test-drb February 2020

test-drb@ccmp.vtda.org

95 participants
82 discussions

by cctalk＠ibm51xx.net

Hello All,Recently I tried making some custom SCSI cable. In the past I have successfully made my own 50pin SCSI and Floppy cables with out much issue. However, I am finding it almost impossible to crimp the HD68 connectors on the cable. I have even tried a vise grip and I still couldn't get it to crimp all the way down. Anybody with some advice? Is there a trick I am missing? TiA.

4 years, 10 months

VAXmate PSU Failure

by robert.jarratt＠ntlworld.com

A little while back I posted here because I needed help with analysing the failure of the PSU from my VAXmate. Since then I have had some comments on the reverse engineered schematic which I have now improved and which is here: https://rjarratt.files.wordpress.com/2020/02/h7270-control-pulse-width-modul ator.png Following advice from a list member, I have been looking at the 555 and the PWM that control the switching transistor, using a bench power supply to power the PWM directly (across pins 5 and 7). When I do this, I find that Vref from the PWM, which should be 5V to power the 555, does not reach 5V. I have tried removing the 555 from the circuit, and when I do this Vref goes to the nominal 5V, once Vcc to the PWM is above 16V. However, if I put the 555 back in, then Vref only goes to 2V. I have socketed the 555 and tried with two other brand new 555 chips, the result is the same. It seems that just adding a 555 kills the Vref output of the PWM. It can't be anything else in the circuit because everything else is still in circuit when the 555 has been removed. Could the PWM be faulty? Perhaps it can't provide enough current to bring Vref up to 5V once the 555 is in the circuit? Any suggestions gratefully received. Regards Rob

4 years, 10 months

Teac FD-54

by vax＠purdue.edu

I've got a couple of Teac FD-54B's that appear to have problems with their index sensors. Does anyone have any docs for these? The internet seems to barely know they exist vs the FD-55, which has info everywhere. I'm thrown off a bit by the 3 wire phototransistor (vs the common 2 wire ones) they they use, and I haven't quite disassembled it enough to figure out a part # for that. Also, if anyone has a pair of spare black FD-55B, that'd be useful too. Patrick Finnegan

4 years, 10 months

large HP DesignJet plotter needs a good home

by shumaker＠att.net

Classic heavy duty HP Designjet 755CM C3198B? in search of a new home as it's now one stop short of the e-waste people. It's large? (handles a 36in roll) and has the usual DesignJet stand.??? I can even include some NOS ink cartridges. It would need a horizontal belt as they deteriorate even without use but otherwise in good shape; it was fully functional when I removed it from service. I'm not trying to sell it, I just hate to trash it. Not easily shippable, it's located in the Santa Cruz area - I could deliver it here in the bay area if someone wants it. Steve

4 years, 10 months

Happy 74th Birthday ENIAC

by blstuart＠bellsouth.net

On this, the 74th anniversary of the unveiling of the ENIAC, I've decided to post a couple of things I've been working on. The first is the 3D model of the ENIAC mentioned before. It's designed using brlcad, from the Ballistics Research Lab. It just seemed too appropriate to model it using the tool devleoped where it lived. The thingiverse link is: https://www.thingiverse.com/thing:4164825 The second thing is a draft of a chapter from a book I'm in the very early stages of. It describes the basic circuit designs used in the ENIAC with SPICE simulations of them. The layout and formatting are based on the old Army Technical Manuals of the time. http://cs.drexel.edu/~bls96/eniac/ch1.pdf Enjoy, BLS P.S. Apologies if you got this multiple times; I've posted it to a few lists I'm on.

4 years, 10 months

Sun external SMD cables

by aperry＠snowmoose.com

Anyone here have a set of Sun external SMD cables (530-1079 and 530-1080) that they can loan or want to sell? I ordered from a set from MemoryX at the beginning of Jan. They haven?t arrived and MemoryX isn?t answering my e-mail asking what?s up. alan

4 years, 10 months

Respond to items I offer offlist please

by couryhouse＠aol.com

Respond to items I offer offlist please

4 years, 10 months

Have extra ge. G11a. First GE landmark transistor for counter and computer cicurits

by couryhouse＠aol.com

Ok offer me offlist for our extra transistor unused? in box sealed in original cellophan6... Have extra ge. G11a. First GE landmark transistor for counter and computer cicurits Germanium Whisker Transistors ? Robert Hall returned to General Electric Research Laboratories Schenectady just as Bell announced its point-contact transistor.??Hall had just graduated PhD from Caltech and had previously worked at the laboratories on a range of projects including the Harper North Wartime radar diode project. Dr Albert Hull was Assistant Director of the Laboratory. He was known for his collegial management style with a relaxed approach to the research agenda of his staff members. Hall recalls that Hull came in with the reprint of the Physical Review letters that announced the transistor [Bardeen 1948] and said ?Robert here?s an interesting development from Bell Laboratories. It looks like something pretty new and exciting. Would you like to look into it and see if there?s anything interesting there.? [Choi 2004] General Electric had all the knowhow it needed to duplicate the Bell design quickly. North?s diode programme had diodes that could handle 100 volts back voltage which was state of the art at that time. (Purdue University produced the high back voltage germanium for the Bell point contact transistor.) North?s diode programme and related research ensured it had a manufacturing understanding of the key technologies: High back voltage poly-crystalline germanium; Doping; Point contact design; Welding or forming; and Assembly and encapsulation. Its first designs were crude with two pins for the collector and emitter with the base connection through the case in the manner of the Bell Type A. No socket was available and users were recommended to use a 5 pin subminiature tube socket using positions 2 and 3 for the collector and emitter and to create a base connection by inserting phosphor-bronze strips in positions 1 and 4 and bending them so they contacted the transistor case. The transistors were known as germanium triodes or germanium whisker transistors. Two types were produced evolving from prototype coding through the familiar ?G? designation in use for its point-contact diodes and finally adopting RMA registration: ? ? Prototype G Series RMA Amplifier/oscillator SX-4A G11 2N30 Switching Z2 G11A 2N31 Date Up to 1951 1950 on 1952 on ? The prototype numbers appear in early data sheets and in a General Electric price list dated June 1st?1951 in which the new SX-4A and Z2 transistors were priced at a massive $29 each. The two transistors had the same mechanical and electrical characteristics but the switching transistor was tested for ?trigger action? or negative resistance. [General Electric 1950 courtesy Jack Ward] >From 1952 the transistors had 3 pins with the base connection being soldered to the outside of the transistor?s case. See data sheet ECG-3B. Early General Electric G11 and G11A point-contact transistors.[Courtesy Jack Ward] Production General Electric G11 point-contact transistor [Courtesy?Jan de Groot]

4 years, 10 months

d-112 users handbook. Have xtra copy...

by couryhouse＠aol.com

Have xtra copy of. Digital computsr controls inc.? d-112 users handbook offers?????

4 years, 10 months

"itt courier nibble computer" have discovered 2 unpopulated boards ca.1981 there was a,plant in phx.....for IBM cluster terminals....

by couryhouse＠aol.com

"itt courier nibble computer" have discovered 2 unpopulated boards ca.1981? there was a,plant in phx.....for IBM cluster terminals....

4 years, 10 months

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test-drb February 2020