silly idea, possible?

[norburybrook]

Having spent a couple of weeks tweaking a new build and thinking about various amp related things I have a question, forgive me if it's a stupid one.


Is it possible you could have an output section of 2xEL84's and 1x 6L6 in the standard push pull config? Obviously having separate bias pots to control the required bias voltage for each side? or perhaps cathode biased??

My thoughts were perhaps the difference between the two would give an interesting(good) harmonic complexity in the sound.


M

[martin manning]

You could make it work, but I would question the value of it. Two EL84 combined have 24W plate dissipation so that would come close to a 6L6GC's 30W, but the anode voltage and the signal voltage to fully drive an EL84 are lower than for a 6L6. It would be much easier voltage-wise if you used equal numbers of EL84 and 6V6. If you have a small amp, all you'd need to try it out is a socket adapter and a separate bias adjustment.

[stephenl]

Stephenson Amplifiers has a similar config but opposite of what you're suggesting:

Stephenson.png

This was a build I did a while ago and is my favorite:
Very different from what you're suggesting, but in the theme of mixing power valve flavors...

LPS2 - PA.jpg

I ended up with an 8K primary OT with KT66's - the KT88's were a little too clean for me. It has individual bias pots so you could experiment quite a bit - I really like the sound of KT66's.
I've used both a KT77/EL34 and a 6V6 for the interstage driver. The KT77 drives the output harder earlier as you would expect. Both tubes in this position sound great but different. I'd like to try an EL84 in the driver position - need to build a noval to octal adapter.

Added benefits are no blocking distortion on power tubes and some extra protection if there's a bias failure...

[norburybrook]

thanks, That Stephenson looks interesting , when all 3 tubes are on you'd have an EL84 with the 6V6 on one side of the push pull and the EL34 on the other, not a million miles away from my 3 tube AB setup Are they all cathode biased?


M

[Stevem]

In my fooling Round with mixing output tube types there is very little difference in tone and responce until you start to drive the tubes into clipping.

Beam type output tubes like the 6L6 and 6V6 rev up faster then the EL84 when drive signal is applied, no less adding into the mix that El84s and 34s need less drive signal for a given power transfe.

You would get a far better mix of different harmonic overtones one the tubes start to clip if you ran 2 tubes out of a quad in Triode mode like Mesa did with there simil class outout stage, but then you still have the issue that the tube in Triode mode will need a bit more drive signal to reach clipping.

In my fooling around with EL84s and 6V6s in the same amp I found i had the best and widest dynamic range of clean tones and dirt if I set up the 84s to start clipping first with the 6V6s going into clipping once the 84s where 50% of the way to max square wave.
You can spend a ton of time messin with this type of stuff so in my humble opinion if your not going to be using a amp set up like this and pushing it hard enough to clip the output stage 75 % of the time your playing it then I see no real need to do such, but as I stated above the great dynamic range that amp of mine had has made me many many times want to set it up that way again!
Then again it on your dime and your time!