Power tubes in Express 5:25

[Digirat]

Hi

Apologies if this is a really dumb question ( ) but......

The Express 5:25 runs 2 x EL84 power tubes. I thought that MESA recommends always using matched-pair power tubes, but as far as I can see on their website, the EL84 isn't available in matched pairs.

Is there a reason why the 5:25 doesn't "need" a matched pair of output tubes, or have MESA just not had time to catch up in making these available in time for the new amp's launch :?: The fixed bias thing makes us reliant on MESA-branded tubes, so I'm kind of interested to know what the score is here.....

p.s. I'm obviously hoping I won't need replacement tubes any time soon (especially as I still have about 3 weeks waiting time to get my amp ) - but these things are good to know :!:

 

[JAZZGEAR]

Well the amp can run at 5 Watts Class A, Single Power Tube. So, you are likely to wear the tubes at different rates...so matching them becomes a useless practice.

 

[recto-robbie]

Hey jazzgear,,, does that stand true for any amp that you can run different wattages??? For example my stiletto duece, it runs on 4 el34's but I can run it full 100 watts using all the tubes or I can run it at half power 50 watts using only two tubes.
I will continue to purchase matched pairs, but I never really thought of this. Any explanation or suggestions?

 

[JAZZGEAR]

Hey jazzgear,,, does that stand true for any amp that you can run different wattages??? For example my stiletto duece, it runs on 4 el34's but I can run it full 100 watts using all the tubes or I can run it at half power 50 watts using only two tubes.
I will continue to purchase matched pairs, but I never really thought of this. Any explanation or suggestions?

Possibly.....For example, on my Mark IV, if I run it in Simulclass/Pentode, Power switch up (for full power), then all four tubes are running at full power. But if I flip the power switch to tweed...and leave everything else aforementioned the same, all 4 tubes are still running but at a reduced power rate.

On the other hand, if I switch it to Triode...then only two of the four tubes are in use.

It really depends on each amp....But I suspect that your stilletto is just like the LSCs so that in 50 Watt mode only a pair of tubes are being employed while at 100, all four are online. The things get reduced in power when running them at each wattage setting in tweed mode -- same number of tubes online as aforementioned for each power rating but at a reduced power rate.

I think the tube matching is more important in full A/B class amp., Less so in a pure class A swithchable power, amp, like the Lonestar Special, 5:25, etc.

And finally, in your case, you'd want to continue purchasing matched pairs.....no need to spend the extra $$ for matched quads as each pair will wear at a different rate -- unless of course, you run at full 100 watt all the time...then in that case get the matched quad.

All of the above being said, however, if you're not buying Mesa tubes -- it may still be a good idea to get all your tubes matched, irregardless of power class.....to avoid problems.

 

[Digirat]

Well the amp can run at 5 Watts Class A, Single Power Tube. So, you are likely to wear the tubes at different rates...so matching them becomes a useless practice.

That makes sense - should have thought of that Saves some money too :!: Thanks for de-confusing me.