MT15 5881 Can I swap in 6L6GC's?

[surjer]

I have my buddy's MT15 that I have been checking out and love it. I am considering ordering one. However, the new ones come with the 5881's. I am wondering if i for some reason do not care for the 5881's can I swap in 6L6GC's in it or is there more to it than a simple tube swap?

Thanks in advance and sorry if its been asked 100 times. I searched but didnt see that anwered clearly.

 

[andy474x]

Yes, you’ll just need to bias with a multimeter. Very easy.

There have been a few small changes/revisions to the MT15 circuit, but I don’t believe any that change the ability of the power section to run 6L6 or 5881. Mostly just tweaks to reduce noise, etc.

 

[gamjamm]

Good rule is to bias anytime you replace power tubes. General rule is you can use a 6L6 in place of a 5881 but not always the other way round. A true 5881 {like the Tung-Sol used in the HDRX-20 dissipates a max of about 23watts while a 6L6 dissipates at least a max of 25watts. A 6L6GC dissipates about 30watts. There are exceptions to both types. Also, amps are usually biased from 50% to 70% of the max dissipation. So, if your RCA NOS "blackplate" 6L6GC's are biased to 70% {pretty hot}, and you throw a set of 23watt 5881's in, they may red-plate or not last very long without a re-bias. There are some mil-spec 5881's that can handle higher plate voltages very well like the 5881/6L6WGC, the 5881WXT+, the 6p3s-e, and some NOS 5881's. It depends a lot on the amp design and particular voltages/power supply/ tranny used.