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Wang Series 700B Advanced Programming Calculator Refurb.

durgadas311 said:
It could be that the head characteristics are different than the original.
Click to expand...
Probably, but it reads back normal tapes fine. I was looking over the full signal it recorded and let's say it's not perfect. I could see multiple points where the recording into Audacity was so close to nothing that I can't fault the machine for not reading it properly.

I think for it to work I'll need to align the head in the cassette adapter to the head of the tape drive to get maximum signal. The annoying part is I can only get to the set screw and head terminals with the top of the machine. I'll have some time Sunday to play around with it.
 
Most audio heads are designed to be used with an AC bias during recording. I suspect that the Wang 700 uses simple saturation-mode recording. I don't know if this makes a difference in the write performance, however--it could be that you're recording on the wrong part of the hysteresis curve.
I might have a digital tape head in my stash, but it's probably 2-channel (clock+data).
 
It's possible that the record mode is not optimal for the head. If we knew things like how much flux per milliamp (or however they measure that), we might be able to tune the series resistor (6.4K in your case) to send more current through the head during record. But, you don't want to burn out the head, either.
 
durgadas311 said:
It's possible that the record mode is not optimal for the head. If we knew things like how much flux per milliamp (or however they measure that), we might be able to tune the series resistor (6.4K in your case) to send more current through the head during record. But, you don't want to burn out the head, either.
Click to expand...
Well... you mentioning this gets me thinking... what about the resistors in the cassette adapter? What if those were changed to allow a stronger signal to exit the adapter? There is a little PCB in the cassette adapter with 4 resistors on it, 2 per channel... looks like 3200 Ohms if I'm reading them right.

cassette4.jpg

This would prevent any damage to the 700B by messing with internal components. And modding it could be as simple as bridging out 1 of the 2 resistors to quickly change the total value.
 
Oh, I thought you were using real tape. If you are feeding a signal through the adapter, then it is certainly possible that the signal is too weak.
 
durgadas311 said:
Oh, I thought you were using real tape. If you are feeding a signal through the adapter, then it is certainly possible that the signal is too weak.
Click to expand...
No, I was doing a quick test loading the test data of 200 "0" that I wrote to tape last weekend into the machine, then switching the real tape out for the cassette adapter and try to record the signal into Audacity on a laptop through the microphone jack.
And then switching the jack to the headphone jack and play the recorded signal back in to tapedrive to see if it would load the test data back into memory.

It can read and write to real tape with no issue now. One of the blank sides of a tape I had now has the test data set on it and a couple of short test programs from your emulator and the manual. That all seems to work quite well.

But it seems that the alignment of the tape head in the drive and the head inside the cassette adapter isn't great (as the output signal varies a lot). It may also get quite distorted due to the ammount of amplification I have to give it while playing it back into the 700B, or maybe it's the fact I'm using the microphone jack instead of a AUX input (I should have audio in jacks on the sound card in my main PC i think).

Lots of thing to try out this weekend...
 
It's working with the cassette adapter now, it's just really difficult to align the 2 head perfectly so the signal stays strong enough. I just managed to get a pretty strong and clean signal into Audacity and with that signal on 100% volume for playback (but no extra dB added) it loads the 200 "0"'s test data perfectly and stops automaticly at the end.
Audacity001.png
 
Is there an update to this thread? I would love to hear what BlaBla1985 is doing with this machine. I taught myself to program a 700B in the early '70s which lead to a career programming Wang 600s, 700s, 2100s, VPs and MVPs. I just discovered the simulator that durgadas311 wrote and have been having a great time remembering and relearning this fascinating old creaker.

​

 
@BlaBla1985 Is your 700 still working? I have a question about operation of the STEP button when stepping through a program in RUN mode. It seems that when a SEARCH command is reached (or subroutine call), that the 700 starts running again and you lose the ability to continue stepping. I was using this program on my simulator (which is running Wang 700 microcode):

Code: 
 0000   04 08  MARK
 000l   07 00  E0
 0002   07 0l  E1
 0003   07 02  E2
 0004   07 03  E3
 0005   06 00  +
 0006   04 07  SEARCH
 0007   07 00  E0
 0008   05 12  END

And as I STEP through it, it takes off running after the stepping through SEARCH E0. Can you confirm whether a real 700 acts this way?
 
Those smaller capacitors were made by Sprague. They were acquired by Vishay in the 90s. Luckily, they still manufacture the TE series of capacitors. They are expensive for a capacitor $2-8, but that is not too bad. https://www.vishay.com/docs/42042/te.pdf
I think these are special order, which mean you have to have a large minimum order and long lead time. However, you will be able to find them on secondary markets.

