Express 50/5w pre amp tubes

[donnyb]

Hi to All,
Been reading posts on my subject topic for a few weeks now, just seeing what what other Express 50/5w owners have found through experimentation. I have had good experiences using Dougs Tubes tone kit for my amp, but had read on this forum that there may be a question over which tubes Doug actually intended to go into V2 (1st stage gain) and V4 (PI), due to other Mesa amps using V1 for Ist stage (as one would expect) and V4 for reverb.

Be that as it may or may not be, I have read heaps of different forums including this Boogie Board Forum, and am now looking at 6 new tubes in their little boxes purchased from different suppliers, based on recurring comments from different user's experiences.

Below I list what I have here, and where I think I will put them in brackets. Would appreciate your views, before I do the deed.

(V1) electro harmonix 12AX7........ OR JJ ECC83S (2nd stage gain)
(V2) Tung-Sol 12AX7 (1st stage gain)
(V3) Mullard 12AX7 (3rd stage gain)
(V4) Sovtek 12AX7LPS Matched and Balanced (PI )
(V5) Sovtek 12AX7LPS (reverb)

Note that I have 6 tubes for 5 positions, so there's room for different combinations in different positions.

Again, appreciate any comments on these tubes and the proposed positions, before surgery.

Cheers !

 

[EtherealWidow]

I have a 5:25, but here's what I use for recording.

V1: Tung Sol 12AX7
V2: EH 12AY7
V3: EH 12AY7
V4: Tung Sol 12AX7
V5: Nothing
Power tubes: Sovtek EL84

Makes the Burn channel more useable in terms of gain and takes away some of the nasty compression that the Express does with all AX7's.

 

[donnyb]

Thanks for that Ethereal W. Quite a mix you have there. What happens electronically in the amp when an AY7 is used over an AX7 ?

Also, can you also elaborate on the express sounding compressed?

Do you mean what I had noticed when I bought mine, ie that the Clean Channel sounds great in clean mode, a lot of depth and sparkle together, but the burn mode sounds a bit synthetic with bassier solo notes crumbling away (ie on the E and A strings up to the say, the 10 fret), and the treble notes "thin and grating" ?

Any views on the mix of tubes I have bought?

Cheers,

Don

 

[donnyb]

In the absence of any further posts, I did another afternoon of experimentation with tube swapping.

It is amazing how swapping just one tube with another in a certain position can make such a difference. Case in point, I swapped out the newly purchased Mullard 12AX7 in V3 (third stage gain), for a Penta 12AX7 previously run in that position for 9 months, using the new mix of valves I purchased (as detailed in my first post) in the other positions I anticipated.

The result was a drop in presence, showing up most noticeably in the clean channel. I could use the term 'flat' too.

Anyway, for those that like to experiment, I have settled on the following placements (for now), which I notice has given the cleans a nicer timbre and the dirty a tighter attack on the 6th and 5th strings, but maybe a little too bright on the 1st string. However, I am using a Burstbucker #3 on the bridge....

V1: Electro Harmonix 12AX7
V2: Tungsol 12AX7
V3: JJ EC83S (or the Mullard 12AX7) both were similiar.
V4: Sovtek 12AX7 LPS Matched and Balanced
V5: Sovtek 12AX& LPS

Still have a bit of white noise on the dirty channel at idle, but not annoying.

Also, I am not really into reverb, so have not played around with V5. The tone kit I had in there used this valve as well, so it has just got a new replacement of this same valve now. Anyone found something better for this position?

