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Old 11th November 2013, 11:33 AM   #11
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Forgot to clarify, sorry.
Pentode mode, fixed bias, lean AB1.
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Old 12th November 2013, 03:14 PM   #12
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Bump? Somebody must have used those.

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Old 12th November 2013, 04:48 PM   #13
rmyauck is offline rmyauck  Canada
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I know Jim McShane doesn't recommend them in the HK Cit II with it's I believe B+ of 470 + depending on line voltage. Rich just said 460V so he could use the 6550 group so maybe a little less to be safe.
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Old 13th November 2013, 07:09 AM   #14
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Location: Alps:Tube amp designs over 150W, SMPS guru.
Go for the same curves as per KT88 (tempting to say KT66) but back off the curve at 33W dissip, even though the data sheet quotes max plate dissipation at 42W..These new tubes don't like higher and with lower 450V B+, rules out 100W power per pair. I run each at 75mA quies max for a bit more class A at low listening levels and have a couple of amps with such that give distortion comparable to KT88's. With some ears one can reduce the quiescent even further.
A pair on 75mA I quies each will on max signal give peak current of ~130mA (each) on music equating to around 65W more.
The TungSol new edition can't take the duration when compared to the to the famed GE 6550A; that tube was practically a KT88 straight swap.

pic of 3 tubes, A GEC KT88; 6550A JAN; New Edit Tungsol 6550.
Of the 3; the Tungsol has the smallest area anode. You won't find a 6550A in catalogues without a having big wallet. Out of the 3, it has the largest area anode.

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File Type: jpg 88-6550A Tung.JPG (149.5 KB, 143 views)

Last edited by richwalters; 13th November 2013 at 07:11 AM. Reason: correction
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Old 16th November 2013, 07:43 PM   #15
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this is the 6550 curves at G2=300V , the red dots are 33 W Pa max.

Looks awkward, I cant go to the knee without exceeding 33WPa.

Click the image to open in full size.
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Old 16th November 2013, 08:10 PM   #16
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Click the image to open in full size.

Same with KT88 curves. What am I missing here?
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Old 17th November 2013, 10:08 AM   #17
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Location: Albury NSW Australia
Default Hey Read these threads

6SL7 SRPP / KT77 Push-Pull Class-A Ultra-Linear DIY Tube Amplifier
OddBlocks - Class-A Push-Pull KT88 Tube Amplifier (12SL7 Driver)
DIY Audio Projects Forum • Oddwatt Push Pull Tube Amplifier Projects
This is an interesting implementation of a range of tubes
Good luck
"Better to say nothing and keep them guessing than to speak and remove all doubt."
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Old 17th November 2013, 01:32 PM   #18
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Not really. Read #11
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Old 17th November 2013, 01:38 PM   #19
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Try lowering the screen voltage, otherwise it would be difficult to get below the plate dissipation limit without changing the plate voltage and/or the OPT.
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Old 17th November 2013, 04:42 PM   #20
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I have not ordered the transformers yet. This is a tentative load line, just to make my point. So it can be any suitable value.
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