295 Power Amp Tubes - KT88?

[HSL]

I got a new 295 and it came with EL34s in the outer sockets and KT88s in the inner sockets. From a brief search of the forum I'm reading that it's not good to put KT88s in a Mesa amp, but I'm not sure if it's ok for the 295 power amp in particular.

I'm thinking of taking out the KT88s and putting in a new quad of regular Mesa 6L6 tubes. I'm thinking of taking out the KT88s and possibly throwing them in my old dual rectifier, but I'm not sure if the dual rec. will take KT88 tubes either.

 

[94Tremoverb]

I haven't tried this, but there is very little reason it shouldn't work, at least in theory. KT88s have higher voltage and power dissipation ratings than either 6L6s or EL34s, draw about the same filament current as EL34s, and require about the same bias voltage as 6L6s - so they should be OK in an amp that can use *both* types, though not necessarily one that uses only one of them. Make sure you set the tube selector for 6L6s.

If you can, check the current draw and calculate the plate dissipation. The only real danger I can see is that the plate dissipation could still be within the tube rating (which is almost double that of a 6L6 or EL34) and so not damage the tubes, but put enough extra load on the power transformer that it may overheat. My Tremoverb runs very hot with EL34s anyway... I would be a little worried if the transformer got any hotter.

I would defer to anyone who has tried it though!

 

[crane]

Eurotubes sells a "replacement kit" with 4 EL34 and 4 KT88 for the 295.
KT88 draw just a little more heater current than the EL34, so they could fit in a dual rec, but it surely need a rebiasing for not to overload the output transformer.
I don't know specs of the power tranny of the 295, but KT88 draw waaaaaaay more heater current then the 6L6GC, about 0.7 to 0.9 A each. So it's about 3A more load for the power tranny on the heater section, really don't know if it can afford it without any trouble ! I personnaly won't try it with mine !

 

[94Tremoverb]

Exactly... the filament current is why I would not use them in an amp designed *only* for 6L6s. But in an amp that can handle EL34s, as long as it also has a bias setting for 6L6s - as the Dual Rec does - it should be at least close.

 

[HSL]

All compatibility aside, I'm wondering what the tonal differences or sound differences are between the KT88s and the 6L6s. Actually - this'll give it away that I haven't fooled around with it much, but I'm not even sure of the tonal differences between EL34s and 6L6s. I'm going to have a standard combo of 6L6 and EL34 tubes in the 295 and see what it's like.

 

[talltxguy]

Eurotubes sells a power tube package for the 295:

Full Retube for the Mesa 295 KT88 option
Price: 254.00
Description: Includes a matched quad of the JJ KT88's and a quad of the JJ E34L's in a hotter grade to get that cold factory bias up a little and four matched and balanced ECC83S's for the front end. In this kit the KT88's are run in the four middle sockets in place of the 6L6's. This gets the bias up whre it should be and the result is a MASSIVE warm sound!

I'm not the biggest fan of JJ preamp tubes, but I have consistently used Eurotubes' package deals for my 50/50 & my 20/20 & thought they sounded better than stock Mesa power tubes. I plan on trying the KT88 option for my 295 in a few months, but right now I'm running Mesa power tubes just because I want to get an idea of what they're like so I can have a basis for comparison.

 

[HSL]

I'm starting to wonder if what's in the 295 was actually purchased from Euro Tubes because that's what it's looking like.