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National GA920P Schematic

Started by galaxiex, September 13, 2015, 12:33:41 PM

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clintrubber

Aha, that auction just finished, 8 bids, winning bid US $57,66

Perhaps better not using mine as a donor-chassis/enclosure ;-)


galaxiex

Ahh yes... I was also watching that listing.
Just curious to see what it sold for.

I already have two so I don't need another one.  ;)
If it ain't broke I'll fix it until it is.

clintrubber

Quote from: galaxiex on November 02, 2017, 07:34:00 PM
Just curious to see what it sold for.

Same here, it didn't do too bad I guess.

OK, FWIW, a few quick and low-qual pics for now, this is mine with the 'blue left front', and the reverb tank right behind the front panel.

Bye



galaxiex

Thanks for the pics.  :)

Interesting layout compared to the others.

Can you do a overall shot that shows the whole chassis.
Thanks!
If it ain't broke I'll fix it until it is.

clintrubber

Quote from: galaxiex on November 05, 2017, 07:30:42 PM
Interesting layout compared to the others.

All those iterations are a bit puzzling/amusing! :-)  ... why ?!  8)

QuoteCan you do a overall shot that shows the whole chassis.

Here we go, 3 more pics, have a good weekend!

clintrubber

BTW, imho 5 Fender knobs look way better on this little amp than the bit smallish originals... just personal preference

galaxiex

Thanks for the pics!   :tu:

Looks like the reverb tank is "upside down" compared to both of the other ones.

I agree, all those iterations are a bit puzzling/amusing! 

Why? Who knows.   8) Different factory, different production run etc.

I too like the look of Fender knobs, but on these amps my personal preference is for the original knobs.
To each his own.  :)

Thanks again for sharing!  :tu:
If it ain't broke I'll fix it until it is.

lotus1

Hello, I just discovered this forum and thread. Very cool. Have a question tho. I have a national GA 960P amplifier.I am in need of a schematic or someone who has one as I have 2 resistors that need replacing but, have burned up to the point I can't read values. If anyone has one of this model, would very much appreciate any help. It uses 2SD428 output transistors. Thanks all.Mario

Jazz P Bass

#38
It may help if you describe where the resistors go.

What points do they attach to?
Resistors burn up when another part of the circuit demands eccess current.

DrGonz78

"A person who never made a mistake never tried anything new." -Albert Einstein

Jazz P Bass

#40
Wow!

Those two schematics are totally different.

As the OP is searching for a schematic that uses 2SD428 (TO3 mount) the schematics may or may not be of help.

Maybe the Gibson G30 is closer.

lotus1

Quote from: Jazz P Bass on December 16, 2017, 02:31:02 PM
It may help if you describe where the resistors go.

What points do they attach to?
Resistors burn up when another part of the circuit demands eccess current.
Yes, I understand, Was looking for the schematic but, Here's a couple of pics. It's the red ones connected to the transistor itself. One has the red wird connected directly, not sure why that is. Thanks for the replies, really like this amp, would like to get it running again. Mario

phatt

Those resistors will most likely be half an Ohm. (OR47)
Most likely reason for them burning up is someone plugging in an extra speaker which puts more current demand on the circuit.
These type of power circuits are basic in design and don't handle low Z speaker loads well.
re the red wire Q.   A; who ever fixed it last was lazy. :trouble

Replace those resistors and use the light bulb limiter (Instructions at top of this forum)

Phil.

lotus1

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.<