EL34 amplifiers are a little trickier. I know a lot of people
that believe you can just swap out EL34’s with KT88’s
and re-bias. While I’ve seen people do this with no
problems, I don’t recommend it. Most EL34 based amplifiers are going to require a change of the bias feed
resistors from 220k to 100k. The K T88 (and 6550 for that
matter) can’t quite deal with the higher grid resistance
from the 220k resistor (these are typically the rating
found in EL34 circuits). Not changing it will both shorten the life of the tube (probably dramatically) and also
not allow the KT88 to be run close to their design ratings. In other words, if you don’t change these resistors
out, the K T88 will not perform well and may not sound
good at all. As with any other tube swap, make sure the
rest of the circuit is designed to accommodate them.
Your tech or manufacturer would be able to tell you.
Please do not try to swap the K T88 out with 6L6 or 6V6
power tubes. If you have an amp with these particular
tubes, check into a KT66 instead and as always check
with your technician or the manufacturer before swapping any tube. This week’s article is geared toward the
more advanced electronic hobbyist or technician so
please make sure you know what you’re doing before
attempting any of this. The mods are simple to me
but I have over 14 years of experience in electronic circuits and have done this a few times to say the least.
If you haven’t experienced the raw power and tonal
bliss that can be had from a KT88, I highly recommend it. It may be perfect for you and it may not be
but the mods are fairly simple and easily reversible. So
that’s it for this week folks, short and sweet. Thanks
for reading and we’ll see you next time, in The Corner.
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