Fw: TU58 yet one more time

[Tony Duell]

Yes, it's still me. My normal ISP seems to have installed spam
filters (without warning me!) which (a) drop the classiccmp messages
and (b) bounce most outgoing mail!


> On Monday, 30 May 2016, 23:37, shadoooo <shadoooo at gmail.com> wrote:
> Hello,


[...]

> the device will be able to control the tape speed and to sample with ADC> and DAC the analog signals on the read / write heads, transferring the bare
> samples with almost no filtering to a PC.


When I was fiddling with the tape drives in my 11/730, I pulled the 

8155 from the controller board so I could control the tape motion 

by pulling signals low with wire links, I then hung a 'scope off the
output of the read amplifier. I found that most (old, defective) tapes
gave a very weak singnal, and that the flux transitions wrre almost 

equally spaced. I think you would not be able to recover anything from
that. But you can but try.


As an aside, I assume you've looked at the DEC data recovery circut. It's
clever. It's almost indpendant of tape speed. Basically, ramp up on the 

transition at the start of a bit cell, change to ramp down on the second
transition, then sample and reset, and start to ramp up again on the 

transition at the start of the next bit cell. Depending on whether the 

sample at the end of a bit cell is +ve or -ve it sees if it's a 0 or 1 


[...]
> But I have to fix the capstan too...


Now that I have done. I started off with aluminium alloy rpd (I think
1/2" diameter, but I can check my notes), turned it down, turned a 

groove for an o-ring, drilled the centre hole (oddly for a US machine
this is 3mm, not 1/8" -- and note the motor has different diameter 

spindles on the 2 ends!) drilled and tapped for the grub screw. With
a good tape I get a good, stead signal at the right speed at the output
of the read amplifier.


-tony