NFB arrangement on 69 ORST (50w)

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LD50
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Joined: Thu May 19, 2016 8:35 pm

NFB arrangement on 69 ORST (50w)

Post by LD50 » Fri Sep 15, 2017 9:29 am

I apologise to those who've seen this on VAF.
I have been analysing and blueprinting one of these.
It is very similar to the matamp 2000 aluminium chassis amps I have seen (nice reference on Chambonino web site) except for ss rectifier and transformers.
I am puzzled as I see no negative feedback on this amp. Pics of similar amp on the Field Guide.
The GRO and OR100 amps are quite different.
v2a cathode has 1k2 bypassed with a 47uf electrolytic with a 180R to ground (i.e. Partial bypass). The boost is separate.
Anyone know what I am missing ?

fiveightandten
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Re: NFB arrangement on 69 ORST (50w)

Post by fiveightandten » Tue Sep 19, 2017 10:49 pm

I don't own an ORST, but going from the pictures on the Orange amp field guide, it doesn't appear to have a NFB loop. The only wire I see coming from the OT secondary is a black wire that appears to be the ground connection.

The GRO has a presence knob, and the NFB to feed it. But it barely does anything.

The Matamp 2000 also does not appear to have a NFB loop, as per these photos:
http://www.chambonino.com/work/matamp/mat2.html

-Nick
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LD50
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Posts: 13
Joined: Thu May 19, 2016 8:35 pm

Re: NFB arrangement on 69 ORST (50w)

Post by LD50 » Thu Sep 21, 2017 2:46 pm

Thanks Nick

That was my conclusion, but just a bit surprised. Casting around I also discovered that the early Ormat 200 did not have one either.

I have just about finished. Post cap reform getting healthy voltages of 515 on plates without tubes, fingers crossed!

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