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Author Topic: National GA920P Schematic  (Read 8828 times)

galaxiex

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Re: National GA920P Schematic
« Reply #45 on: December 17, 2017, 09:49:45 AM »

1/2? Thanks.  Was told the transistors went bad, they were replaced but, resistors, no.and yes, he was lazy... Haven't gone in myself as without a schematic, I don't touch...or help. I will rectify both the resistors and shoddy wiring, will report back. Oh, and the amp was only used with the cabinet it came with, a 2x12...haven't measured cabinet Z yet, so...It does look like the original cabinet. Will post more pics in the morning,Thanks.<

Likely won't ever find a schematic, and that means you will have to draw it yourself.

The main board doesn't look very complicated, should be fairly easy.

What I do...

Take good pics of where everything hooks up to the board AND hand draw a picture of where every wire attaches.
Label accordingly. The more detailed you make this, the less chance for mistakes when re-installing the board.

Remove the board from the amp and scan the copper side.
Import the scan into a graphics program (I use paint.net).
Flip the image so you have a component side orientation, as if an X-ray from the top component side.
Print that, and hand draw the parts right on the picture.
Now you have a layout diagram.

Draw schematic from that.
I use Express PCB which is a free program and comes with Express SCH schematic drawing program.
You could also draw it by hand.
Several of my first attempts at drawing a schematic I did by hand.

HTH
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lotus1

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Re: National GA920P Schematic
« Reply #46 on: December 17, 2017, 11:00:15 AM »

Very cool ideas...Thanks..will attempt when I can get some time..Just effected the "repair" so, fingers crossed it'll work. discovered why the funky red wire attachment..the solder pad had lifted when the original repair was done. fixed that a little better. get to try it out a bit later. Than ks all, cool place here. Next up is my peavey session 400 which ate the speaker voice coil. Putting out something ugly. had a wind shear go thru woods around studio took power out while amp was on..we see.
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lotus1

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Re: National GA920P Schematic
« Reply #47 on: December 20, 2017, 09:36:49 AM »

Effected repairs, Had to use a 1ohm resistor instead of .5...It's alive!! Workd again and that very cool sound is being heard again, Once again, Thanks for all. Will try to post pics soon.M
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galaxiex

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Re: National GA920P Schematic
« Reply #48 on: December 20, 2017, 09:57:12 PM »

Effected repairs, Had to use a 1ohm resistor instead of .5...It's alive!! Workd again and that very cool sound is being heard again, Once again, Thanks for all. Will try to post pics soon.M

Good to hear you got it working!
Looking forward to the pics.  :)
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lotus1

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Re: National GA920P Schematic
« Reply #49 on: December 22, 2017, 05:00:34 PM »

Pics.
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galaxiex

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Re: National GA920P Schematic
« Reply #50 on: December 22, 2017, 07:41:55 PM »

Cool looking amp!  8)

Are those 12" speakers?
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lotus1

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Re: National GA920P Schematic
« Reply #51 on: December 22, 2017, 07:46:33 PM »

Yes, 12" ceramic magnet, no names...sound pretty good tho. Kind of a Gilmour sound...That clear but "warm" thing.
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lapsteelman

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Re: National GA920P Schematic
« Reply #52 on: January 13, 2018, 11:42:55 PM »

Haven't posted in awhile, just wanted to chime in and say a guitar player I was playing with got his hands on one of these.. I think he put a couple different speakers in the cabinet... but it sounded fantastic! REALLY great surf tone..
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galaxiex

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Re: National GA920P Schematic
« Reply #53 on: January 14, 2018, 06:35:18 PM »

Haven't posted in awhile, just wanted to chime in and say a guitar player I was playing with got his hands on one of these.. I think he put a couple different speakers in the cabinet... but it sounded fantastic! REALLY great surf tone..

Nice!
Ya, they are cool amps.
I have no doubt it sounds better with different speakers.  :)

I started a project custom cabinet for mine and I need to get back at it.
Life stuff got in the way....  ;)
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