• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Grounded Grid Preamp Project And Possible Group PCB Buy

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#63
Luke said:
Seems like an expensive power supply to build.
Would need twice the inductors transformers and caps. All these parts are quite spendy.
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One of the things that drew me to the GG was the low cost of the transformers. The 170 mA isolation transformers that are commonly available around here for $1-5 CAD are way overkill... the big cost so far has been the Solen power supply caps (~$60 CAD). Except for the zeners & probably some of the big Rs the rest is all out of the junk box. I'll probably end up using 12BH7s in it.

dave
 
#64
You're right Dave! The GG LS is super easy to build and a very inexpensice project thanks to those inexpensive isolation trannys. There are folks that owned preamps costimg well into in the thousands that got rid of them after using the GG. From my experience the zener regulated supply is as quiet or possibly quieter than a supply built with expensive chokes.

Mark
 
#66
Mark A. Gulbrandsen said:
I am more on the side of lets go ahead and do the project anyway ...
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Mark,

I wrote our beloved scarlet rodent summarizing the work I have already done on the GG board and the copyright-related questions I have. Since this is my first board using Eagle, I could certainly use his advice on giving it that professional touch that the KSA-50 boards have. Once he gets back to me we may be able to start moving quickly towards the completion of the boards, be it the original version, the 6SN7 based, or something in between. It seems as if this thread is finally gaining momentum, and I would like to keep it going.
 
#68
If I understand the concept of using the isolation transformers correct then this is only possible with countries with 120V primaries when using the original supply or am I missing something? Please enlighten me if there is an advantage using the zener regulated and voltage doubler supply used in the standard supply over the choke supply used in the wyetech 6sn7 grounded grid? About making the PCB are you also considering making a supply board?

I am looking forward seeing how this project will develop especially the 6sn7 version.

Martin
 
#69
The original power supply uses voltage doublers and Zener diodes for both 200V and -200V. For those living in areas where the voltage is 220V-240V, use just a regular full wave rectifying circuit after the isolation transformer followed by the Zener diodes.
 
#71
pinkmouse said:
Yep, and they all seem to be slightly different in radius/pin size etc... 🙂
Good idea. Do you know what the socket bases are perchance, or will they vary with the selected valve?
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The ones Bas used for the Aikido PSU were 26mm dia. I bought mine from diyclub.biz at $2.50 each.
I'd much rather have the sockets fit the board than have the sockets wired to the board. That defeats the pourpose of a board in my oppinion.

cheers
Svein
 
#72
Svein,

The board could be made to accomodate sockets but as of yet we have to decide which valve to utilize. Another version of the board would have solder pads along one length corresponding to socket pin numbers so that the board could be wired into any type of socket. This type of board would certainly make sense for a group buy in that it could be made into several versions of the GG by utilizing just one board and changing parts values to suit any valve you want to use. IMHO tjhis type of board makes the most sense for this type of project to keep it completely flexible.

Mark
 
#73
Steve @ Apex.jr sells tubes and sockets inexpensively. He also has most of the other parts required for building "stuff".

Most notably is the teflon isulated wire. A joy to work with since the insulation doesn't melt/ creep!

But if we can get a list of required parts Steve may be able to put a "kit" together from the parts he can supply, such as, tube, socket, wire, fuse holder, fuse, IEC input(he has nice filtered ones cheap), pwr switches, RCA sockets, and other stuff required to build one.

I'm not advocating Steve, I just find more projects are completed if everything is readily available from just one or two sources.
 
#76
After giving this alot of thought, reading the Akaido articles and comparing it to the GG schematics I am going to stick with the 6SN7 version of the GG preamp. This is mainly because it doesn't look as though the Akaido is capable of driving low impedance amp inputs but if I'm wrong then someone please correct me. I believe the 6SN7 GG will easily drive a 600 to 1000 ohm load.

Mark
 
#78
Troy, that sounds like a reasonable suggestion. If one of my US collaborators can get hold of one of the appropriate sockets to measure then we are onto a winner as far as I can see!

As for the option of using other valves, I'm sure we can build a little bit of flexibilty into the PCB to allow other versions to be constructed.
 
#80
Would this be a first good tube project?
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Absolutely. But you will need to treat this project with respect as it does contain lethal DC voltages!!


Today I went to the tube guy and picked up 3 12SN7's and 3 6SN7's NOS tubes and some cool Ratheon CK series minature tubes that are also NOS. The CK's are for a future project thouugh.

So the project begins..... I will gather more parts tommrrow. I plan on just using my trusty Eico 450 volt variable bench supply for doing these tests. It will supply the B+ and filament voltage as well.

Mark
 
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