ECC99 push-pull build with JCM800 preamp - the JCM Eight Hundredths

[KevinOConnor]

Hi Guys

An EF-86 is a bi extreme and you wouldn't get much output.

Have fun

[PeanutNore]

Hi Guys

An EF-86 is a bi extreme and you wouldn't get much output.

Have fun

Yeah, mainly I just want to hear what an EF86 sounds like as a power tube without spending a bunch of time building something for what's probably going to be pretty underwhelming. If I end up cracking this thing open and rewiring anything it would probably be so that I could run a 6Н6П (6N6P) in place of the ECC99 - I think I would only have to change the heater wires.

[Zozobra]

A fun project for sure. I love the simplicity. Good job. I reckon the output is 400mW clean

It got me thinking. The self split can only ever do class A. Also with, of necessity, a small value of resistor in the cathodes it means the currents in the two halves are not equal. On paper I experimented with a constant current source in place of the 1.5K. This improved things a lot. If I also set the current to 19mA or so ( max ECC99 Pd) and changed to load impedance to 48K I could get 1.4W out. You could get 45k from your current transformer if you connected a 16 ohm speaker to the 8 ohms tap at the expense of a little loss on the low end. If you leave it at 22.5K the power out is 900mW. If you want to play this is what I used for a current source:

[ATTACH=CONFIG]41324[/ATTACH]

The transistors are nothing special, 40V will be fine, HFE>50. Q1 does dissipate 350mW so pick something suitable. The BC337 shown is 625mW at Tambient = 25C. A bit beefier wouldn't be a bad thing.

I missed this the first time around. Any idea on what kind of impact this might have on the tone over cathode biasing, other than increased output? I'm considering building something like this as a recording amp as at 0.9W output I can make a reactive dummy load without the expense of air-core inductors. I have a 2U rack chassis and a suitable toroidal PT sat doing nothing so I should probably put them to good use and I do like the idea of the Fryette GP/DI, just not what it'd cost to import one since the exchange rate took a huge dump.