Amp running 4xel84s with really low plate voltage!

[bruno]

Ok it's time to build again and I guess as usual I need a little help to start defining what the amp will be.

I've been trying out different amps and although I can always find something I like about a fender, a marshall, a vox, or some other less known, or oddball amp. I think the amp which has the most aspects about it's sound and response that I like is the Vox ac30.

I do however like the high fidelity of a typical blackface fender tonestack.

A few months ago I got a hold of an alessandro bluetick, which uses 4xel34 at a plate voltage of 230V (which is really low). The amp has a few other details, such as an ultra linear output section. But it does sound like a big 4 output tubes amplifier, only at much more manageable levels.

I was wondering if it would be a good idea to build an ac30, but using a real low plate voltage something like along 200 volts on the plates and higher idle current. Or am I better of sticking with the classic ac30 output?

[jojokeo]

You ask yourself a few questions of what you want to achieve. Are you looking for certain characteristics, need maximum output power, do you only have a certain PT to work with, etc.? It's pretty cool the flexibility you have working with various voltages and still be plenty fine. Tubes work well w/in a pretty wide range of voltages. Now you might want to compensate a few things like a lower value cathode resistor to acheive higher power dissipation than if you went with the standard values, same on reflected impedance w/ the OT. But again, there's a range where you'll hardly notice in the tone or output dept. Ofcourse your dropping resistors on your power rail to the other nodes will be less to so that you don't drop as much voltage as you otherwise would. A big thing I notice when using a lower voltage is that the amp is much quieter at idle than when ran at a higher voltage.

[bruno]

I'll buying some Edcor iron (as recommended by some of you guys), for the project, so I have no limitation regarding the PT I'm using, I can choose based on the design itself.

I think it will be cool to build an amp running on lower voltages, like the alessandro does. It will be healthier for the tubes and I'm hoping to get the same 4xel84 output stage response but with much lower output.

[6G6]

No doubt the lower voltage approch will yeild some interesting results,
but the AC 30 gets some of it's vibe from the fact that it is running on the high
end of the voltage range for EL 84s.

[bruno]

I have mixed opinions regarding what this next amp will be... I have a nice 65 Vox ac30, that I must sell, it's big and loud, but I can't justify keeping it. Love it's sound though. AC15s, just don't sound the same, but I also love some of their character.

So I guess I'd like something with an AC30 midrange and punch.

I love the idea of running tubes at a lower voltage.

Plus I've been wanting to try the geezer's and tubenit's take of the hoso56 amp. I've been reading about cascode 12au7 inputs, and I was set on trying this in the hoso circuit in place of the ef86.

I'll have to try and come up with something that incorporates all these aspects.

Economy is kind of bad in this part of the world right now (Portugal), so I'm weary about spending money on a set of transformers for a low voltage amp, only to find that I actually like the results of a regular ac30 set better. But then again if I don't experiment I'll never know.

[bluesbear]

Although I've been told that my reasons are theoretically wrong, I never run EL84's above 300 volts. At lower voltages, they sound much warmer and smoother. My description is violin-like. It always works like that for me and results are worth 10,000 theories to me.
Dave

[plexi50]

I have a quad of El84's running with a 380 VDC plate. I think they sound great. I did build an amp a while back that had 2 of them running at 325 VDC. They sounded good as well.  Sometimes it's also a matter of what power transformers i have laying around.  I dont always have exactly what i would like to use

[bruno]

I'm thinking around 220V-230V on the plates...

I always liked how geezer, tubenit and the rest of you guys gathered ideas for the hoso56, and I'm curious about that circuit, so I'll work from there and see what happens.