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Old 4th June 2009, 01:50 PM   #1
JC951t is offline JC951t  Taiwan
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Default OPT linestage question

Hi Guys,
Curious question.
Can we use an OPT from an SE amp to make a linestage ?
Don't know much about OPT design but I believe it's got to do with gain. Now what if the tube in question has lots of gain. Is
it doable ?

Many thanks
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Old 4th June 2009, 02:23 PM   #2
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Hi,
Could you please be more specific? mu and Ri of the tube is needed. If you already have an OPT, the primary and secondary impedance and primary inductance are needed?
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Old 4th June 2009, 02:58 PM   #3
JC951t is offline JC951t  Taiwan
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Hi Revintage,

Most linestage OPTs are rated with an output impedance
of 600 ohms. Amp OPTs are 4,8 or 16 ohms. Assuming
that the input is 5K & using a 6n6p, would it work as a
linestage? If gain is too low, we can add another input stage.
Ofcourse this would turn it into an amp. Sorry if it sounds stupid I'm just curious.

Thank for the advice
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Old 4th June 2009, 03:26 PM   #4
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With 5k:16ohm you would get a gain of ca 2dB. With a 2,5k:16ohm you would get ca 2dBs more. But in order to get it to work, primary inductance should be at least 50H.
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Old 4th June 2009, 03:41 PM   #5
JC951t is offline JC951t  Taiwan
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Thank you revintage
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Old 4th June 2009, 04:31 PM   #6
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hey-Hey!!!,
A 5k:16 is 17.7:1 step-down. Less than unity gain there with 6N6Pi loaded by 5k. Aside from step-down ratio, there is no issue with such devices for linestage use. The secondary won't likely have a speaker-level load applied, so the primary is mostly loading the tube with its inductance. For well-biased triodes, this is not such a large issue as it might appear on first inspection.
cheers,
Douglas
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Old 4th June 2009, 04:47 PM   #7
DougL is offline DougL  United States
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As revintage has stated, with enough primary inductance, it would work.

Transformers are an item that have so many compromises that they really need to be optimized for the application in order to be their best. This transformer you are using is going to be much larger than necessary and will have larger stray capacitance. This may compromise the high frequency response.

Good Luck with this.

Doug
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Old 4th June 2009, 05:16 PM   #8
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Hey Douglas,

The "minus" got lost in transition. So we agree! Anyway donīt see a 5k as an option so 2,5k:16 ohm could be OK. Even if itīs just 2dB gain with 6N6. Better to go for a 5842 or 6C45 with higher mu.
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Old 4th June 2009, 07:56 PM   #9
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Quote:
Originally posted by revintage
Hey Douglas,

The "minus" got lost in transition. So we agree! Anyway donīt see a 5k as an option so 2,5k:16 ohm could be OK. Even if itīs just 2dB gain with 6N6. Better to go for a 5842 or 6C45 with higher mu.
hey-Hey!!!,
Seems about right... I'm currently enjoying PP 6S45 loaded with 20k:600 ( both CT ). Gain is around 5:1 at wide open volume.
cheers,
Douglas
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Old 4th June 2009, 08:16 PM   #10
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Yo Doglas,

A transformer shouldnīt be specified with Z:Z. Better to specify n:n together with primary inductance. What do you think?

Your transformer is 20k:600. It could as well be 2,5k:75 or 80k:2,4k if it wasnīt for inductance.
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