The Right Tube For The Job

[SDuff86]

Ok forgive me since I'm a newb to all this valve techy stuff but I just bought an ashton vp50 combo not the worlds best amp but I liked the sound in the shop and looks pretty rugged so for £200 I went for it. I noticed in the manual it claims to have 12ax7's in the preamp upon closer inspection it seems to have a 12at7 in the V2 position when I searched the net I noticed lots of other shops selling this amp said the same that it was 12ax7+12at7. I was just wondering why this might have been changed? Would I be able to just swap the at7 with an ax7 without biasing and would this have much of an impact on the sound quality/volumes?

any help would be great

 

[FullRangeMan]

My 2 cents are:
12AX7 has gain of 100 times, 12AT7 has gain of 60/70 times, so sound certainly will change.
Maybe it was a price choice.

 

[TonyTecson]

My 2 cents are:
12AX7 has gain of 100 times, 12AT7 has gain of 60/70 times, so sound certainly will change.
Maybe it was a price choice.

depends on the circuit used........perhaps they had no real need for more gain....

 

[SDuff86]

that's what struck me as unusual it's meant to be an amp with 4 gain channels (technically 2 channels with 2 sub channels) clean, gain, distortion and more distortion (lead I guess) but clean and crunch seems to be louder than the second 2 channels I wondered if the 12at7 could cause that imbalance of volumes?

 

[TonyTecson]

a schematic can help....

 

[SDuff86]

I had a look at a schematic myself but being a beginner/novice at this it's not much more than a great big headache to me. I know someone else who had a look that said v1,2 and 4 are 12ax7's and v3 should be a 12at7 so I switched them over and the sound quality is much better however the clean/ crunch channel still seems to get much more volume with the level set to 12 o'clock where as when I switch to the distortion/more distortion channel I'll have the level set to 3 o'clock and it's only barely keeping up volume wise I'm wondering if that's just the impact of the 12at7 or perhaps a bad tube?

 

[kevinkr]

Please post ALL musical instrument amp threads to the appropriate forum which is Instruments And Amps, Not Tubes / Valves. Please make note of the forum sub-headers which indicate where to post what. Thanks...

 

[JRGuitarGuy]

Not sure about that amp if V2 is gain hole/gain stage but 12AT7 wasn't relly designed as gain stage tube and by itself I don't think its that musical but it really shines and was designed for a driver position/PI lower Mu and waaay higher trans compared to a 12AX7 so it really pushes.

 

[Enzo]

People tend to call ALL the small tubes preamp tubes, but the phase inverter tube is part of the power amp, and thus not a preamp tube. A 12AT7 there would leave all 12AX7s in the preamp.

If you bought the amp used, someone could have substituted the 12AT7 for one of the preamp tubes. Guys do that to tame overly gainy channels sometimes.


SOmething else to watch out for: The V numbers refer to the schematic, not the tube order on the chassis. IN many amps those are the same, but on many others the tube order on the amp is not 1,2,3,4,5 straight across. For example the Peavey 6505+ has small tubes in order V6-1-2-5-3-4. But many people assume the third tube from the end will be V3. I don;t know this amp at all, but if there is some confusion or disagreement as to which socket needs what tube, that could be a factor.


And another factor. The marketing description may state all 12AX7 but the amp may ship with one 12AT7. But that doesn't neccessarily mean something changed, it could simply be a mistake or oversight in the advertising copy. In any case, in guitar amp preamps you can usually just swap 12AX7s and 12AT7s as you like. There is no bias adjustment for a preamp tube.

 

[JRGuitarGuy]

Phase inverter is still part of the preamp it serves both functions in them coupling pre and power and I don't care what amp it is if its run wide open/overdrive and depending on what is stuck in there it will overdrive and clip and add some certain layer/color/distortion to the sound, and saying its not part of the preamp and not effecting tone is pretty ignorant in my opinion lol

 

[JRGuitarGuy]

like for example go from sticking a 12AT7 in PI to putting a 12AU7 all resistor values equal and being tailored or not intended for them yet still you will hear massive difference a 12AU7 PI/driver always is MUCH quieter and sounds like you put a blanket over the amp lol, 12AT7 is not taming anything wherever you stick it that lower MU is hardly noticeable maybe slight volume drop the but the waaay higher trans IS noticeable, Like the classic GE wing-plate 12AT7 not very musical of a tube at all in my opinion less fuzz compared to any standard 12AX7 obviously but every GE I heard had less fuzz and was more clear and articulate, Its all pretty subjective from where I'm oming from I never had opportunity to test any other 12AT7s, I do have a few AY7s though and again kinda the same thing more rolled off volume, another sleeper is the 12BH7 same MU as 12AU7 but compared to any 12AU7 they sound waaay better much more dynamic still kinda buzzy though, for straight clean tone they are really superb though.

 

[JRGuitarGuy]

The 6505 would benefit with all GEs or at least a few of them, would help in the low end/clarity department and reducing fuzz/fizz would be light years ahead of the JJ ecc83s or the ruby AC5HG or whatever damn Chinese/shuguang 12AX7A or Bs that they are loaded with the JJs are bloated in the low end and dull and no character the chinese have better lows but they are fuzz/fizzy city with a hint of the old Chinese aggressive/pissed off mids. but they are NOT EVEN CLOSE to the old Chinese pill/square getter

 

[JRGuitarGuy]

any of those waay modern high gain multiple preamp tube firebreather preamps, hell sticking a 12AU7 in a slot might be beneficial in taming them a bit, 12AU7 in V1 isn't too bad depending on what one it is some are more crappy than others, I have few Sylvania black-plate square getter Au7s they are pretty nice actually in V1 as well as a few RCAs, Have few Amperex too that have very lively midrange, I like the sylvania more though has waay more detailed highs

 

[Enzo]

You jump to many conclusions, JR. I never said that the different types of tube won;t affect the sound. Of course they do. I merely claimed the phase inverter was not part of the preamp, and that might affect the manufacturer's claim that all the PREAMP tubes were one type.

If you buy a guitar preamp, it will not have a phase inverter stage, nor will it have opposing phase outputs. Likewise, if you buy a power amp, it will have a phase inverter, and will not have opposed phase inputs waiting for an inverted pair of input signals.

 

[JRGuitarGuy]

It still adds a layer of coloration or maybe not as noticeable all depends, How I hear it mostly there is a huge volume differences of course, between tube types also that factor of how close certain PI tube if both halves are even close or not, it will never be perfect between both sides obviously.