GRO or not ?

Maybe someone can help you date your Orange Amplifier?

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GRO or not ?

Post by OliverKing » Thu Jul 23, 2009 4:24 pm

Hi folks,

i bought this amp written GRO100, but it does not seem to be a GRO !?
Serial No. 876

Am i right ?

By the way does anybody knows when the speaker connection have changed from 7.5/15 Ohm to 8/16 Ohm ?




Andy H.
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Post by Andy H. » Thu Jul 23, 2009 4:52 pm

Odd one. I think the chassis could well be an older GRO which has had a new faceplate and possibly headsleeve.
I'd have expected a GRO to have the 'pix only' faceplate, but that has 'pics and text'.

See here:
Orange Amps Field Guide:

Not sure straight off when they rounded the impedances up to 4/8/16, but you can check there too.

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Post by OliverKing » Thu Jul 23, 2009 9:59 pm

Thank you, this was very helpful.

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Re: GRO or not ?

Post by fiveightandten » Fri Oct 23, 2009 4:01 am

I have GRO #559 and the amp has a pix-only plexi face plate. The faceplate on this amp looks like a mid-late 70s unit that was likely thrown on there after the fact.

Some pictures of the inside of the chassis would tell the story a bit better, as the GRO circuit is unique to that amp.

Also, looks like the bell covers for the transformers were removed and painted. I'd venture a guess that someone nursed this one back to health from a lesser state, as evident from the replaced faceplate, original GRO knobs transferred over, painted bell covers (likely a rust fix from looking at the transformer tops) etc.

I believe they switched over to the "4, 8, 16" impedance markings in late 1972. The GRO would've been made in late '71 or early '72 based on the model and the S/N, and that faceplate is likely a post '74 piece. Some somewhere between '74 and '78.

'71 GRO100 || '96 OR-80 || AD30 || '64 AC-50 || AC-30TBX || Hiwatt DR504 || HI-TONE HT30
LP Standard || LP Studio || LP Custom Lite || Ric 620 || Ric 360 || MIA Tele || SG 61 RI

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Re: GRO or not ?

Post by Rally Car » Sat Oct 31, 2009 4:51 am

That is a Matamp made mid 70's GRO100 ...... You can tell its a Matamp made amp as it has the black transformers and the serial number written on the caps and transformers..... Matamp made some amps for Orange along the years.... The serial numbers on these amps follow the Matamp serial number system.... If you email Matamp at" onclick=";return false; they can give you the exact date of manufacture as they kept a record of serial numbers...

Cool amp!

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