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Old 3rd October 2007, 10:12 PM   #1
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Default help with KT88 / mikaels SE amp

sorry for constantly asking questions but,
i am trying to design a kt88 based single ended amp i have been looking a lot at mikaels kt88 design which seems to have had good things said about in this here forum. however im trying to work out whats going on.

i recently posted a question asking about line level and ended up being told that it varys alot but a good place to start is about 1Vrms input .

i then checked out the curves for the 6n1p driver stage valve mikael used and found that in his setup an input voltage of 1Vrms would result in an output of about 80V pk-pk. (if anyone would care to confirm this twould be cool).

anyhow 80v pk-pk seems far to much (i was told about 40-45V pk-pk) to send in to the kt88 especially in ultra-linear mode.

is mikaels amp just designed for a lower input ?



any thoughts greatly appreciated,,,
also if im wrong in any way let me know
cheers
soundbadger
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Old 4th October 2007, 12:52 PM   #2
Sherman is offline Sherman  United States
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The 6N1P is capable of supplying more voltage gain than is strictly needed by the KT88. However that isn't a bad thing. Seldom do you want the driver stage in a hifi amp running at full output where distortion will be high.

Having headroom in the driver is good as is having headroom in the output stage.

I've built Mikael's schematic and really like it. I'm running things a bit hotter than the schematic calls for (424V B+, 82mA on the KT88). I'm getting between 7 and 8 watts and the sound is very good. I'm also using James 6123HS OPTs which I think are an excellent value.
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Old 30th September 2010, 09:59 PM   #3
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As a follow up question, the mikeal amp would need about 200mA of DC current. I have a Hammond 374Bx rated at 175ma (375-0-375V). I think this is probably the current rating for the whole of the secondary and can probably deliver twice the current for the half. Would this transfomer be sufficient.
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Old 30th September 2010, 11:08 PM   #4
mach1 is offline mach1  Australia
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The current rating is for 375V into a cap input psu (ie 375V x 1.4). I would not use it for this application.
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