Tell me about my tubes....

[sbalderrama]

So, finally got around to checking what power tubes are in the IIC+ and Mark IV I acquired recently.

IIC+ had Phillips 7581a's, non mesa label in the outer sockets, and STR 420's in the inner sockets. After playing around a bit, I've decided that I like both the class A and simul modes better with the 420's on the outside and he 7581's on the inside. I noticed that the MIII manual notes that Mesa recommends EL34's in the outer sockets due to tube durability issues; has anyone noticed a problem with that?

The Mark IV has a quad of STR 430's.

Whats the general consensus on these tubes? Would it be worth trying a quad of 440's in my IIC+ if they are close to the original 415s? Does Color matter if I get 440's for the C+?

Thanks.

 

[Russ]

The Phillips 7581A is a nice tube. I have a quad in my Dual Rec. I have a quad of 420's in my Mark IV. The 7581A gives my Dual Rec a tightness and clarity that I haven't found in other tubes that I have played in Dual Rec's. The 420's in my Mark IV are so sweet I don't really want to change them. I haven't tried the 430 yet.

You will be hard pressed to find some new 415's. Then again they have a life of something like 10,000 hours so even a used set wouldn't be too bad if not trashed. I don't think the 440 would compare to that. Color code will matter for texture. Refer to the color code posts as I cannot remember offhand without consulting them myself.

If I am not mistaken the outer sockets are usually where you will put the other than 6L6 types with exception to the 6V6's in a Mark IV that you must load all 4 sockets with the 6V6's.

 

[JOEY B.]

I noticed that the MIII manual notes that Mesa recommends EL34's in the outer sockets due to tube durability issues; has anyone noticed a problem with that?

The way that it was explained to me is that after MESA stopped using the Sylvania 6L6, they did not have a 6L6 that stood up too well to 480 plate volts and the -46V bias on the outer sockets of their simul models. The STR-440 has given them a new ray of hope as far as 6L6 durability.

Would it be worth trying a quad of 440's in my IIC+ if they are close to the original 415s? Does Color matter if I get 440's for the C+?

Yes and yes.

I have been told twice now that the "red" STR-440 is the only color to use in the outer sockets of a simul C+ with the "105" power transformer. You could use red, yellow, or green ones safely in the inner sockets. This info may ONLY apply to the "105 Simuls", be it a MkII or very early MkIII, I do not know for sure. I just know what I heard. If the question involved a later MkIII or a MkIV, the answer may not be the same.