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RE: Are my ITs ok for this schematic?

Posted by Tre' (P) on August 21, 2014 at 16:55:04

In Reply to: RE: Are my ITs ok for this schematic? posted by DAK on August 21, 2014 at 16:13:54:

A 1:1 interstage transformer will have a reflected impedance impressed on the primary that is the resistance (or impedance) connected to it's secondary but that's not the end of the story.

Even if the transformer is stable without a "load" on it's secondary (most transformers have resonance problems if not loaded) there needs to be enough inductance to "support" the rated impedance of the primary.

(Transformers don't really have impedance's. They just have winding ratios, inductance and winding capacitance. Transformers have impedance's that they are meant to work with.

I believe the impedance ratings on transformers tell us about the inductance of the primary and the impedance ratio between primary and secondary.)

80Hy has a reactance of 10k ohms at 20Hz.

A 6sl7, with it's plate in parallel, has a plate resistance of about 22k ohms.

To keep harmonic distortion low a triode needs to see a load impedance of at least 3 times it's own plate resistance.

A 5687 has a plate resistance of about 2.5k ohms.

I believe the transformer you have described should work if driven by a 5687.

For a 6sl7 to be "happy" with the load, I believe the primary inductance of the IT should be at least 400Hy.

I don't think a 6sl7 is well suited for driving IT's.

Tre'

Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 08/21/14 08/21/14

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