Ef 86?????

[hasserl]

FWIW and as a side note to this topic, a very cool input stage is both triodes of a 12AX7 run as a cascode to approximate the gain of a pentode. A single 12AX7 cascode into a LTPI driving a pair (or quartet) of EL84's makes for a very nice amp!! Check this schematic for reference: https://taweber.powweb.com/store/smokeII_schem.jpg

[jrfrond]

FWIW and as a side note to this topic, a very cool input stage is both triodes of a 12AX7 run as a cascode to approximate the gain of a pentode. A single 12AX7 cascode into a LTPI driving a pair (or quartet) of EL84's makes for a very nice amp!! Check this schematic for reference: https://taweber.powweb.com/store/smokeII_schem.jpg

That is something I've always wanted to try as an alternative to the sometimes-finicky EF86's. Have you ever tried this? I want to know what it sounds like and more importantly, FEELS like.

[hasserl]

That is something I've always wanted to try as an alternative to the sometimes-finicky EF86's. Have you ever tried this? I want to know what it sounds like and more importantly, FEELS like.

I haven't personally, but my brother did this. He built that Smokin Joe II circuit into a 5E3 chassis/cab he had using the stock Weber 5E3 trannies (Blue Dog speaker). I played thru the completed amp and was very impressed with it. I used a Tele and went thru every combination of settings. IMO you can leave off the MV, the magic in that amp is the entire circuit combined, not the preamp/PI alone; without the EL84's in the mix the tone suffers. (If you need to lower the volume I recommend an attenuator) Very nice cleans when rolled back, great OD when pushed, nice tone from clean to dirty. I highly recommend it. And in fact that amp has really pushed my LTPI buttons for my 5E3X2 that I posted about earlier in this thread.

[MattT]

Hey hasserl,
I was considering building a DC30 type amp but with something else instead of the EF86. Using both sides of a 12AX7 yields opposite phase as one EF86...does the cascode just flip the phase once?

[hasserl]

Hey hasserl,
I was considering building a DC30 type amp but with something else instead of the EF86. Using both sides of a 12AX7 yields opposite phase as one EF86...does the cascode just flip the phase once?

I believe the answer to that is yes, the phase of the output is inverted vs the input.

[jrfrond]

Here's something of interest I found in a Google search concerning Cascode Amps:

"The Cascode amplifier works by realizing all of the bottom triode's transconductance by isolating it from the plate resistor and load resistance. This allows the grid to fully control the current through the triode and thus define a gain across the plate resistor. This increased gain, which can easily exceed the amplification factor of the triode, comes at a price; increased distortion and virtually no power supply rejection (PSRR). This circuit enjoyed great popularity during the 1980's. Today, the circuit is not as popular, as it often makes for a more transistor-like sound. Still, it remains a good choice when low input capacitance or high gain is required."

[garyk]

EF86s can sound warm and full.

There are also "low noise" versions (6BR7 or some-the-such) but they have different pinouts.

There are other pentodes you can check out, a lot of more obscure ones are cheap.

For a bit of a challenge, try a little miniature: I used one in a tube mic
circuit (fits inside the mic) and it sounded very good.

Will later experiment with these for tube pedals...

I also like lower gain triodes, I use a few 12AZ7s rather than 12AX7s in many amps.

[Steve Conner]

I hate to sound like a nerd, but hell, I am a nerd! The 12AX7 circuit posted is not a cascode. It just uses the top triode as a current source load for the bottom one. (A real cascode would supply the top triode's grid with a constant voltage, as if it was the screen of a pentode, and take the output from its plate.)

So, while it may have more gain than a 12AX7 with a regular plate load resistor, it'll still suffer the same treble loss from Miller effect that a triode has.