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Oliver Acoustic Research AR-94 specifications
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Description

Paul Hatton's website (December 2000): The amplifier was built on a homemade brass chassis. The top plate is a piece of 3mm thick brass which in retrosect is far too thick to work with the hand tools I have available.

It is quite difficult to find ready made chassis these days so I usually make them myself. I use sheet metal for the top bottom and sides and 1/2" angle to join the corners together.

I used brass sheet and angle here for cosmetic reasons but for most of my ham radio tube proects I use aluminium. Thin Aluminium sheet is very easy to work with hand tools and can be easily and cleanly cut by scoring both sides with a sharp Stanley knife and "waggling" the two halves. The sheet breaks apart with a nice clean join. For a very quick chassis the aluminium panels can be joined with a hand rivet gun. It gives a slightly industrial look to the chassis but is very simple.

I only have hand power tools available and the holes for the transformers were cut in the brass top plate using a hand held jigsaw with fine toothed blade. The worst job was amking the holes for the valve holders. The 3mm brass sheet used here is far too thick to use a Q-Max hole punch on and so I first made the holes with the largest drill bit that will fit in my electric hand drill and then enlarged them using a hand reamer. No fun!

The chassis is very sturdy and doesn't look too bad from above. I should have spent more time making the corners of the angles better, but in practice this can't be seen normally. The bottom of the amplifier will be secured either by soldering brass nuts to the angle or possibly by tapping the fixing holes

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Building

Current status

Conclusion

I had initial hum problems but these have been cured by paying more attention to the grounding. The amp is in use mainly driving a pair of Chartwell 15R LS3/5as although I also have a pair of LS5/9s which I have used the amp with.. It was immediately apparent that this amplifier sounds much better than my other two, a Quad 405/II and a homebrew MOSFET power amplifier. Without doubt this is the nicest sound I have heard from the LS3/5as in the past 25 years.

The next project? I'm scrounging parts for something a bit more powerful. I have four 6146Bs in the junk box......

Paul Hatton. (July 2000)