Cheers,

Don

 

[EtherealWidow]

Hey! Sorry for the delay in response. A lower gain tube like a 12AU7 or 12AY7 does simply what it sounds like. It reduces the gain of that particular stage. Sounds simple but the effects are drastic because by reducing the gain you're not only changing the amount of signal that's going through the amp, but also the harmonic structure and frequency response of that stage and all the stages afterwards. What it does practically speaking in an Express amp is it makes the sound a lot more natural. I mainly play with higher gain settings, which just sound really squished to me with all 12AX7's. Kind of hard to explain, but if you've ever played a high gain amp with a compressor with the compression turned up all the way, it's kind of like that. With less gain, the sound is less compressed, and I'm able to hear a lot more detail in chords that have 4 or more notes at high gain settings. I don't have much of an opinion on the tube cocktail you're using. Haven't had much of an opportunity for tube rolling, but I've heard good reviews on the Doug's tube cocktail.

Also, even though I use lower gain tubes to get rid of all that squish from the amp, I still use a compressor pedal with a fair amount of compression. Let's me adjust the "distortion/compression ratio" I guess. All I know is, I like the tone I have.

 

[Krek13]

Hey! Sorry for the delay in response. A lower gain tube like a 12AU7 or 12AY7 does simply what it sounds like. It reduces the gain of that particular stage. Sounds simple but the effects are drastic because by reducing the gain you're not only changing the amount of signal that's going through the amp, but also the harmonic structure and frequency response of that stage and all the stages afterwards. What it does practically speaking in an Express amp is it makes the sound a lot more natural. I mainly play with higher gain settings, which just sound really squished to me with all 12AX7's. Kind of hard to explain, but if you've ever played a high gain amp with a compressor with the compression turned up all the way, it's kind of like that. With less gain, the sound is less compressed, and I'm able to hear a lot more detail in chords that have 4 or more notes at high gain settings. I don't have much of an opinion on the tube cocktail you're using. Haven't had much of an opportunity for tube rolling, but I've heard good reviews on the Doug's tube cocktail.

Also, even though I use lower gain tubes to get rid of all that squish from the amp, I still use a compressor pedal with a fair amount of compression. Let's me adjust the "distortion/compression ratio" I guess. All I know is, I like the tone I have.

you forgot to mention the most important effect - VOLUME LOSS!!

 

[donnyb]

Hi Krek,

That affect may be a good thing with this amp. A common comment I have read from Express 50/5 watt owners, including myself (!), is how loud this amp is, even in 5 watt mode. Plenty of head room, yes, but in the stratosphere regions I reckon.

I play usually in large semi open air situations, eg large basketball court size buildings with a high roof and mostly open sides, or in typical 400 seat concert halls.

Before I purchased an Alex's Attenuator, I mainly used the 5 watt setting (mic'd up to PA front of house), and thats for rock music !! With the attenuator, I can finally use the 50watt mode, but even then I cant crank the master volume past 10'o clock, with the attenuator on its -9db (second lowest) setting.

My gains are set around 9.30-11'oclock on the Clean Channel (depending on song genre), and noon to 3'oclock on the Dirty Channel for solos.

So I am thinking it may actually be a good thing to have pre amp tubes that would allow me to be able to drive the main output tubes more that the 9-10'o clock position I need to have it at currently, and get those output tubes clippin' !

What do you think?

 

[EtherealWidow]

I mentioned the volume loss. That's the smaller amount of signal going through the amp. The reduction in volume works well for me, although it doesn't necessarily mean earlier breakup, cause the power tubes distort with a certain amount of current going through them. The difference now is that you have to turn the master higher to get that same amount of current.

 

[MrMarkIII]

You cannot "drive" the power tubes at low volumes.
Not going to happen, unless you use an attenuator.
If you are lowering the gain in the pre-amp by using pre-amp tubes with lower gain factors, thinking you can push the power section now because you have to turn the master up, what's happening is now you have to turn the master higher to achieve the same amount of overdrive you got before at a lower setting of the master knob when you were using 12AX7s.
To overdrive the power tubes, you need to turn the master volume UP, usually above 5. Without an attenuator hooked up between the amp's *output* and *speaker* (and anything else is NOT an attenuator), you will. be. loud. The attenuator acts as a post-power-section master volume.
Anything else is just reducing the signal going to the power section, which ain't making things dirtier, quite the opposite.
Not that there's anything wrong with that.
It still could be a sound that works in your situation.

