My G7 Build Thread

Hi everyone. I've got a pair of g7's in the works. I built most of the bodies in the cold of last winter. They are very close to being finished I hope. I'll post some pics I took along the way. I'm still needing a few things done but I'll post about that later after the pics....

2" copper tube from menards.

2" fender washer from menards. I used a step bit on the drill press to widen the hole. Ten a small triangle file to accept the tab.

I used 1/4" aluminum square tubing for the structure. Had to order this online from a hobby parts company.

The pair together.

Soldering...

This is how I did the tube pcb. I glued it in and soldered cutoffs from the resisters. Seems really solid.

Where we are currently.

And the power supply. Which is making me scratch my head.

So I still haven't ordered grille material. I'll order from this page.

http://www.mcmaster.com/#brass-mesh/=s5embe

Wondering if anyone has any input on mesh size and opening size?

I also am still looking for a way to have a set screw that holds the mic inside of the body. Maybe someone has a link for a really small female part that would mount at the bottom and have a set screw come through the body. I'm having a hard time finding this because I don't know what it's called?

Trying to finish my power supply without having my mic finished yet so wondering if this is working. before hooking up my transformers to the board i paralleled the seconaries of each transformer and connected them together and was getting 12.8 vac between them. Then i ran the 2nd transformer primary in series and measured 140vac on it output.  After soldering these to the board i measure 6.6vac between the two 9v solder points and 28vac between the two 120v solder points. I also measured between ground and pin 2 and get 4.2 vdc. It also seems that the first transformer is getting pretty hot.

Any advise on what to look for?

re-check the transformer connections, do you have a variac or stepdown /isolation transformer?

nice project

No I don't have a variac... I'll recheck the power supply today.

Thanks to comodocomplex for the part numbers. I just ordered this mounting bracket...
Digikey part number..
612K-ND

And the 14x14 mesh from McMaster Carr.

try powering them (the power supply p.t.s) from a 12vac winding (in place of 120) to see if the measured voltage ratios make sense. doing this instead of directly to the mains will help avoid smoking any transformers.

ps what size fuse were you using?

Hey man
what a nice build 
what tube did you put in your mics?
can't wait to see the project complet

cheers

C.

Hello,
Nice Build.Hope You get Your Powersupply issues solved.
Just a few Thoughts.
If you have 160 Volts for the B+ Voltage, this results in 80 Volts Polarisationvoltage. If You use a Capsule that can take only 60 Volts , what are most Capsules excluding the original AKG and the Tim Campell TC 12 , the Diagram might get pulled into the Backplate. This happend to me with a Rk12 Type Capsule. Have a look here how to solve this Problem :
http://groupdiy.com/index.php?topic=25597.0
or this:
http://groupdiy.com/index.php?topic=51320.0
I have 2 double Powersupplys for my 2 Pairs of G7 s. With one Pair, I did the mod from the second Link, the other Powersupply give me 130 Volt B+ Voltage ,65 Volt for the Backplate, and 0/65/130 Volt polarisation Voltage for the rear Membran. This works also very good. The Sound of the different Pairs are not compareable because they have very different Capsules (Rk 12,Dale M7 ) and different Outputtrannys ( the beautifull Haufe that silentart offers in his Shop at the Whitemarket for the Rk12 and a vintage UTC O8 wired for 10:1 (15k:150 Ohm ) for the M7 equiped G7) Both Pairs sound fantastic but different.
I also bridged the 10kOhm Resistor in the B+ Line for the Polarisationvoltagestring. This gives You a better, more balanced Figure of 8 Pattern because without doing this Your Rear and Front Diagramms have little different Outputs,as they sit at different Voltages.
Do You have a spare,cheaper Ef 86 that You can install during testing? It would be a pitty if You blow Your beautifull Telefunken Silvershield .
Your Cathodebypasscap looks very small and cheap. I used Panasonic FC 220uf 35v.
I also enlarged the smoothingcondensers for the Heatersupply in the Powersupply to 22k uF and installed a 100 n Filmcap at the 7 pole Xlr for a Hf Filtering.
Condenser are cheap ourdays and I think its good to have a big Reservoir for the Heatercurrent.
Greetings and happy building.
Lothar

Hey thanks for the help guys. I'm going to try to get back to the power supply this weekend if I can find the time. Had the day off today so I got quite a bit done. I'll post pics.

Peluso CEk-12 mounted!

Just gotta finish the top grille!