Preamp Tubes Selection (v1 Mojo?)

[Keven]

Hey guys

I've been reading up a bit on preamp tubes and see that alot of guys tend to mix and match preamp tubes in their different positions for different/better tones

i've also seen that alot tend to use some lower gain/cleaner valve for V1, like using an old JAN phillips or mullard for that position and then going with standard tubes for the remaining. also getting something different with the phase inverter too.

my amp is currently using 4 TAD 12ax7. they're good, crunch well, i think they're a bit loose in the low end and could maybe be a touch darker, or at least shift the peak frequency just a bit lower. sounds very aggressive. of course i play metal and detune alot so too dark might not be such an option, but i'm just curious. why a lower gain tube in V1? and what do you use for your phase inverter? due to my switching scheme my clean tone is a digital preamp into my 2 EL34  tube power amp. distortion is a TS-type clone with the level all the way up and drive maybe at 9-10 o clock into my amp's preamp and into the poweramp.  so the point of changing preamp valves is to improve the distorted tone.

[gwEm]

although v1 is the most important, the phase inverter tube affects the sound a hell of a lot too. it depends on the amp obviously - i've read with high gain heads its better to go with a lower gain valve in this spot. for my medium gain marshall master volume, i've found this isn't the case - it made the amp sound a bit wimpy.

[Keven]

So I could try a 5751 for the V1 and what could i use for the phase inverter? higher gain to possibly drive my power tubes harder?, i may have put my foot into my mouth saying this, this is the part of an amp i've never really bothered

mine is a sorta high gain i think. it's not a 6 12ax7 monster but the lead channel probably has 5 gain stages with a cathode follower for the second half of the third 12ax7. and the 4th 12ax7 is the PI. i need to look at the schemo to be sure. it's a 50 watter with 2 el34 as mentionned.

[Twinfan]

Personally, I only really worry about having something good in V1.

[Ratrod]

NOS 5751's (GE and JAN Phillips) are a good choise if you want to lower the gain and warm it up a bit.

If your V1 needs to handle cleans as well as high gain like in a master volume amp with a cascading pre-amp, I'd recommend the TAD 7025 highgrade.

[HTH AMPS]

try a 12AT7 in the phase inverter - less gain, but you get a deeper bass end with more clarity/less fizz.

[Transcend]

try a 12AT7 in the phase inverter - less gain, but you get a deeper bass end with more clarity/less fizz.

I also have questions regarding the PI i currently just have a set of 4 JJ 12ax7 in my tsl60.

I read on the marshall forum i should have a fully balanced valve in the PI what exactly does this mean?

I would say the only problem i really have with the TSL is that the low end can sometimes be a bit flubby a big at times

[Dmoney]

I read on the marshall forum i should have a fully balanced valve in the PI what exactly does this mean?

Balanced means each triode in the tube have operating characteristics as close as possible to each other
A marshall PI schematic is something similar to this.


each 12AX7, AT7, or whatever has two triodes in it, but they don't have identical operating characteristics.
for example the B side (pins 6,7,8) operates with lower noise (i think) and sligthly different levels of gain to side A (pins 1,2,3).

In that picture above, you can see the bottom of the triodes are all linked together to ground sharing the same resistors, but at the top there is an 82K and 100K resistor from B+. These values are setting the levels of gain differently in each triode in an attempt to make up for the operating differences of each triode of whatever tube you put in.

I think in actual fact it should be 91K and 100K, to be more balanced. A lot of people now use 100k and 100k but 82k/100k is the typical marshall arrangement.

i don't think having a balanced PI matters too much in a marshall. an imbalance in the PI can also create desirable(?) distortion in the power stage. As long its not totally imbalanced i guess. It's down to what your ears like.


certain amps have a pot to perfectly balance any tube, like the symmetry pot in the Ubershall.
I don't think balanced PI's matters when it comes to certain amps like some Orange amps, vox night train or the Peavey Valveking, which use a different type of PI (cathodyne)

[Transcend]

Thanks alot i do like how the marshall is sounding currently its just the bass is a bit loose sometimes but i believe this will be sorted once i pick up the gramma from the girlfriends mums.

as i think a lot of it is the wooden floor amplifying the bass a bit as the annoying bass frequencies are gone when i use it in other places

[hunter]

Thanks alot i do like how the marshall is sounding currently its just the bass is a bit loose sometimes but i believe this will be sorted once i pick up the gramma from the girlfriends mums.

as i think a lot of it is the wooden floor amplifying the bass a bit as the annoying bass frequencies are gone when i use it in other places

I'm pretty sure that is more related to the open back cab of the combo than the tubes. Play through a 4x12 or dial out some bass to tighten it up I suggest.

