a great bang for the buck tube easily found on ebay.

Finally, the reason that I said "just do it" is that you really don't want to get your tube knowledge from gossip, you gotta roooooooll another one... just like the other one... You don't need to go totally OCD like I have :wink: but there IS a reason 94tremoverb said what he did about using only old production tubes in his amps, we agree on that completely, it's for reliability and that thang called tone. And if you must have new production stuff, then by all means get a quiver of different types, you will be the better for it because your ears will tell you what you need to know, and finally, do not expect the tones you prefer right now to be the same as a couple of years down the road. For that reason alone it's good to stock up, whether new production or vintage.

After collecting about 300 + vintage 12ax7's, 12at7's and having real Tung Sol 5751's as well as 5751's by GE, Raytheon, and JAN Sylvania, my ears listening again and again do tell me more than what my eyes read what tube store salesman of only modern production or the most common vintage stuff are writing about. I stand by my original post gladly.

Peace.

 

[EtherealWidow]

Hmmm. Good points there Mav. That Fender sounds really weird, in an "I'm totally jealous" kind of way. Maybe a balanced PI is a good idea. Besides, a couple extra bucks for one tube won't be so bad. I think I'm going to go with a JAN-Philips 12AT7. While we're at it, anyone got any opinions on the Preferred Series from Tube Store?

 

[94Tremoverb]

It's possibly true that a balanced PI tube maintains the same circuit imbalance (provided the tubes are close to identical in other ways too), but it's definitely not true that the PI circuit imbalance is intentional! And I'm pretty sure that changing the tube type, brand or even the exact gain of a particular tube will have much more of an effect than whether the tube is balanced or not.

Here's why...

The first side of the typical Long-Tailed Pair PI (used in most guitar amps including all Mesas as far as I know) is a standard gain stage with the input at the grid, which produces its output at the plate but also modulates the cathode voltage because the cathode resistance is much higher than for a normal single gain stage (this is the 'Long Tail' bit). This varying cathode voltage is then used to drive the other side, which has its grid (effectively, via a cap) grounded, and then its output is also taken from the plate. So... the signal in Side 2 has already been modified by Side 1, including any distortion, and if the first side is clipping then the second side cannot track the input voltage at all on the peaks. Side 2 also has lower gain than Side 1 because it's being driven by the reduced signal level from Side 1's cathode (effectively a cathode follower with significantly less than unity gain) - so to fix this, the plate resistor values are offset to reduce the gain in Side 1, usually 82K vs. 100K for Side 2... but this is not an exact match (even if the resistors were 1% tolerance or better, and in older amps they can be as much as 10% even before they drift off with age), it's just the two standard values that give something close to the right result. Some amps have used 91K vs. 100K, and some don't even bother with different values at all. It's all a bit crude, in other words.

Then, in most amps there is negative feedback from the power stage applied to the bottom of the Long-Tailed Pair... which means that if the power stage clips, the signal in the phase inverter is then unbalanced even more because Side 2 is much more affected by this than Side 1 which is still being directly driven by the input signal. This is why, when you crank up an old Marshall or something similar and look at the power tubes, the one nearest the PI tube is always visibly more stressed than the other one. The balance is not even remotely symmetrical and varies according to signal strength. This type of complexity is of course one reason a cranked up tube power stage sounds so interesting and touch-responsive... but it also means that any notion of balancing the PI tube is irrelevant - the two sides are really operating entirely differently.

I think you can hear as much difference between different balanced tubes as between any other randomly selected tubes. To really lock in any particular characteristics, the tubes would need to be matched to *each other*, as well as the two triodes within each one being matched... exactly as you can't say that one matched pair of power tubes will perform the same as another matched pair, because the two *pairs* may not be the same - a cold-running matched pair won't preserve the same sound as a hot-running matched pair.


After all that I'm off on holiday for a week .

 

[212Mavguy]

Trem! Enjoy your vacation! Nice post! Am aware about the long tailed pair thang and how it works, but you did describe it elegantly. Yep, the bias on the output tube pair setting causes a difference from set to set depending on bias setting for each pair. Mesa amps are legendary for having a cold bias in their output sections, but not all of them are that way! Some are biased relatively hot, like the Maverick, for instance.

