-----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Patrick O'Keefe Sent: Monday, June 30, 2008 3:13 PM To: IBM-MAIN@BAMA.UA.EDU Subject: Re: David Caminer (1915-2008)
On Mon, 30 Jun 2008 15:30:58 -0400, Thompson, Steve <[EMAIL PROTECTED]> wrote: ... >No, the writer is quite technically astute and meant that the vacuum >tube circuits with their chokes, coils, etc. were ELECTRICALLY noisy. >... You may be right. You are definitely giving the author more credit than I did. I did briefly wonder if he might be talking about microphonics, but decided that would have been a possible issue in an analog system but would have been causght as a dead device by whatever error detection was (hopefully) used. I don't remember what vacuum tube logic circuits looked like. Are you sure they were much noisier than the transisterized circuits that replaced them? <snip> Well, given the Faday shielding that was needed between stages of certain tube-type radios to prevent inductive coupling... And then there are the formulae for gauss. If you take the B+ (200-500VDC) for the plate voltages (I seem to recall that logic only used Triodes, and possibly dual Triodes), add to that the speed at which you would want to change to grid voltage (from "open" to cut-off to give 1/0 or 0/1), and you will generate a very noisy square-wave. And unshielded leads acted like acted like antennae. And then, you could sometimes cross-couple circuits because of a bad choke/capacitor to shield one stage from another using the same B+ feed... Man does this take me back a few years. I haven't used those formulae in years and just realized I've all but forgotten all of them. Now, going to transistors, one had to be very careful to avoid cross coupling between layers (inductive and capacitive), or you would generate noise into another circuit... But the big difference is, lots of voltage = large electromagnetic field. Low voltage with low amperage = small electromagnetic field. Tubes use large voltage differences, solid state uses small differences. Regards, Steve Thompson -- All opinions expressed by me are my own and may not necessarily reflect those of my employer. -- ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
