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Message started by Brian on 09/18/20 at 08:16:42

Title: Interstage Transformers with the Pentode?
Post by Brian on 09/18/20 at 08:16:42

Are ITs useable in the single ended Pentode amplifier?
I have only seen them used when the final tube was a triode. Does the Pentode have the wrong impedance, or some other objection for transformer coupling to the drive stage?

Perhaps pentodes came on the market at the same time as ITs were going out, so IT coupling was not done with pentodes back then and is therefore not traditional, so nobody does it today.

Anybody know?

Brian

Title: Re: Interstage Transformers with the Pentode?
Post by Lin on 09/18/20 at 21:56:13

I found this from "Wavebourn" from gearslutz:

Lots of things happened since then: AC power, so higher voltages become available for resistive load; minimum 20 dB of extra gain for global negative feedback; new cheaper materials for high quality capacitors; pentodes that did not need such power to drive like triodes needed; records with extra octave on highs (16 KHz instead of 8 KHz); run for linearity instead of smoothness. The later is most significant: if does not matter which order of harmonics to measure to get low sum of them, extra gain and feedback is preferable than very expensive interstage transformers.

and "drtechno" from same thread:

The primary reason why interstage transformers are not typically used today is the cost of manufacturing and now a days, there is so much verity of electronic components that can be used to get around designing a circuit with an interstage transformer....

Some info here:

https://ankaudiokits.com/2/agrove_interstage.html

Title: Re: Interstage Transformers with the Pentode?
Post by Brian on 09/19/20 at 06:14:32

Hi Lin
It is interesting that you posted that.That is the page I read which caused me to ask the question!

If an IT can work into a Pentode, I would like to hear it. I think it would add to the sound the same qualities transformers add elsewhere in the signal path. A more organic sound, more shimmer, more sparkle.

Brian