Marvin
 
Wow, awesome stuff. My dad worked for Wang for years. I have more Wang parts and electronics in this basement than I know what to do with. Let me know if there is something you need.
 
durgadas311 said:
@BlaBla1985 Is your 700 still working? I have a question about operation of the STEP button when stepping through a program in RUN mode. It seems that when a SEARCH command is reached (or subroutine call), that the 700 starts running again and you lose the ability to continue stepping. I was using this program on my simulator (which is running Wang 700 microcode):

Code: 
 0000   04 08  MARK
 000l   07 00  E0
 0002   07 0l  E1
 0003   07 02  E2
 0004   07 03  E3
 0005   06 00  +
 0006   04 07  SEARCH
 0007   07 00  E0
 0008   05 12  END

And as I STEP through it, it takes off running after the stepping through SEARCH E0. Can you confirm whether a real 700 acts this way?
Click to expand...
It should still work, I moved it off the bench to work on the MAI minicomputer. Since that beast is back together now I'll grab the Wang again and see if I can test that code. Just need to clean up the workbench a bit.
 
durgadas311 said:
@BlaBla1985 Is your 700 still working? I have a question about operation of the STEP button when stepping through a program in RUN mode. It seems that when a SEARCH command is reached (or subroutine call), that the 700 starts running again and you lose the ability to continue stepping. I was using this program on my simulator (which is running Wang 700 microcode):

Code: 
 0000   04 08  MARK
 000l   07 00  E0
 0002   07 0l  E1
 0003   07 02  E2
 0004   07 03  E3
 0005   06 00  +
 0006   04 07  SEARCH
 0007   07 00  E0
 0008   05 12  END

And as I STEP through it, it takes off running after the stepping through SEARCH E0. Can you confirm whether a real 700 acts this way?
Click to expand...
Interesting...
Mine doesn't, I can keep stepping through it over and over and it will add 123 to the top register and then loops back. It doesn't go into RUN mode. Granted mine is a 700B, I'm not sure if there are many differences between the various versions in the microcode for things like this.
 
BlaBla1985 said:
Interesting...
Mine doesn't, I can keep stepping through it over and over and it will add 123 to the top register and then loops back. It doesn't go into RUN mode. Granted mine is a 700B, I'm not sure if there are many differences between the various versions in the microcode for things like this.
Click to expand...
Thanks! This confirms (yet another) microcode transcription error. I'll have to go through and try and debug that. It's been a long time since I used the microcode debugger on the Wang 700 simulator, so there's a re-learning curve.
 
Since I have some free time I wanted to do something I've been wanting to do for a while, try and read back some of the programs on the cassettes that came with the machine. And see about backing them up to an audio file on the PC using the adapter. There is also a copie of a hand written manual for these programs among the documentation I got with the machine, it would be nice to have all that stuff backed up safely.

The first set back on this... some of the tapes have faired very poorly over the past decades, especially the lower numbers seem to have damage to the actual media. I think most of the programs have multible copies spread across the tapes. Although the numbers on the tapes suggest there might have been more tapes. Now some B sides are labeled as results from calculations on the A side, so it might just be that the result tapes have not all survived.

The second... I'm not sure the tape drive is 100%. When it runs for a bit it starts to squel a bit (as if the clutch is slipping) and sometimes it stops pulling the tape along. This might also be due to the age of cassettes I guess. It's certainly not helping with getting something off the tapes.

And third, IF some data comes of a tape, the machine gives an instant Machine Error. So there is a possibility that the replacement head is unable to pick up the signal written with the old head correctly. This might also be an alignment issue between the new and old head.
 
Interesting... I ordered one of those cheap cassette players that have a USB connection so one can "Back up" their collection of music to MP3. This price bracked might not deliver much quality when it comes to audio, but all I want to do is get the data signal off the tape.

Now, I have been using the 1 blank tape I got with the machine as a test tape for the new tape head, writing various test programs to tape and also to my bench laptop using that tape adaptor.

I now used that USB tape player to read back both my test tape and the old tapes made 40+ years ago and there is a very clear difference in the signal...
So, this is my test tape, made using the new tape head:
NewTape.jpg

And this is from one of the old tapes written with the original setup:
OldTape.jpg

And while the short pulses look close enough, the long pulses look reversed. There may also be a bit of volume lever difference between the 2 signals (which the machine can be picky about when using the cassette adaptor to load).
I have tested 3 different old tapes and all 3 show the same long pulse.
 
The traces might be more alike than it first appears. The new recording shows all the "long" pulses starting from the -1 position, while the old tape shows the long pulses starting from the +1 position. This is somewhat random, as it depends on where the last data bit left off. The thing both have in common is that on the long pulses the transition takes longer - presumably because it has more time.

The Wang 700 is looking for flux change "blips" coming from the tape head. I'm not sure how that relates to the signals you're looking here from the USB tape reader. So, it difficult to imagine what the 700 sees for each tape.

But, one thought, perhaps the difference in polarity is indicating that the new tape head is actually hooked up "backwards", and so the flux transitions are appearing reversed and it is confusing the 700. New tapes were made using the backward head hookup, the same as the reading, so that might explain why new tapes work and old ones do not.
 
durgadas311 said:
The traces might be more alike than it first appears. The new recording shows all the "long" pulses starting from the -1 position, while the old tape shows the long pulses starting from the +1 position. This is somewhat random, as it depends on where the last data bit left off. The thing both have in common is that on the long pulses the transition takes longer - presumably because it has more time.
Click to expand...
Ah, I had not thought about that. But it does make sense. There is only one way to install the tape head, but I could check the wiring. I was thinking about a change in either the inductive of capacitive properties of the head... but an inverted signal makes a lot more sense.

This might also mean that simply inverting the recording of the old tapes could fix it. Although I would still have to find the right volume to play them back at. But that can be found using the new tape as a baseline.
 
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