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Old 5th February 2013, 08:25 AM   #1
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Default KT120 triode operation single stage amp

hi i need consulting to projecta serious curious ampo

input: one for 10 times transformer lundhasl, one kt 120 triode cathoiode bypass poliproylene, output transformer lundhal about 3 k ohm.
Chocke inductive PSU with poly caps 100 microF for channel.
Power transformer: one for 400 VA.
Expedcted 15 w class A2, with damping factoer of about 4.
cabinet : tin search of aggod one for a few bucks , if yopu know one pleas e tell me,

do you think it casn be work?
thanks to all expert for precious suggestion .

by , inertial
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Old 5th February 2013, 01:10 PM   #2
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What sort of pre-amp are you planning to use, ie, how will you drive the 1:10 step-up transformer?
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Old 5th February 2013, 05:40 PM   #3
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Sorry, you are right.
I have total missed to mentione that the input goes into a Lundhall 10x gain transformer.

Thanks.
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Old 5th February 2013, 05:44 PM   #4
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Quote:
I have total missed to mentione that the input goes into a Lundhall 10x gain transformer.
I think you did actually mention that. The thing is you need something with a very low output impedance to drive the 1:10 step up transformer. That is I think the reason Erik asked you how will you drive it. I.e. what preamp are you planning to use?
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Old 5th February 2013, 06:49 PM   #5
tinitus is offline tinitus  Europe
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wouldn't there be a limit to how hard you can drive a low signal input/step up trafo
or else I guess it would need be a much bigger interstage thing
and the signal needed to drive a KT120 directly would be ...'substantial'... I guess
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Old 5th February 2013, 06:55 PM   #6
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Quote:
wouldn't there be a limit to how hard you can drive a low signal input/step up trafo
Yes. But depending on his setup it could be usable. For instance. Kees Soeters uses a Lundahl 1:8 stepup in his 300b amplifier.

Burmester or something preamp with low output impedance -> 1:8 transformer -> 27 -> 300b. And that works fine.

The KT120 is easier to drive than a 300b. So it might just work.
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Old 5th February 2013, 08:10 PM   #7
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Originally Posted by Bas Horneman View Post
The KT120 is easier to drive than a 300b. So it might just work.
Don't think so. It is a Pentode, so you need feedback.
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Old 5th February 2013, 08:19 PM   #8
Tesla88 is offline Tesla88  Italy
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It's a Pentode, but OP want to use it as triode , aniway triode = less gain , so I don't know if a x10 x Former (model not mentioned ) woul be enough to drive a Kt120 at full , and yes you need a good preamp to drive a step up transformer , something able to drive a 600 ohm load ...
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Old 5th February 2013, 08:19 PM   #9
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It is a Pentode
So is an EL84. And it is very easy to drive.

But I have to admit I ASSUMED the KT120 is easier to drive than a 300b.
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Old 5th February 2013, 09:18 PM   #10
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Whether KT120 or 300B....what you win in terms of gain, you loose in terms of miller capacity.

No matter how you look at it, a KT120 isn't really suitable for a SPUD amp. Use some high-gm video pentodes like 12GN7 instead and you will have more fun.
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