Wang Series 700B Advanced Programming Calculator Refurb.

[durgadas311]

It could be that the head characteristics are different than the original.

 

[BlaBla1985]

It could be that the head characteristics are different than the original.

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.

 

[Chuck(G)]

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).

 

[durgadas311]

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.

 

[BlaBla1985]

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.

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.



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.

 

[durgadas311]

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.

 

[BlaBla1985]

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.

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...

 

[BlaBla1985]

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.

 

[JimLou]

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.

​

 

[durgadas311]

@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):

 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?

 

[atariquest]

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

 

[Djchili]

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.

 

[BlaBla1985]

@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):

 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?

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.

 

[BlaBla1985]

@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):

 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?

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.

 

[durgadas311]

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.

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.

 

[BlaBla1985]

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.

If you need anything else tested, let me know.