Hi,
I found three GM70 datasheet on the web, this on Image 1 seems incorrect on the tube pinage. On this GM70 datasheet PDF file(image 1) there is a pinout drawer totally wrong or Iam missing anything??
Image 2 show the same pinout drawer with zoom, Image 3 is a real GM70 pinage photo, it is visible there is some differences in pins positions and mainly in the thicker pin tradicionally reserved to the plate.
IF I identify correctly the tube elements in Image 4 and looking into the glass at tubes I have on hand, it show the four pins are connected as see on Image 5.
This Image 5 pinout is usual for GM70 graphite plate??
There is two pins connected to the grid, this is normal??
Thanks for any help, Gustavo
I found three GM70 datasheet on the web, this on Image 1 seems incorrect on the tube pinage. On this GM70 datasheet PDF file(image 1) there is a pinout drawer totally wrong or Iam missing anything??
An externally hosted image should be here but it was not working when we last tested it.
Image 2 show the same pinout drawer with zoom, Image 3 is a real GM70 pinage photo, it is visible there is some differences in pins positions and mainly in the thicker pin tradicionally reserved to the plate.
An externally hosted image should be here but it was not working when we last tested it.
IF I identify correctly the tube elements in Image 4 and looking into the glass at tubes I have on hand, it show the four pins are connected as see on Image 5.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
This Image 5 pinout is usual for GM70 graphite plate??
There is two pins connected to the grid, this is normal??
Thanks for any help, Gustavo
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I don't have a GM-70 to physically look at, but here is a datasheet in Russian that shows a base which matches your tube.
The drawing of the base on the datasheet you posted does not match your tube; the location of the large pin is different. Where did that datasheet come from?
Michael
The drawing of the base on the datasheet you posted does not match your tube; the location of the large pin is different. Where did that datasheet come from?
Michael
Attachments
I find this datasheet at Frank's Tube Datasheets http://www.shinjo.info/frank/sheets/084/g/GM70.pdf there is other PDF file in this site, that show this drawer you show, looks this is the correct.
Many thanks, Gustavo
Michael's drawing seems to be correct.
It's very easy to look into an actual GM70 and identify the pins on sight.
You'll find that the two pins closest together are the filament. One of those is thicker than the rest.
Then you'll see that of the remaining two pins, one is hooked up to the plate and the other is hooked up to one of the control grid support rods.
What I do is I put a GM70 loosely in a ceramic socket, then identify the pins in this way, and I write them on the bottom of the ceramic socket with a pencil. Makes it very easy while building the amplifier.
Kenneth
It's very easy to look into an actual GM70 and identify the pins on sight.
You'll find that the two pins closest together are the filament. One of those is thicker than the rest.
Then you'll see that of the remaining two pins, one is hooked up to the plate and the other is hooked up to one of the control grid support rods.
What I do is I put a GM70 loosely in a ceramic socket, then identify the pins in this way, and I write them on the bottom of the ceramic socket with a pencil. Makes it very easy while building the amplifier.
Kenneth
OH YESSS, now this is clear. Thanks alot Kenneth. Taking one more image from JacMusic, the four shorts pins in this image should be the cathode.
Looks to me the support rod that are connected receive the Bias.
Thanks for your help, Gustavo
An externally hosted image should be here but it was not working when we last tested it.
Yes. The 4 short rods are where the VVV shaped filament/cathode is held in place. You can still see some remnants of it in the photo. The three "tops" of the VVV are held in place with three springs at the top of the tube, as you can see in this photo:
http://www.positive-feedback.com/Issue9/images/845_closeup_top_down.jpg
Kenneth
http://www.positive-feedback.com/Issue9/images/845_closeup_top_down.jpg
Kenneth
OH GREAT!! Now we are reaching some place... Seeing a GM70 I have, really there is three wire upright inside the plate, that are held in place at the top ceramic disc as three springs. Thanks again,
Gustavo
An externally hosted image should be here but it was not working when we last tested it.
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For information to newbies tube fans like myself.
An externally hosted image should be here but it was not working when we last tested it.
The plate is a huge solid black graphite piece and the anode is a metal post+leads attached to the plate.
I really love to made myself a GM70 SET, but Iam a real dumbo in electronics, so I plan buy parts and have a GM70 SET custom made in some brazilian builder.
Unhapilly I was full surprised afew months ago when a local tube builder in my city flatly refused to made this SET monoblocks for me.http://www.schmaedecke.com.br/index.html
So now Iam considering order a custom SET in the U.S. because in North America there is various output transformers manufacturers.
Do you know IF the Silk(SAC Thailand) OPT is a good sound trafo(6.6Kohms primary)??
Gustavo
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It's the same thing, really. Americans say "plate", the rest of the world says "anode". When talking about tubes, it's one and the same thing. The metal post is just a mechanical support, and the leads are just an electrical connection from the graphite anode to the outside world.
Not all builders would feel comfortable doing such advanced projects, I guess. GM-70 and 6C33 are not really "easy" tubes to build something with.
I have no idea, I have two C-core SET OPTs from a maker in Holland but they're still waiting to be put into action (with GM70's of course).
Kenneth
Thankyou, the Link is: Automatic Electric Europe
Do you know what is the best sound option for a GM70 Set?? EI core, C core or Amorphous core??
Gustavo
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