Cascode input on hoso56T

[bruno]

Well while I start the build of my long waited princeton reverb, which I'll be using a lot around the house. I'm also preparing to try the hoso build afterwards, and decided to ask for help, regarding the cascode circuit, which I would like to use instead of a pentode at input.

I'm thinking about using either a 12ax7 or a 12aut, and my main goal here is to simulate the gain of an EF86 pentode.

I included a simple copy paste I did, and I'm hoping you guys can throw some ideas at me. Obviously there will be some considerations and calculation I'll have to make gain wise, power rail wise, etc. so I'll take what you guys can help me with a work from there.

[The_Gaz]

You need Merlin's preamp design book -it's got a whole section on cascodes. I think he could answer just about any question could possibly have. The only thing that's tricky to simulate with the cascode is the EF86's high input sensitivity. The way it's set up in a Vox (which is what nearly every company copies) is such that the guitar can actually overdrive the EF86. Merlin has some tricks to get approximate this, and I'd be tempted to just give said tricks to you, but my book is on the other side of the country. BTW, he talks about 12AX7 vs. 12AU7 as cascode.

[tubenit]

I've read mixed reviews on how well that actually sounds like a pentode. Some favorable and some not. I haven't tried it myself, so I'm curious about how you like it?

with respect, Tubenit

[HotBluePlates]

I know you want to do the cool, tricky circuit. I myself had wanted to do a cascode circuit a while back (never did get around to it).

But you can do the same thing, with less parts (and maybe a cheaper tube) with a pentode. Or cascaded triodes, which offers very much more gain.

Sometime in the near future, I'd like to delve into the pentode preamp a bit more, just to compare various pentodes, and use up all the 6AU6's I have laying around.

[bruno]

The carr artemus seems to sound nice, it uses one 12AX7, implemented as a cascode.

I'm just not sure if my values of gain on the cascode are those of a EF86 pentode's gain, that's where I needed some guidance.

The problem here in europe and in portugal even worse, is that there is no way to have easy access (without spending lots of cash) to a steady stash of oddball pentodes, so the EF86 is always the best choice and most times current production ones, and eventually microphonics end up being an issue with most, if not all f them.

By the way here are some demos of the artemus:

Carr Artemus

Carr Artemus 1x12 with Fender CS Tele

Carr Amps Artemus - Billy Penn 300guitars.com

[jojokeo]

I've been planning on building something based similar to this for a while now. After making 7 various pentode-based designs and one cascode, my Firecracker amp utilizes a similar topology of the Firefly's input. It can be a bit noisy when full up but what amp isn't when really high gain territory is being used? But by having this switched and w/ seperate gain controls it can be tamed/controlled nicely. I put a preamp out on it and pipe it into various power stages and it puts out a very strong signal. As I recall there's 3 basic cascode circuits that can be used w/ various advantages (some w/ possible drawbacks too) and uses for each. If wanted it gets a great Marshally crunch w/out using a CF stage & yet retains the original guitar's tonal personality very well. My main computer decided not to start up for me after 7 years of reliable service so I can't provide any more info to you right now until I finish building the new one & transferring all of the data & software (what a PITA).