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Thread: A new G888 manchester read/write module

  1. #11
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    Quote Originally Posted by Al Kossow View Post
    In particular the TC-12/TC-08/TC-11 where the preamps are in the controllers, not at the drive,
    and the preamp and limiter are high gain.
    And they are very good at amplifying noise.

    Quote Originally Posted by Al Kossow View Post
    I really need to get back to DECtape/LINCtape archiving.
    I may just use the same setup this time as I'm using with 7-track tape and just stay in the analog digitization domain.
    Can you tell us a little more about how you would archive a LINCtape?
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  2. #12
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    Quote Originally Posted by Al Kossow View Post
    You might try moving the G888s to their slots inside the TU56 and re-cable
    I just looked at the PDP-12 maintenance prints. The TC12 LINCtape controller uses G882 modules instead of the newer G888 modules.
    Putting G888 modules in the TU56, and then splicing the TTL outputs from the G888 into the TC12 controller would be a big challenge.
    We made an LT-Spice simulation of the G882 module.
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  3. #13

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    Quote Originally Posted by Al Kossow View Post
    I may just use the same setup this time as I'm using with 7-track tape and just stay in the analog digitization domain.
    Curious question, how do you do archiving of tapes? What is the best way to go? Do you sample the analog signals and do all post processing on a PC?

  4. #14
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    Quote Originally Posted by anders_bzn View Post
    Curious question, how do you do archiving of tapes? What is the best way to go? Do you sample the analog signals and do all post processing on a PC?
    The last time I did this for DEC/LINC tapes I used a TU56 with internal G888s and a FIFO attached to a PCI parallel port card on a Macintosh G3
    The decoding in the digital domain was pretty straightforward and has been up at http://bitsavers.org/projects/dectape/ for a while, such as it is.
    It is all pretty intertwined with the PCI card setup but the basic track decoding should be obvious.

    What I would do today is use a Salae and digitize the preamp output doing all of the processing on a Linux box. Dealing with the variable
    speed clock and the self-oscillation of the preamps as it comes up to speed would be trickier in the analog world. Clocking the FIFO from
    the clock track made it mostly transparent doing it digitally. Bringing a few test points out to the front edge of a redone G888 would make
    attaching probes to do this easier.

    Several decades ago now, someone I know split the redundant heads and read both separately, but that probably poses too much risk now
    damaging irreplaceable head stacks.

  5. #15
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    Quote Originally Posted by Al Kossow View Post
    Clocking the FIFO from the clock track made it mostly transparent doing it digitally.
    I think that the LINCtapes and DECtapes use the opposite phase output from the G882/G888 for the clock track.
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  6. #16

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    Quote Originally Posted by Al Kossow View Post
    The last time I did this for DEC/LINC tapes I used a TU56 with internal G888s and a FIFO attached to a PCI parallel port card on a Macintosh G3
    The decoding in the digital domain was pretty straightforward and has been up at http://bitsavers.org/projects/dectape/ for a while, such as it is.
    It is all pretty intertwined with the PCI card setup but the basic track decoding should be obvious.
    I think you have written about this earlier.

    Quote Originally Posted by Al Kossow View Post
    What I would do today is use a Salae and digitize the preamp output doing all of the processing on a Linux box. Dealing with the variable
    speed clock and the self-oscillation of the preamps as it comes up to speed would be trickier in the analog world. Clocking the FIFO from
    the clock track made it mostly transparent doing it digitally. Bringing a few test points out to the front edge of a redone G888 would make
    attaching probes to do this easier.
    Or just do a simple preamp PCB that sticks into the free slot besides the data cable to the controller. Anyway, I can easily add pinheaders to the board and try this out. I can borrow a Saleae and record analog data if someone is curious to try to make something out of it.

    Quote Originally Posted by Al Kossow View Post
    Several decades ago now, someone I know split the redundant heads and read both separately, but that probably poses too much risk now
    damaging irreplaceable head stacks.
    Make sense, but I do agree that this operation is to risky.

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