Questions about Cornet Octal Hybrid

fishydan · « **on:** 20 May 2005, 12:50 am »

Hello-

I have decided to build my Cornet 2 as a hybrid, with the 6SN7 in place of the 12AU7. I have several questions for the experts-

1. Can I use a GZ34 S in place of the 5Y3GT?

2. Jim mentions changing the values of several resistors. Flocchini reported changing R220 and R221 to 1.2K, R218 to 510, and R223 to 1.1 ohms. Are these the values I should use?

3. Are there any other changes I need to make? I have already connected the octal socket in place of the 9 pin.

Thanks in advance. I appreciate the help.

Dan

rotcoddam · « **Reply #1 on:** 20 May 2005, 02:47 am »

I ran the stock cornet2 for a couple of months, then changed it to a hybrid. Excellent mod.

Here's what I did.

1. Install 1 octal socket in 12au7 spot.

a. install a wire from pin 1 to octal 2
b. install a wire from pin 2 to octal 1
c. install a wire from pin 3 to octal 3
d. install a wire from pin 4 or 5 to octal 7
e. install a wire from pin 6 to octal 5
f. install a wire from pin 7 to octal 4
g. install a wire from pin 8 to octal 6
h. install a wire from pin 9 to octal 8

2. Change r218 to 510 ohms 1watt. 2 places.

3. Change r220 and r221 to 1.2k 1watt. 2 places each.

4. Change r223 to 1 ohm 5watt. May need to be adjusted from .910 to 1.1 to get 6.2v heater voltage.

5. Plug in 6sn7. (Ratheon?)

Parts List

1. 1- octal socket
2. 2- 510ohm 1w r218
3. 4- 1.2k 1w r220, r221
4. 1- .910ohm to 1.1ohm 5w r223
5. 1- 6sn7 tube
6. misc wire, solder, etc.

Eric H · « **Reply #2 on:** 20 May 2005, 06:07 am »

As for the GZ34 - yes, they work great. I use them in both my cornet and clarinet. They will up your voltages ~10V, but mine were a bit low to begin with. One that you probably don't want is the 5U4...

flocchini · « **Reply #3 on:** 20 May 2005, 06:21 pm »

I have been really happy with my Octal Cornet2. Changes were per my previous posts. I am currently using Sylvania NOS and a Mullard GZ34. Great sound.

I also adjusted the 5W resistor to get 6.3V on the filament.

Bob

fishydan · « **Reply #4 on:** 20 May 2005, 11:22 pm »

Hello and thanks for all the info.

Now I'm wondering- I have tried to keep the various jumpers separate in my 9 pin to octal conversion. I thought it would be a good idea to not allow the jumpers to be in contact with each other, in oder to minimize the chance of hum. Is this a good idea, or am I being overly cautious?

Thanks, Dan