test-drb February 1999

test-drb@ccmp.vtda.org

178 participants
709 discussions

by dogas＠leading.net

Hi, If anyone is in the Chicago area and wouldn't mind a (several heavy items: multiple TRS-80 16b and 6000HD systems) pickup and subsequent packing/shipping job expenses paid with maybe a system or two ( ;) ) thrown in for effort Please send email Thanks - Mike: dogas(a)leading.net

25 years, 11 months

tube CD player (was Re: sizes (was Re: vacuum tube computer))

by Philip.Belben＠pgen.com

Eric has replied to my post with a lot of good points, but I don't understand this one: > After you do the D/A, you have a huge amount of sampling noise at Fs/2 (and > its harmonics). For a CD player, Fs is 44.1 KHz, so the sampling noise is at > 22.05 KHz. Since the desired audio frequency response extends to 20 KHz, a > non-oversampled player needs "brick wall" analog filters, with a pass band to > 20 KHz, and a stop band starting below 22.05 KHz. > > Digital oversampling is used to move the sampling noise to a higher > frequency. 4x oversampling moves it to 88.2 KHz. The oversampling filter > is a low-pass filter, so the audio content still has a frequency response > to somewhere above 20 KHz. But now your analog filter can have a much > shallower slope, which is easier to implement and introduces much less > phase distortion. > > Your analog oversampling scheme does not eliminate the noise at Fs/2, > and in fact introduces more sampling noise at higher frequencies. It does > not help reduce the requirements of the analog filter. Don't confuse sampling noise with quantisation noise. Quantisation noise is due to the replacement of an analogue value by a digital representation not exactly the same; it is reduced simply by having more bits of precision (there are other tricks, including things involving oversampling, but they only cloud the issue). Sampling noise is present in a sampled waveform whether it is a sequence of digital numbers or of analogue values. It arises from the deviation between the original waveform and the sampler output (with no filtration at all this is a series of steps) at the intermediate points between samples. Oversampling interpolates intermediate samples, and uses a filter to reduce the sampling noise due to not having known what those intermediate values should have been. While I admit that the linear interpolation I described is a rotten oversampling filter - it was only mentioned by way of an example - the mathematics are the same whether you use a digital computer to generate the digital numbers at your oversampled points or a switched analogue circuit such as I described to generate analogue values at the intermediate points. This analogue circuit can also (theoretically) reduce quantisation noise even compared with digital oversampling, since the intermediate values are not limited to the precision of the DAC. In practice, quantisation noise probably is probably slightly higher, since the intermediate values are limited to the precision of the resistor networks that derive them. So why does this sort of analogue filter not reduce the sampling noise at Fs/2? If it introduces noise at higher frequencies (which I agree it does), this is because the noise arises from conversion of samples to a continuous function, not from conversion of digital to analogue. > The logical extreme of oversampling is to use such a high factor that you only > need one bit of data. This is called a delta-sigma D/A converter. For 16-bit > source data this would require at least 65536x oversampling, but there are > some tricks to reduce this to e.g. 128x. This is the basis of the so-called > "1-bit" D/A converters. The advantage is that you only need a single-pole > analog filter (and in practice can get by without even that), and that the > tradeoff from quantization to time domain has been maximized, which is good > because it is much easier to get high precision in the time domain as > described above. I have met delta-sigma encoding, but I never managed to work out how you get the sampling rate down to a manageable value. Since we're getting a bit off topic here, could you post not an explanation but a reference to somewhere I can look up this particular aspect of the problem. Philip.

25 years, 11 months

3-phase (was: Re: CDC 9766 Drive and packs)

by amirault＠epix.net

Hi, OK. What you are saying is that you have a functionally obsolescent electric service that needs to be upgraded to a 200 amp service to better handle todays electric needs. I suggest that you contact your electric company and find out how much this upgrade will cost you. John Amirault -----Original Message----- From: Eric Smith <eric(a)brouhaha.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, February 04, 1999 3:34 AM Subject: Re: 3-phase (was: Re: CDC 9766 Drive and packs) >> Why not just go out and BUY a three phase converter? You know that such a >> thing does exist now. > >As the person that started this thread, I can certainly explain why *I* >don't buy one. > >The equipment I want to run will need about 45A per phase. If I had >an 85% efficient converter, I'd need an 80A 240V circuit. The entire service >entrance to my house is only 100A, and I use more than 20A of that for >lighting alone, not to mention the microwave oven, audio and video gear, >and modern computers. > >Normal US homes are not wired for big old computers and their peripherals. > >

25 years, 11 months

web archive & listproc help (was: Collecting computers - the book...

