DIY Cornet 2 Hybrid

[MrEd]

I have had 2 of Jim Hagerman's Cornet phono preamps.
The first version and later the Cornet 2, which I lost to wild fire in 2011 that wiped out the neighborhood I lived in.

As the postal tracking label shows this project has taken a back seat on my audio journey till now.
In my opinion the Cornet 2 is one of the best phono preamps out there for bang per buck. The hybrid version substitutes a 6SN7 for the 12AU7 output tube.
Jim Hagerman has written that this configuration is what he considered the best vs. the 9 pin and all octal version.

 

[Fran604g]

I have had 2 of Jim Hagerman's Cirnet phono preamps.
The first version and later the Cornet 2, which I lost to wild fire in 2011 that wiped out the neighborhood I lived in.
View attachment 76229
As the postal tracking label shows this project has taken a back seat on my audio journey till now.
In my opinion the Cornet 2 is one of the best phono preamps out there for bang per buck. The hybrid version substitutes a 6SN7 for the 12AU7 output tube.
Jim Hagerman has written that this configuration is what he considered the best vs. the 9 pin and all octal version.
View attachment 76231

I'd sort of forgotten all about Cornet preamps. I didn't think they were still available but checking the Haggerman website I see they still sell the original version kit. Looks like a fun project Mr.Ed!

 

[MrEd]

Lay out on a piece of aluminum that will be folded to form the top , front and back panels.
The sides will be wood.

 

[MrEd]

I made holes today

The pcb is designed for three 9 pins and one octal.
The crux of the biscuit is adapting the 6SN7 octal socket to the board.
I decided to make a little sub plate with the tube sockets and then wire them to the board.
The slots on the sides are to vent the power supply resistors. I will mount these on the top of the pc board.

 

[Wntrmute2]

Still enjoying your Millett phono?

 

[MrEd]

Still enjoying your Millett phono?

Yes
But you know how this sickness works right ? 🙂

 

[MrEd]

I got a big box from Mouser this week.
After sorting and checking against the BOM I started populating the circuit board.
Pretty mundane stuff here.

 

[MrEd]

After deciding to change the power supply caps from electrolytic mounted on the board to Wima DC links, I needed a bigger chassis plate....

I can form the ends of this in a brake tomorrow at work and move forward.

 

[MrEd]

A normal person would most likely buy an adapter for the 6SN7 but I didn't want the tube towering over the others. I thought this would look cleaner.
But it has been a bit of a pia.

My idea was that if I mount the sockets directly to the chassis it makes removing the board for any changes or fixes difficult.
I made a plate that holds the tube sockets and it it held flush to the under side of the chassis. It comes out with the circuit board.
Wiring the octal to the 9 pin space on the board was a challenge.



To be continued.... 😊

 

[MrEd]

Wima DC link caps

I used these screws type terminals on the board to facilitate board removal and to experiment with some GE oil caps also.

 

[Salectric]

The Cornet is still a really fine phono preamp. I have a Cornet 2 in the storage room and pull it out from time to time. Mine uses the 9-pin CF. I hadn’t heard about Jim recommending an octal for just the CF but it makes sense. The 12ax7 has a clarity and focus that I don’t hear in the 6sl7.

 

[MrEd]

I did end up buying the RTX caps for the eq circuit and also for the output caps.
They look a little large but fit the board.
I wanted to use a Miflex for output but with the ps caps I was running out of space off the board.

 

[Salectric]

I mounted a terminal strip on each side of the Cornet with short jumper wires to the coupling cap holes on the circuit board. The coupling caps are soldered to the terminal strip, not the board. This way I can swap coupling caps without disturbing the board.

I also didn’t like the idea of having the rectifier tube mounted on the circuit board so I used a chassis-mount tube socket with short jumpers to the circuit board.

Despite my prejudice against circuit boards generally, I have to admit Jim’s board is an excellent design. The ground plane on the board is a big factor in the extremely low noise floor for the Cornet. It’s easily the quietest 12ax7 phono I have used.

 

[MrEd]

Agreed, the board is well made and rugged makes component swapping less worrisome .