KT66 voltage gain?

[ygg-it]

Hello which is the mu (voltage gain) of KT66?

I cannot find in any datasheet.

I just think it is a little bit less than EL34 (mu=11).

My guess would be 10.2, hence KT66 needs a pre amplification 7% higher than EL34.

 

[JonSnell Electronic]

An EL34 has a gm of 11.0 and the KT66 6.3.
The 6L6 has a gm of 5.2

 

[Ketje]

An EL34 has a gm of 11.0 and the KT66 6.3.
The 6L6 has a gm of 5.2

So the EL34 need allmost half the drive voltage compared to the KT66, if the conditions are the same.
Conditions are load and bias.
Mona

 

[ygg-it]

So the EL34 need allmost half the drive voltage compared to the KT66, if the conditions are the same.
Conditions are load and bias.
Mona

Thanks but sounds strange. I'm not testing such a volume decrease changing KT66 instead of EL34 in the same amplifier. Just a little bit less but not half.

 

[JMFahey]

Thanks but sounds strange. I'm not testing such a volume decrease changing KT66 instead of EL34 in the same amplifier. Just a little bit less but not half.

Does your amplifier use NFB or is it open loop?

 

[6A3sUMMER]

I agree with the question JMFahey asked.

Generalization:
1. There are very few open loop characteristics including gain, that can not be at least partially "hidden" by using global negative feedback.

2. Exceptions, yes. But refer to # 1 first.

 

[ygg-it]

Does your amplifier use NFB or is it open loop?

heavy GNFB, thanks

 

[audiowize]

Heavy GNFB means that you're not likely using the KT66 triode wired, so the triode mu wouldn't be useful.

Amplification factor of a KT66 in pentode is RL*gm. Ultra-linear is a different matter.

 

[Mark Tillotson]

Hello which is the mu (voltage gain) of KT66?

I cannot find in any datasheet.

Google found it easily for me: http://www.r-type.org/pdfs/kt66.pdf

I just think it is a little bit less than EL34 (mu=11).

My guess would be 10.2, hence KT66 needs a pre amplification 7% higher than EL34.

140 for pentode, 8 for triode from the transconductance and anode impedances...

 

[ejp]

heavy GNFB, thanks

So why should there be a volume change? The closed-loop gain is determined by the ratio of the feedback resistors, not by the product of the stage gains.

 

[6A3sUMMER]

Thank you ejp!
You said it way better than I did.

I already said that in my post # 6:
"There are very few open loop characteristics including gain, that can not be at least partially "hidden" by using global negative feedback."

I guess nobody understood because of how I said it.

Generalizations:

Lots of global negative feedback tends to make an amplifier sound the same, even when you change the stages
that are in-between the feedback loop.

Tube rolling is not half as revealing in an amp that has high levels of global negative feedback,
versus tube rolling in an amplifier that has no global negative feedback.

The owners of amplifiers with high levels of global negative feedback who decide to tube roll say: I can not hear a difference in Gain, in distortion, in frequency response, etc.
. . . Surprise!