by cfandt＠netsync.net

Upon the date 09:42 AM 2/3/99 -0800, Kevan Heydon said something like: > >As the creator of the web archive I feel I should reply... > >On Wed, 3 Feb 1999, Hans Franke wrote: >> >> Me_Too(TM) don't feel comfortable with a _public_ archive of this > >If other people are of the same opinion then I will take down the web >archives. Kevin, isn't there a way to completely hide this archive from any search engine? I'm no web weenie so others here who are should jump in and answer. Links that ClassicCmp folks put on their pages to the archive do, of course, blow the cover. What if we just have an unannounced or "secret" URL for the archive? List members could be given it and a note placed prominently on each archive page stating this is priviledged information and not to be publicly released because of unprotected email addresses or something. List members will just have to write the "secret" URL on a Post-it note and place it on their computer or tack board. Passing of it to new members or those of us who have lost the addr. would be given it only by private email. Well, it's just an idea. This list is, in my opinion, a very significant source of technical and anecdotal infomation about our old machines the likes of which probably could never be found elsewhere. I've learned so _very, very_ much from many of you since 10 December, 1997 when I joined. Witness the recent IBM 1130 thread. We found more info relating to them and a working system in Germany! I've got DEC gear in my collection which several have been helping me on it. I really hope I helped a few of you too. It's been discussed here before, and again I'll state that it's a pet peeve, that some really important tidbits of info on our classics is not found by any search engine that I know of. So there seems to be some way the pages are hidden. In this case of securing our ClassicCmp archive's privacy, the pet peeve is hereby released :-) I can always use the 170MB (and now growing at a rate of about >12MB a month) of disk space they take at the moment. Instead of cluttering >the list send mail to me directly at kevan(a)heydon.org and I will count the >votes. I'll send you a vote privately but I do want to say the archive is a very important resource (flame wars and very off topic junk excepted of course). I think nearly all of us feel access to it is needed no matter where it is kept. The U. of Washington archive site is not available since haliotis is shut down. >> list. I considere this more privat - and for the pe(a)rls in here, >> I made up two archives (_on_my_hard_disk_) - one where every pice >> is stored, and one where I put the very genuine things. So I have >> any possible search option (fast and local) and privacy (i hope). > >I also tend to keep post that I think will be usefull (which happens to be >most of Tony Duells posts) in a mail folder. I have also been keeping >entire threads with a thought to extracting the pearls of wisdom into web >pages. > >It is much less work to archive the entire list than it is to manually >extract particular bits of information. It is also easy to let the major >search engines trawl the list archive to allow searching. > Regards, Chris -- -- Christian Fandt, Electronic/Electrical Historian Jamestown, NY USA cfandt(a)netsync.net Member of Antique Wireless Association URL: http://www.ggw.org/freenet/a/awa/

25 years, 11 months

New stuff: Televideo docs, Dapple computer and rack mount Apple II

by rigdonj＠intellistar.net

New stuff: I went scrounging yesterday. I bought stack of new Televideo manuals. I got: (book 1) Televideo TS 802H Computer System Installation and User's Guide with the quick reference guide, packing list, Digital Reserce lincense for CPM, errata sheets, customer quality survey, F1-40 print sample, a brochure >from TRW about maintenance service and several addendum booklets. Looks pretty cool. Has anyone got one of these that they don't need? (book 2) Operator's Manual Model 950 (new in sealed package). (book 3) Televideo TS 800A, TS 802 and TS 802H Maintenance Manual. This is THE best maintenance manual I've ever seen! It not only includes the maintenance information and schematics but also spares kits inventory listings, complete parts lists and prices, parts specifications, board drawings, circuit descriptions and theory of operations, timing diagrams, etc. (book4) Televideo Model 925 CRT Terminal Installation and User's Guide. (book 5) Model 925 Maintenance Manual. If anything, this one is even more complete than the one for the 802! It even includes the original Rockwell Data sheets for the 6522 VIA, 6545-1 CRT controller, and a prelimiminary data sheet for the Intel 8048H/8048-1/8035HL/8035HL-1 8 bit microcomputer ICs. It also includes another copy of the CRT Terminal Installation and User's Guide, a Terminal Troubleshooting Guide and additional service bulletins and sales literature for the Televideo terminals. I also got several boxs of CPM disk but I haven't sorted them all out yet. I haven't found the Dapple computer that I spotted several weeks ago but I found another one!!! (At least this one is clean!) I'll give details when I've had a chance to look it over. I also bought an Apple IIc in a 19" rack mount! It operates a gas analyzer sytem and was put together in the UK. I haven't picked it up yet so details will have to wait. Joe Joe

25 years, 11 months

Meta-4 manuals

by drbilling＠ucdavis.edu

Sorry, I don't have any way of putting the two manuals on-line and they are in storage as I am in the process of moving. > ... >Any chance of putting these on-line or of us getting a copy? The Meta-4 >sounds like an interesting machine. > >Who on this list can honestly say that they have never thrown out >anything that they now regret? --Dean

