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Old 10-07-2021, 09:54 PM
Isaacc7 Isaacc7 is online now
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Join Date: Oct 2020
Posts: 146

Originally Posted by Analog Addict View Post
I don't remember what the KT88 uses for driver tubes, but if you're looking to switch from say a 6SL7 to a 12SL7, it's not really possible without changing or adding a new filament transformer. Tubes like a 12AX7 or 12AU7 can be used with a 6V filament transformer because of an extra connection in the internal filament wiring that can then be used to wire the tube socket in either series or parallel, allowing the use of either a 6V or 12V filament transformer. However, 12SL7s don't have this extra connection, so the corresponding flexibility is missing.

I can't exactly speak for Dennis, but his time is so limited trying to keep up with demand on existing orders and models, that I doubt he will be interested in messing with a one off like what you are proposing. Someone else might be able to do this 6V/12V switch for you, but it would require not only adding at least one (if not two) extra filament transformer(s), but also some additionally switching circuitry...
I didn't really expect Dennis to want to do it but was hoping someone would talk about the complexity involved. So thank you!

The KT88 uses the 6bx7/6sn7/6sl7 so it sounds like it would need a new filament transformer. I assume that the filaments of both the input and output tubes are run off of a single tap on the power transformer. Would changing just the input tube mess up the heaters on the output tubes? I've asked a few local repair places but haven't heard back yet. Sounds like this may not really make much sense money-wise.
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