 

[donnyb]

OK, thanks Mr Mark111. Thanks for the technical insight there.

As I said, I do have an Attenuator (Alex's), and it has let me into the 50 watt mode now, with good effect, albeit still a bit loud on stage (for the rest of the Band that is !!!).

When you say in your post "To overdrive the power tubes, you need to turn the master volume UP, usually above 5"....do you mean the 5 o'clock position on the MV knob ie., so nearly full volume...... , or an imaginary 5 out of a possible 10 on the MV knob , ie half way on the MV knob?

Regards and thanks again.

 

[MrMarkIII]

Just a ballpark example, not anything exact.
The point is, if you want to get power tube overdrive/distortion, you need to crank the master. The only way to do this and be quiet is to use an attenuator.

 

[Krek13]

Hey donnyb,
I didn't say that the volume loss is a bad thing, I just wanted to point out that it's there if you use lower gain tubes...
and I totally agree with MrMarkIII, you just can't drive the power tubes more by using lower gain tubes in the preamp, that's a fact

 

[donnyb]

Thanks Krek. Its a case of what seems somewhat logical is just not . The electron world is a mystery to us more mechanical types, something psych tests confirm.

Here's an example of skewed thinking on my part : Imagine a singer in front of a live microphone. The singer represents the pre-amp. The PA amp which happens to be a valve type represents the output tubes.

The singer (the pre amp) is delivering a desirable tone out of his mouth.

But the singer moves too close to the microphone so the volume though the PA shoots up. The PA operator turns down the volume of the PA ( the output tubes) to compensate. No big deal to tone delivered.

Conversely, the singer moves way back from the microphone, so the PA is turned up, but turned up so loud to compensate that it starts to distort and even feedback. A big deal to the tone delivered, in this case not in a nice way.

In both cases, the voice tone leaving the singer's mouth is the same, but in the second case, where the PA is turned up, some nasty distortion is added to the sound heard by the audience.

This is how a mechanical mind can be led into thinking that sending a nice pre amp tone at a lower volume/signal to the output tubes, should result in the output tubes needing to be turned up into nice distortion and nice feedback territory.

2+2= 5.

Live and learn

 

[Krek13]

don't worry man, it seemed logical to me few years ago too so no big deal here, tried it and it doesn't work, later I had some tech guys on my local forum explain it nicely

it's like putting a volume pedal in the effects loop, you can lower the volume but you cant use it to drive the power tubes

 

[EtherealWidow]

Well that's a little bit of a tough analogy, because even the PA system has a preamp that the mic goes into, and then gets amplified by the PA's power amp. The singer in the analogy would be more of the guitar in our situation. He's the instrument.

The most common way to distort a tube is by sending a large signal into it.

The basic anatomy of an amp is as follows

Preamp (often times consisting of multiple stages feeding into each other)
Effects loop (optional, of course)
Power tube/tubes
Output transformer
Speaker

The thing is, when you distort the preamp of an amp, you don't have to turn the master volume up. The signal distorts early on before it hits the master volume.

The master volume controls how much signal goes to the power tubes. Most people would agree that power tube distortion sounds better than preamp distortion. The problem is, in order to send a large enough signal into the tube to distort the power tube, you're also sending a larger signal into the speaker, which is louder.

You can view an attenuator as an extra volume control that goes between the output transformer and the speaker. It allows you to turn the master volume up, getting more signal into the power tubes and distorting them, and then turn the volume down on the attenuator right before it hits the speaker.

The reason that lower gain preamp tubes don't allow you to distort the power amp more is because when you insert a lower gain tube, it reduces the amount of signal that is produced by that stage and the amount of signal going into EVERYTHING after it, including other preamp tubes, whatever you have in your effects loop, power tubes, output transformer, attenuator, and speaker.

That's why you have to turn the master volume up more just to get that same amount of signal going into the power tubes.