25 years, 11 months

3-phase (was: Re: CDC 9766 Drive and packs)

by Philip.Belben＠pgen.com

>>My parents have 3-phase electricity at home, but I don't (yet). But I >>think it's more common in the UK than in the US. (BTW my parents have a >>16th century farmhouse which they heat electrically during the winter. >>Maximum load we've measured, 36kW.) > > 36kW!! Ouch! And cost of electricity is, I understand, higher than in the > US, true? Except Jamestown, we pay only $0.03565 per KWH :-) so electric > heat is not such a financial killer for homeowners (or for nuts like me > with working big iron computers in the basement). Dual tarriff (?sp) is quite common. The most usual scheme is called "economy 7" which charges about 14c US per kWh during the day and somewhat less (I think it's less than 5c - sorry, I am not in the UK this week so I can't check) for a seven-hour period starting at midnight +/- one hour (exactly midnight on older installations). Some circuits - mainly heating - are controlled by the same timeswitch (older installations) or radio receiver (newer ones) as the tarriff selector on the meter. It is said that many night clubs use economy 7 tarriff despite no heating load... Other schemes exist. One called "heatwise" also gives you a couple of short periods of cheap power during the day... > Yes, very few private residences in North America have 3 ph power _unless_ > it was asked for and installed, of course at an extra co$t. If someone has > a garage or machine shop at home (and the local zoning laws permit it) then > 3 ph can be installed. Otherwise, bigger apartment buildings, larger > offices and factory buildings are usually wired for 3 ph at 240 volts or > 480 volts. Gosh. I've seen 3-phase 208 volts in the US, but what would they use 240 for? Philip.

25 years, 11 months

apple2 fun

by SUPRDAVE＠aol.com

In a message dated 99-02-03 20:23:32 EST, you write: << Well, if you're in BASIC you can type the command BYE to go into a program launcher. Hoepfully you have something good like Bird's Better Bye installed so you don't have to type in the entire pathname when you're ready to restart. Sellam >> The BYE command sucks! i've never seen a more user unfriendly program in my life. it doesnt give a chance to browse any directories or disks. if you dont know the pathname you want to goto, it is useless. i always end up doing pr#6 anyway. any programmer that uses it obviously doesnt use the program. it's always more helpful just to be dropped to a basic prompt.

25 years, 11 months

RT-11: ?DIR-F-Invalid directory

by mbg＠world.std.com

>I don't think there is any more need too bother with this train of >thought. Thanks to the tips that Jerome gave this morning on how to >create that dump, I was able to inspect the first 20 or so blocks, and I >think I can safely say that the disk is a lost cause. Blocks 0-?? are >totally toasted. I don't know how I managed it, but apparently I did >something that caused the SYSGEN to write to there last night, it's got a >binary image where there should be a directory structure. Sounds like >the next time I try something like that I'd best turn the LA75 on as a >console printer first so I can analyze what I did wrong :^/ It does sound like what I thought it was... But remember, the disk may not be a total loss... many, if not most, of the files are most likely still there (I'm expecting that sysgen simply overwrote the beginning of the disk with each of the .OBJs... so the amount of corruption would be no more than the largest .OBJ produced. So, later directory segments would be okay, and there would be sufficient info in them to recover those files. Earlier files would still exist, following the directory... remember, they are contiguous files, so if you find the start of one, you can get the whole file back. There used to be a utility someone wrote, ndump, which looked at the first n bytes of each block and reported on them... that way you could figure out at least where your ascii text/source files were... and RT provides commands which would allow you to grab just the blocks of the disk needed to get a file... It is possible, just procedural and time consuming... but if there is information which is important enough, it is worth it... >Thanks to your pointing out that the backup command is backup (Um, that >was just a little to obvious) I'm now backing DU3: up, since I've got >part of what was on DU2: on it. However, that still leaves me with a >logical disk MACRO.DSK that I would like to recreate. With the directory >toast, I guess that isn't easy. So..... If you can find the beginning and end of the file... you can probably restore it from the corrupted disk in its entirety... Megan Gentry Former RT-11 Developer +--------------------------------+-------------------------------------+ | Megan Gentry, EMT/B, PP-ASEL | Internet (work): gentry!zk3.dec.com | | Unix Support Engineering Group | (home): mbg!world.std.com | | Compaq Computer Corporation | addresses need '@' in place of '!' | | 110 Spitbrook Rd. ZK03-2/T43 | URL: http://world.std.com/~mbg/ | | Nashua, NH 03062 | "pdp-11 programmer - some assembler | | (603) 884 1055 | required." - mbg | +--------------------------------+-------------------------------------+

25 years, 11 months

Need help on old Tandy stuff -- Allison? Anyone else?

by dogas＠leading.net

-----Original Message----- From: Doug <doug(a)blinkenlights.com> >But the workSlate was in another class. Take a look at Kai's workSlate >page: > >http://www.geocities.com/~compcloset/ConvergentTechnologiesWorkSlate.htm Thanks for that info Doug, I picked a mint boxed WorkSlate up a few months ago at a fleamarket and haven't played with it much. I've got the doc set should anyone need any info. - Mike: dogas(a)leading.net

25 years, 11 months

← Newer
1
...
58
59
60
61
62
63
64
...
71
Older →

Jump to page:

2025

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

test-drb February 1999