Pentode preamp gain stage

T-Rex

T-Rex

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Anyone try a pentode as a true preamp gain stage? I am talking other than a EF86 Vox, of course.
 
Ok imgur changed since a few months ago that I was last there to post an image and I need re-schooled on a how to, please
 
Dang, T-Rex! I wish I knew a whole lot more on what you’re talking about, but it does sound interesting. I tried to research some info on it, and I can honestly say that: Yup, it’s way over my head, ha ha! The following short thread from EL34 World might have some useful info for you though:

pentodes and triodes in preamp

Hoffman Amplifiers Tube Amp Forum, pentodes and triodes in preamp
el34world.com

Interested to see where you go with this.
 
I used some 6197's a few years back. It's roughly a 6CL6 equivalent.

I thought they sounded nice but not a ton of gain in my application.

They're probably something I should revist as they are dirt cheap.

If you like, I can send you a few NOS sleeves.
 
From what I was reading the pentode such as a EF86 or 6267 has more gain than paralleling two triodes and slightly less than cascading two 12ax7 triodes. The harmonics are supposed to be noticeably better. In reading the Valve Wizards take he says the output impedance can go high so it's a better application if the tube is followed by a tone stack.

I'm not sure if that is why the EF86 in a Vox often had microphonic issues because maybe it needed more of a load ?

I was interested in a better tone than a typical CF in a Marshall produces.
 
As an experiment built a AC-15 Vox sort of channel one and a Marshall second channel with master volume 18 watt
Radio Spares clone transformers on the EF86 channel 500K volume control and a seven position rotatory switch capacitors as used
in the Dumble Steel String Singer for a tone control simple but is a harmonic generator compared to the Marshall channel TMB
The EF86 likes 90 volts on the 220K plate resistor the best sounding EF86 I found was a 1965 Mullard UK made.

EF86 TMB 18 Watt 003.JPG
EF86 TMB 18Watt 002.JPG

BN_FOXY18_v3_0.jpg
 
67plexi said:
As an experiment built a AC-15 Vox sort of channel one and a Marshall second channel with master volume 18 watt
Radio Spares clone transformers on the EF86 channel 500K volume control and a seven position rotatory switch capacitors as used
in the Dumble Steel String Singer for a tone control simple but is a harmonic generator compared to the Marshall channel TMB
The EF86 likes 90 volts on the 220K plate resistor the best sounding EF86 I found was a 1965 Mullard UK made.

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Thanks for the tip.
 
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