New AC 4ish build

[randalp3000]

Getting ready to start a new project. First build with a blank chassis, going to use a bigger one for the first then build another in a very small chassis.

Basically an AC 4 without the trem circuit using an EF86 preamp like the originals. I might end up doing switchable coupling caps.

Here's the schematic I whipped up, please let me know if you see anything that's not cool.

thanks
rp

[Reeltarded]

Where is... the rest of it?

[chief mushroom cloud]

cool idea, but that's going to hum a bit....you might want to put pi filter before the B+ to OT
definitely do the coupling cap switching

[overtone]

listen to the Chief about the power supply.

I am wondering why you have lowered the first stages of filtering and the CRC filter resistor down to 500R?

With the diodes you will have higher voltages than with the original EZ80, is that what you are going for?

If it was on my bench, I would play with the value of the EF86 screen resistor. You may find you prefer a 1M there, like the 1960 AC15 or AC30/4. Fiddling around with that Plate / Screen resistor combination of values (and the value of the screen bypass cap) can be fun and instructive if you have never done that.

Hope this helps a little.
Best, tony

[randalp3000]

thanks for the tips,
is this what you're talking about for the power supply? see below

yes I'm going for a higher voltage for a little more balls. Should I still raise the 500 ohm to a higher value? I came up with the power supply after looking at a bunch of different SE circuits including the mini Z. Also I have a bunch of 22uF caps from apexjr and I'm trying to use what I have on hand.

I was also thinking about the standard ac15, ef86 circuit but I'm curious to see how this circuit sounds and responds.


updated

[chief mushroom cloud]

change that 1k to 250 ohms 5W
the 500ohm might like to be 1k.....otherwise your B+ on the EF86 is going to be high...but try it and see where she lands

[randalp3000]

thanks chief, will do

here's the progress so far

[chief mushroom cloud]

here's another tip:
since the power supply and '84 Rk is ballpark..
tack these resistors in w/ long leads...don't dress them in. This way it's easy to swap values to fine tune the build. Once you have it dialed in, then take the resistors and dress them onto the tagstrip neatly. This goes for any values resistor or capacitors you might tweak.
Try to to dial in the EF86 B+ at ~275-300V

Just so you know, this amp will not have any serious grind w/o another gain stage. But w/ the right boost pedal..it'll be terrific.

[randalp3000]

Thanks again guys,

It lives, hope to get into it more tonight. Bias looks pretty good so far with a 200 ohm. Going to try the 1M on the ef86 and probably do a bright switch and a click control for the coupling cap. I had a big gig Sat night so not much progress.

[randalp3000]

So this is where it's at for now, installed click and bright switches. Sounds good but everyone's sleeping so I can't turn it up. I'm going to take it to work tomorrow so I can crank on it through a Z Wreck cab.

[iulker]

I built 3 versions of AC4 ... it's a great little amp!