Help check my schematic design

[thom_rees]

Hi guys I was hoping to get some advice on this schematic I've drawn up and want to build, I've built several amps from standard schematics and designs and would like to try and put something together from scratch, so this is my first attempt. It is pretty much just a combination of a few amps that I like and would appreciate any help or advice.

I'm going to start drawing up a layout to go with it when I get sometime but until then what does every one think.

[Alf]

I reckon you like Vox a lot ?

In the 2nd 12ax7 stage with 100 K plate resistor I would make the cathode resistor small like a 2k2 and the cap going to the PI I would also make a little smaller value like 47 n or 22 n .
And in the first half of the 2nd 12ax7 you a 100 k resisitor going to ground you could tweak this to get the right amount of signal into the next stage.

Alf

[Tiago]

Hi thom,
The things that I will point out is just my opinion, not an attempt to make your work look bad. And by the way, great work.
The things that I would do:
-Increase the cathode resistance of the output stage. Its safer starting with a high value resistance and then lowering it to the optium spot.
-Increase the screen grid resistors, at least to 270R or maybe 470R. Later it can be lowered if appears to be safe after measurements.
-I would directly couple the 2nd half of the 1st 12ax7 to the 1st hald of the 2nd 12ax7, no cap or 100K resistor in there. Thats because the way it is connected the cathode follower has low headroom, and the signal swing is high. If you couple it directly, cathode will sit at a much higher voltage leaving more headroom. Ideally I would be used a voltage divider to bias the cathode follower at 50Volt or so, but it would require to much circuitry for such a little thing, and the simplicity here really shines.
Also if it is to keep like it is, at least increase the value of the 100K resistor because it will stress a lot that 2nd half of the 1st 12ax7 and would add a 100K grid stopper.
-I would use a higher grid stopper in the grid of the 2nd half of the 1st 12ax7, instead of 820R I would use at least 100K.

As for the EF86 I can't give you any advice cause I've never worked with one.

I wrote a lot of things, but don't worry, most of them are picky little things and this amp will sound great anyway...at least it sounds in paper!!

Regards.

[thom_rees]

Yeah I like Vox, I also like alot of the boutique amps that started with a vox and mutated into there own great amps.

Thanks for the positive critic so far guys, I'm getting more and more excited about building this amp.

I would love any more ideas

[Enzo]

Hi Thom, welcome. The schematic is clear and easily read. May I suggest when posting a schematic for discussion, add part numbers. It is so much easier to refer to C6 and R17 than to explain what a part is connected to at either end.

Not really complaining, I just see all those Joe Piazza redraws of vintage amp diagrams where he always omits the part numbers and it drives me nuts.

[thom_rees]

No worries I'll go through and add some part no.

I will fix all my symbols at some point so it does it automatic