5F4 build-wonky voltage w/Copper Caps

[Travst]

I've been working on a tweed Super build and started testing the completed amp prior to installing the tubes. Everything looked pretty fair with only a couple of voltages that were slightly out of whack in the preamp tubes.

My next step was to install the Weber Copper Cap in place of the 5U4G tube and test without any other tubes installed. I've never used a Copper Cap before, and chose it because the Ballentine PT doesn't have 5v leads. Referencing the attached Ceriatone layout, I have three wires running to the rectifier at pins 4, 6, and 8.

Prior to installing the cap, my voltage at pin 8 on the rectifier was 253v. After installing the cap, it jumps to over 400 and feeds that voltage down the line to the preamp tube sockets. I've researched the Copper Caps, but haven't found an answer as to how to tame the voltage or whether I've mis-wired something. I'd appreciate your thoughts on this. The attached voltage chart is from Ceriatone.

[Prairie Dawg]

That's not surprising. Once you have the electrolytics connected the voltage goes up. On one of my Champ builds the voltage before I hooked up the electrolytics measured about 100v less than what I ended up with.

[Zippy]

You don't get voltage drop across a resistor until it's flowing current - got to check operating voltages under load.

[rdjones]

Once again Ceria graces us with a layout that contains mistakes.
Don't follow the layout for wiring, follow a known correct (Fender) schematic.
The layout should be used as a general guide for physical planning only.

On this one -
Don't use a transformer bolt for the chassis ground.
Yes, Leo used transformer bolts for grounds, he also used a 2 prong cord. We've come quite a ways in terms of safety codes adherence, follow modern safety techniques.

The grid feeds for the 6L6s should be to the grids stoppers.
The layout shows them being bypassed.

rd

[Travst]

Thanks for the responses, that gives me some comfort level that things are normal. rd, I didn't use a transformer bolt for ground, I used a terminal strip for the CTs and a separate ground for the green wire at point E. Is that proper?

I did follow the Ceriatone layout with regard to the grid feeds, having not caught the difference from the Fender schematic. I appreciate your catching that error. Looking at the Fender schematic, it appears that the leads from the board should be attached to Pin 6 of each 6L6 rather than Pin 5. Is that correct?

Looks like I'll be good to go after making these changes.


*edit* Ceriatone has a newer version of the layout up, and it's been changed to have the leads attached to Pin 6.

[rdjones]

Thanks for the responses, that gives me some comfort level that things are normal. rd, I didn't use a transformer bolt for ground, I used a terminal strip for the CTs and a separate ground for the green wire at point E. Is that proper?

Yes, good choices.
I suppose it's OK to use a transformer bolt to anchor the star point, but ideally you want to minimize return current flow through the chassis.
The main earth ground should always have it's own secure attachment point close to the point of entry.
This is less of a concern when using an IEC connector than it is with an attached power cord, but is still good practice to follow.

I did follow the Ceriatone layout with regard to the grid feeds, having not caught the difference from the Fender schematic. I appreciate your catching that error. Looking at the Fender schematic, it appears that the leads from the board should be attached to Pin 6 of each 6L6 rather than Pin 5. Is that correct?

Right. There's no pin 6 on a 6L6 base so it's common in Fender and other designs to use it and pin 1 as a tie point instead of installing a terminal strip for grid stoppers or screen buffers.
Grid stoppers are most effective when placed as close as possible to the grid connection at the tube base.
I don't personally like to use pin 1 as a tie point because the original convention for octal sockets is for pin 1 to be a ground connection.
I just use pin 6 for the grid stopper, fly the screen resistor, and ground pin 1.
This opens up more tube swap possibilities.

Looks like I'll be good to go after making these changes.

*edit* Ceriatone has a newer version of the layout up, and it's been changed to have the leads attached to Pin 6.

I'm glad to see the updates on Ceria's diagram.
Since he's become a big player in the amp kit arena I feel that carries some responsibility to provide decent documentation.
I'll continue to call out any mistakes I find in any vendor's information.

reddog Steve

[Travst]

Thank goodness for these forums. It'd be impossible for me to learn if it were not for the contributors here and a few other key sites. Every project makes me a little bit better. I wish I could apprentice with someone for a bit and get a massive dose of schooling.

[Travst]

I finished this project last weekend except for fabricating some covers to fill the gaps in the cutout. My chassis came from Victoria and I got the cab in a trade, so the two weren't a perfect fit. The amp sounds great, particularly after Sam T. devised a quieter grounding scheme. Thanks again for all the help, I made all the suggested changes.

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[Phil_S]

My next step was to install the Weber Copper Cap...

Prior to installing the cap, my voltage at pin 8 on the rectifier was 253v. After installing the cap, it jumps to over 400...

I think you received the answer, that voltages should fall into line when you put the tubes in. If they don't I suggest contacting Weber. (I'm assuming "Copper Cap" is Weber's product.) It may take a few days, but you should get a reply. I belive Weber has it's own forum, too, where you can probably post for something this specific if you feel the need.

[Travst]

My next step was to install the Weber Copper Cap...

Prior to installing the cap, my voltage at pin 8 on the rectifier was 253v. After installing the cap, it jumps to over 400...

I think you received the answer, that voltages should fall into line when you put the tubes in. If they don't I suggest contacting Weber. (I'm assuming "Copper Cap" is Weber's product.) It may take a few days, but you should get a reply. I belive Weber has it's own forum, too, where you can probably post for something this specific if you feel the need.

Thanks Phil, the answers here got me squared away. As soon as the tubes were in, everything fell into place. I guess the lack of knowledge on my part seems a bit silly, but all I have is the forums and a couple of books on amps. The assistance from you guys has been invaluable. On the plus side, I haven't blown up anything or shocked myself (yet).