Date   : Tue, 26 Oct 2010 15:52:25 +0100
From   : jumbos.bazzar@... (Mark Haysman)
Subject: Reversing the Tube ULA (destructively)

----- Original Message ----- 
From: "Pete Turnbull" <pete@...>

> The original Tube ULA was made by Ferranti (part no 201,605).  The
> second version is an AMD chip (2201,266) which isn't an exact
> replacement, nor is it pin-compatible.  It's a CMOS device and was
> introduced when Ferranti ULAs became unavailable (to Acorn; they still
> had spares), in 1987.  The third device is a daughterboard (0359,400)
> which has one of the AMD chips, three transistors, and about 10
> resistors, and is called the Bipolar Tube Emulator PCB.  It was used as
> a replacement for the Tube ULA in most wedge co-pros, notably where the
> co-pro would work on a Beeb but not on a Master 128, because it's timing
> is a little different.  However it wasn't recommended for use in ACWs,
> though I'm not sure why.  IIRC it had problems with 32016 co-pros (eg
> Master Scientific).
>
> So if you're going to make a copy, I'd say copy the original ULA.

There is a third chip, made by AMS

http://www.retroclinic.com/misc/tubechips.jpg

It maybe a cousin of the AMI one, as both come from Austria it seems. I've 
also not seen the one on the daughterboard, do you have a pic?

Mark.