[gepetto33]

Keven,

I own a wide variety of old stock 12ax7 tubes and could tell you how each of them sound in relation to each other.  If you're wanting tighter lows, i would recommend going with a good Long Plate tube.  You have to be really careful with these, as the larger plates are more prone to microphonics, esp. in the v1-v2 early gain stages. 

Finding a quiet, sweet-sounding old stock tube is all in a matter of trusting the seller.  Notice i say Old Stock, not NOS - it's more commonly referred to as ANOS (Almost New Old Stock).  You can find perfectly good tubes, that have seen very little use, and don't command the astronomically high price of NOS.  I own a couple of Telefunkens, which are rated at 100,000 hours - they're kinda pricey, totally quiet, will last you a lifetime, plus they're easily the best sounding tubes i've come across.

There's a couple of really awesome places i could direct you to, although i'm unsure which continent you're on.  If you're interested i can refer you to some places to find these.

Otherwise, you can buy new - but they don't have many new production Long Plate tubes that meet the low noise/microphonic standard of the old stock.  The best i would recommend is the 'Preferred Stock 7025' from thetubestore.com -

http://thetubestore.com/preferred7025.html

They talk these up really good, plus i've heard great responses from people in other forums.  Perfectly good for using in V1, V2 stages.  If you're also curious about old stock tubes, hit me up and i can refer you to some good places.

[HTH AMPS]

try a 12AT7 in the phase inverter - less gain, but you get a deeper bass end with more clarity/less fizz.

I read on the marshall forum i should have a fully balanced valve in the PI what exactly does this mean?

it means that valve resellers have found a new way to fleece you of even more money and that some people have more money than sense 

in a guitar amp it makes no difference, really.  spend the extra on an old stock valve - money wisely spent.

[Transcend]

try a 12AT7 in the phase inverter - less gain, but you get a deeper bass end with more clarity/less fizz.

Im very glad that i ignored there advice and went with Bennys instead then.

Thanks

I read on the marshall forum i should have a fully balanced valve in the PI what exactly does this mean?

it means that valve resellers have found a new way to fleece you of even more money and that some people have more money than sense 

in a guitar amp it makes no difference, really.  spend the extra on an old stock valve - money wisely spent.

[jpfamps]

try a 12AT7 in the phase inverter - less gain, but you get a deeper bass end with more clarity/less fizz.

I read on the marshall forum i should have a fully balanced valve in the PI what exactly does this mean?

it means that valve resellers have found a new way to fleece you of even more money and that some people have more money than sense  

in a guitar amp it makes no difference, really.  spend the extra on an old stock valve - money wisely spent.

+1

There are two assumptions here:

1) That a balanced PI is beneficial to the performance of a guitar amp.

There is little evidence to support this assumption, although from my experiences in some designs grossly imbalanced drive to the power valves can cause some unpleasant distortion artfacts as one side of the signal (usually the anti-phase signal) is clipped before the other due to grid conduction.

On the other hand there is a cannon of thought that some imbalance in the drive to the power valves is beneficial as even order distortion isn't cancelled out. Furthermore, some manufacterers eg Mesa, Peavey have a control to vary the drive to one side of the power stage to effect variable push-pull/ single ended tones (Peavey call this the texture control). When fully on this effectively disconnects one side the PI output, ie you couldn't get more unbalanced!

2) That a balanced triode helps to achieve a balanced PI.

A "balanced" dual triode (and no-one seems to want to tell you how dual triodes are balanced, but my guess it's not under the operating conditions found in a guitar amp PI), will not help the PI to be balanced.

Sooner or later (probably later....) I will get around to adding some tech info to our web site that will go into this in more detail.

Bottom line "balanced" dual triodes for use in PIs is snake oil and a way of valve testing companies extracting more cash from their customers.

[jpfamps]

Sorry double post.....