Replacing valves on a mark III blue stripe , what colour valves to replace?

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Oct 5, 2023
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Hi gents,

i recently bought a mesa mark III blue stripe simulclass 100w comes with ruby valves. i can t figuer out what valves different than mesa boogie i need to replace.i found some brands(tad) that they offer matched set depending on the colour from your original mesa valves. anybody would know how to find out?i found a little blue dot sticker where the simulclass transformer is.not sure if thats an inidication.thanks a lot guys for this amazing forum.


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On the SIMUL amps the OUTER Class A pair is biased a lot hotter. Assuming we're talking 6L6 you're always safe with RED there and in some amps YEL may fly as well. The rest are getting too hot.

If however you want EL34 in the Class A slots, GRN or maybe even GRY should be alright.

On the INNER Class A/B pair for a MKIII or IV I'd stick with GRN or GRY since they are a little colder than a MKII where I'd go YEL or GRN. Remember, 6L6 only.
Thanks very much for your reply and information gents !!i appreciate a lot
Hi, would anybody know the pc or bias point i need for the el34 and 6L6 to for the mark III if i choose a different brand?at present i have ruby el34 with pc:36 and 6L6 pc:41 .when i measure the el34 s i get 33 ma and 39 ma. my 6L6 give me 39 ma each. i am thinking about tungsol valves but not sure if i can choose same pc from tungsol.any recomendation?thanks a lot
Red - coldest
White - hottest

You will want the 6L6’s to run a bit hotter and the EL-34 to run a bit cooler from my limited experience. The limiting factor will be the EL-34’s. If you run them too hot you will have a very short valve life.
The 6L6’s as far as I can tell are typically biased cold and a warmer valve will get the bias to where it needs to be.



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