The lack of balance for the tube in the PI tube slot could be either way, the first triode could be stronger than the second, or vice versa. One way could provide a more balanced signal going to the power tubes, the other could provide more imbalance. Again, that circuit was designed to have specific values for both sides. So yes, having a balanced PI complements an "imperfectly balanced" circuit that was actually designed to have some semblance of balance. There is some inconsistency in the parts value of tube gear, that is why resistors are graded to be within a certain percentage of each other. Three of my amps are boutique designs that have adjustable bias as well as adjustable bias between the pair of power tubes. You can really dial them in and their basic tone set varies a lot depending on where those bias settings are, especially the MarshallJTM 45 type (done up better) by Siegmund, his Midnight Blues series. Those not only have adjustable bias and bias balance adjustment for the power tubes, there is a bias adjustment knob fir the first preamp tube! There is a tone-al reason why that amp was awarded amp of the year by Guitar Player magazine back in 2005. If you are wanting to really dial in your amp, some time reading about vacuum tube theory as well has having someone with the tech skills and experience like fellow board members Stokes, 94tremoverb, or Monsta-tone put in the adjustable bias mod in your Mesa amp (once it's out of warranty :wink: ) will remove the handcuffs that a non-adjustable bias places on Mesa amp users, and in most cases those "handcuffs" actually are helpful to the vast majority of guitar amp users who know only enough to be dangerous to themselves or their expensive, complicated amps!

Or going back to my admittedly mad scientist philosophy of don't take what others write about for granted, including myself, roll the tubes and see what your ears like the best. If you do some searching you will find here some posts by Timbre Wolf detailing the tones provided by various out of production 12ax7 and 12at7 types as well as discussions with various board members, they are really helpful for the ones who are more curious.

 

[EtherealWidow]

Well... this is all just an overload of information. Clearly I've still got some thinking to do. I've been wondering though, what would putting a 12AT7 tube in a 12AX7 socket do? I know that the AT only has 60% of the gain of the AX, but it's mainly the plate voltage I'm concerned about. How would that affect things? And would the bias mod really void the warranty? I've had mine for less than a year but I've been thinking about getting the bias mod done from the little shop that I got the amp from. I was told that if the mod is performed by a qualified tech that it wouldn't affect the warranty. Same thing with converting a parallel effects loop to a serial effects loop.

 

[212Mavguy]

Sorry about that! I'd make sure from Mesa on the warranty thang. Haven't done any modding to my Mav yet, but it's long out of warranty. About the at7 in place of the ax7, I prefer to put the at7 in so it is before the ax7 in the amp... you will need to turn the gain up more to get the same amount of volume or in the case of overdriven settings, to get more dirt in your tone. Even though my Siegmund is designed to run 12ax7's, I run a Raytheon military stock 12at7 black plate in V1, and follow that with a Tesla e83cc (10,000 hour rated Euro 12ax7 type) in V2. Chris' fave setup in that amp is a vintage Tung Sol 5751 in both V1 and V2. The very first JTM45's used 5881's for the power tubes, not el34 or kt66! I have a very tightly matched pair of vintage Tung Sol 5881's to run in that amp when I want, and it sounds really nice with them. But currently I am running vintage British kt66's in it.

 

[evilpresence]

I tried out the 5751 in the PI slot. Once again, for me, just as my 12AT7 did, the 5751 took away too much gain to leave it in the slot. The gain would break extremely late and it just not for me. I do have a NOS Mullard 12AT7 flying in from Germany... soon. I'll put that in the PI slot to see how things go.

This was the cocktail that I did not like.

V1: Mullard 12AX7 Blackburn 1961 NOS
V2: JJ 12AX7
V3: JJ 12AX7
V4: JJ 12AX7
V5: RCA 12AT7 EZ Code
V6: RCA 5751 Black Plate, Triple Mica 1959 NOS


This is the cocktail I am currently using.

V1: Mullard 12AX7 Blackburn 1961 NOS
V2: JJ 12AX7
V3: JJ 12AX7
V4: RCA 5751 Black Plate, Triple Mica 1959 NOS
V5: RCA 12AT7 EZ Code
V6: Mesa Boogie SPAX7