Radiocraftsmen RC-2

[Edo]

Hello, I am new to this site. Back in 1956 i built a clone of the RC-2. I am in the process of building two more. I think I will replace the 6J5 with a 12AX7 or 12AT7. Does anyone have any comments on this subject?

 

[thorpej]

Well, a 6J5 is basically 1/2 of a 6SN7, right? So, if your intent was to use the smaller-envelope tubes, then use a 6CG7 / 6FQ7 instead (because they're electrically equivalent to 6SN7). Or if you're just looking to reduce parts count, use an octal socket and a 6SN7 (which is just a lovely tube).

If you were to use a 12AX7 or a 12AT7, you'd have to make changes to the surrounding circuit, and those tubes might not be very suitable for the purpose the 6J5 served in the original.

 

[Palustris]

As is asserted above, you would need to draw new load lines for a different tube and re-compute the cathode resistor and plate resistor. Further, the entire feedback network would have to be re-engineered if you change the 6J5 to a 12AX7 or 12AT7.

 

[cademan]

Since the 6J5 is basically half of a 6SN7, then you could use 1/2 of a 12AU7 tube.

 

[Steve O]

Since the 6J5 is basically half of a 6SN7, then you could use 1/2 of a 12AU7 tube.

Or an entire 6C4.

 

[Selmerdave]

Check out a few other threads there are here on the topic. Many people (myself included) eliminate the 6J5 stage altogether, with the 6J5 the input sensitivity is .75V for full power, much higher than necessary and the result is higher noise with no other benefit. What are you using for iron? Which schematic did you use?

 

[cademan]

Or an entire 6C4.

Yes, I forgot about the 6C4.

 

[Edo]

Check out a few other threads there are here on the topic. Many people (myself included) eliminate the 6J5 stage altogether, with the 6J5 the input sensitivity is .75V for full power, much higher than necessary and the result is higher noise with no other benefit. What are you using for iron? Which schematic did you use?

I used the Sams Set 176 Folder 8. I am using an bridge instead of 5U4. Sorry i have to go now. Be back tonight.

 

[Selmerdave]

Cool, good to know, thanks. I'm using the other one (paraphase), I'll probably try that one too. I wonder if anyone has tried both that could report the differences...probably not as they're not really common.

 

[Edo]

Check out a few other threads there are here on the topic. Many people (myself included) eliminate the 6J5 stage altogether, with the 6J5 the input sensitivity is .75V for full power, much higher than necessary and the result is higher noise with no other benefit. What are you using for iron? Which schematic did you use?

Musical Power Supplies Inc. OPT= OT20PP PT= PT285M. Will use two 6L6 PP. I want too add volume and tone controls. I am not sure of the circuit changes I will make.

 

[Edo]

Thanks much for all your comments. I will let you know how this works out. I received more parts today, almost ready too start building.
I am planing to build two amps on one chassis. Two PT's, OT, choke. Now I am trying to figure out the layout of the Iron and tubes.
Wish me luck.

 

[Selmerdave]

Sounds good, good luck with it and report back!

 

[Edo]

Having problems with the layout orientation of the transformers. I am using two PT's, two chokes and two OT's.View attachment 717383
(1) I usually place the OT's on the opposite side of the PT's as shown but how do you orientate the chokes?
(2) I know most people locate the power tubes next to the PT's too keep the B+ wires short and the #1,2,3 in a row. I have very little space on my chassis to locate any of the parts.
(3) Does anyone have any ideas on the location of the components?
(4) Would you keep the power supplies separate or parallel the PT's and use one power supply for both amps?
The amps I built in the past were on separate chassis and no choke. This one will have two amps on one chassis. Sorry about my fancy drawing of the layout.
Any of your comments will be greatly appreciated.

 

[Edo]

Yes, I forgot about the 6C4.

Your icon looks like my cat Coco.

 

[Edo]

Well, a 6J5 is basically 1/2 of a 6SN7, right? So, if your intent was to use the smaller-envelope tubes, then use a 6CG7 / 6FQ7 instead (because they're electrically equivalent to 6SN7). Or if you're just looking to reduce parts count, use an octal socket and a 6SN7 (which is just a lovely tube).

If you were to use a 12AX7 or a 12AT7, you'd have to make changes to the surrounding circuit, and those tubes might not be very suitable for the purpose the 6J5 served in the original.

I meant to say a 12AU7.

 

[Selmerdave]

My only comment is keep the power transformers separate, therein lies the benefit of having two.

 

[Edo]

What about the orientation of the PT and OT's? I have them shown my drawing the way I think they should be mounted. If I am wrong please tell me.

 

[Selmerdave]

I don't think I'm knowledgeable enough in that area to be giving advice, but I think generally I've seen similar designs that have left and right channels parallel for what that's worth.

 

[Edo]

I don't think I'm knowledgeable enough in that area to be giving advice, but I think generally I've seen similar designs that have left and right channels parallel for what that's worth.

Well maybe someone else has some ideas.I am new to this BB and am looking for some conversation and learning something. Thanks for your comment.

 

[Edo]

Since the 6J5 is basically half of a 6SN7, then you could use 1/2 of a 12AU7 tube.

I am looking at using a 12AU7 and am working on the circuit. I want to use the AMP for Computer or TV audio input. My schematics has no volume or tone controls. I want to add the circuitry for them. Work is in progress. I have Dialysis three days a week and half sick the rest of the time so I am slow working on this project.