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Replacement pre amp tube for Ashdown ABM 300 evo II


Dudgeman
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I know nothing about Tubes (apart from the geezer on Soccer AM..;-) ) apart from the fact mine isn't working properly so I need a replacement.
Can you give me some advice. Looking for a solid reliable tube...I hate Chinese made stuff but if that is my only option then so be it. Don't mind a bit of growl...just have no idea where to start.

Any help gratefully received


ta.

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[quote name='Dudgeman' timestamp='1327540591' post='1513243']
I have done a touch of research and thought that was the one. Is it best to replace like for like or is there a better alternative?
[/quote]

The 12AX7 is rated at 100%, and there are various alternative ratings that give lower gain so stay cleaner longer, but they may also reduce output (admittedly that's less of an issue given the way the ABM is designed): there's a good explanation of this [url="http://thetubestore.com/gainfactor.html"]here[/url].

Likewise, the "Valve Drive" function in detailed the ABM manual. If you haven't seen it, it says:

[left][color=#0000cd][size=3][font="GillSans"][font="GillSans"]This routes the signal either through a clean Solid State amplification section (control on zero) or through [/font][/font][font="GillSans"][font="GillSans"]a Dual Triode Tube amplification/overdrive section to add either tonal character, i.e. warmth with the [/font][/font][font="GillSans"][font="GillSans"]control set at 9 o’clock, a slight edge in the sound at 12 o’clock, through to an increasing degree of Tube [/font][/font][font="GillSans"][font="GillSans"]distortion/overdrive as the control is advanced to maximum.A Mix of these two amplification sections can [/font][/font][font="GillSans"][font="GillSans"]be achieved with this control. N.B.The degree of Tube distortion with this control will also depend on the [/font][/font][font="GillSans"][font="GillSans"]setting of the INPUT control.[/font][/font][/size][/color][/left]

So, whether to change the valve gain rating depends on whether you want to change the character of the tone you get with it. Given the fact that you can blend the amount of valve you get from just a hint of warmth to some decent overdrive, if it were me I'd just go for another quality 12AX7, and as Pentode says, there are loads to choose from! You may find you change the tone by using different brands of 12AX7 alone...

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Top advice...thanks. So stick with the 12AX7.....so whats the difference between all the brands..Is it a "get what you pay for" scenario here or will they all sound different. I am not precious about this as I am now using Marshall gear but the Ashdown is a back up and it could be interesting to learn more in case the Tubes go in the Marshalls.

Thanks again

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[quote name='Dudgeman' timestamp='1327580309' post='1513599']
so whats the difference between all the brands..Is it a "get what you pay for" scenario here or will they all sound different.[/quote]

A lot of folks say that different makes have different tonal characteristics. When I changed the JJs out of my LB for Mullards, for example, the tone warmed up a lot and was much more musical.

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