|
Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
|
Thread Tools |
6th Nov 2017, 12:49 am | #61 | |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: The perils of homebrewing equipment
Quote:
As for published designs from sources which have acquired an air of 'professionalism', which, for the keen beginner-constructor, results in failure, I was once there (and to a certain extent, still am ) Such a source that springs to mind are some of the designs in the R.S.G.B Handbooks that have been published over the years. Now that I am much older and have learnt much more during the intervening years, I can now see some of the mistakes that exist in such designs. Al. |
|
6th Nov 2017, 3:21 am | #62 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: The perils of homebrewing equipment
Though I think once the design gets past a certain level of complexity even professionally designed circuits can contain bugs.
Consider Atari's original Arcade Pong of 66 TTL IC's, it contained 6 bugs. One related to a timing error that occurred if some IC's (still in spec) had a short propagation delay. Another was a "logic race" that the game could get trapped in, and other bugs were omissions to do things like gate video signals out of blanking. Yet despite these things, it was an amazing commercial success. It is an example of how some flaws, if minor enough can be tolerated in circuit designs. I have come to accept that if I build any circuit someone else has designed, even supposed proven designs, there could be an issue to resolve. I would expect that if anyone built any of my designs, they should be prepared to accept that an issue that I did not experience could crop up in their version of it. Always be ready for anything in newly built circuits. One I had recently was a 3.3V regulator oscillating, because the 10uF 35V Tantalum capacitor I used had a higher ESR than the 10uF 16V one the designer used. |
6th Nov 2017, 4:55 am | #63 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,924
|
Re: The perils of homebrewing equipment
Thinking in particular about constructional projects published back in the 1960's in PW, mainly using valves, just occasionally they would publish a follow-up article with some corrections or suggestions about some problem in the original. However, there was one project that seemed to be almost cursed and it seemed that lots of people had built this and many had reason to complain. It was the "Explorer" project, which was transistor VHF super-regen which seemed to offer a relatively easy way to explore the realms of VHF away from the FM broadcast band. I'm sure many on here will recal it.
Published in the late 60's(?), it was a time when transistors were expensive, not well understood and virtually impossible to test for amateurs. I seem to recal that one of the problems was that the transistors used in the prototype had either become unobtainable or had changed spec or some such problem. PW had to publish at least one follow up article to try and sort out what seemed like the worst mess they'd ever had. In a "senior moment" a couple of days ago, I briefly shorted the output of a MOSFET module and of course it died! Where I'm heading here is that there are days when I consider whether I should limit myself entirely to working with valves. I don't recal ever building a valved project which didn't work ...eventually. I don't recall ever destroying a valve accidentally. Certainly, it's at these times when I see why some people are so keen to concentrate largely on restoring vintage radios rather than constructing homebrews. B
__________________
Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
6th Nov 2017, 10:39 am | #64 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
|
Re: The perils of homebrewing equipment
Hi.
Yes, PW did have it's fair share of problems which were often addressed in follow-ups and by correspondents contributions. I remember one particular project, a transistor tester published in the late 1960s, it was riddled with errors on the board layout, circuit diagram and components list. I think I counted around 8 or more mistakes. What was disappointing in this case, there were no follow-up corrections or not even a mention in the readers' letters column. Perhaps it was quietly dropped to avoid any embarrassment. From memory, Radio Constructor had far less problems with errors in their publications. Regards Symon. |
6th Nov 2017, 12:36 pm | #65 |
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,034
|
Re: The perils of homebrewing equipment
I recall (sometime in the 80's) a major constructional article in several parts for a complete HF transceiver. The magazine would have been either 'Ham Radio Today'(?) or 'Amateur Radio'. Everything was going swimmingly until it was time to do the PA, which came in two versions - a QRP version rated at 10w PEP and a bigger one which could do 100w.
One version - I think it was the low power one - had stability problems and would see off its output transistors. Month after month we were promised it would be sorted out and published but ISTR it just sort of fizzled out. Then there was the HF linear amplifier which had no mains transformer, just running directly from the mains into a voltage quadrupler. Ooooh, the horror. I think it caused quite a lot of discussion at the time. Sorry if that one is a bit off-topic.
__________________
Andy G1HBE. |
6th Nov 2017, 2:54 pm | #66 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
|
Re: The perils of homebrewing equipment
The first one was the Omega transceiver project in the UK "Ham Radio" magazine. I think it was Bill Pohl G3WPO and possibly Frank Ogden behind it. At least they knew of the problem and were honest about it and didn't publish something they had doubts over. Chris Honey did a good QRP PA and I'm trying to remember where it got published. I built one and hung it on the end of a Redifon GK203N.
The high power amp with non-isoleted multiplied mains was, I think, the Mr Webb who also did the CobWebb antenna. The whole thing floated, isolated by inoput and output RF transformers. Designed for low weight for DXpeditioning. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
6th Nov 2017, 3:45 pm | #67 | |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
|
Re: The perils of homebrewing equipment
Quote:
http://www.wpocomms.co.uk/g3wpo.php
__________________
David. BVWS Member. G-QRP Club member 1339. |
|
6th Nov 2017, 10:45 pm | #68 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
|
Re: The perils of homebrewing equipment
Hi Gents, I believe Elektor has learnt from others mistakes.
They normally supply all authors with a PCB of their design for them to debug and correct as necessary (just like commercial practice). They are normally pretty good at publishing the odd correction the following month. They also proof read and check your English as well! Ed |
8th Nov 2017, 11:53 pm | #69 |
Octode
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,782
|
Re: The perils of homebrewing equipment
Since my retirement, my home construction has gone "ballistic" in as much as being single, home maintenance, in check....allows me a lot of free time to "play electronics". There are not many days that I am not in the workshop at some part of the day. Without some of the learned members of this forum, I would struggle at times and to that end I thank you. As some of you know, I prefer to build, rather than buy, being a "yorkshire person", but saying that, the number of "prototypes", pcb artworks and boards, probably cost more that the commercial item, but its FUN, keeps the days from being boring, I hate gardening with a vengeance, so... self build for me, everytime "mostly".
__________________
Should get out more. Regards Wendy G8BZY |
9th Nov 2017, 12:10 am | #70 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
|
Re: The perils of homebrewing equipment
Tony Bailey... ah, yes, it comes back! Thanks, David, the memory cells needed a thump.
It was a very interesting magazine in that period. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
9th Nov 2017, 12:58 am | #71 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
|
Re: The perils of homebrewing equipment
Well I did a silly today. I assumed that the line on a tantalum SMD capacitor was the negative lead. Not until it departed with an incendiary salute did I work out that isn't the case!
|
9th Nov 2017, 3:07 am | #72 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
|
Re: The perils of homebrewing equipment
Yep, been there done that once too many times now.
|
9th Nov 2017, 3:39 pm | #73 |
Rest in Peace
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 2,234
|
Re: The perils of homebrewing equipment
The thing is with me that I presume because I have been in the trade for quite a few years now I can get away with things like that. I am constantly reminded that this is definitely not the case. And I still can't get my head around 5 band resistor colour codes. But that has been discussed extensively on the forum already...
Alan. |
9th Nov 2017, 8:01 pm | #74 |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
|
Re: The perils of homebrewing equipment
Some circuits are all about the quality of the mechanical layout and construction. It doesn't matter how many times it's been made before, it's the next one that counts. It took me quite a while to acquire the skill to make very short busbars and passive component connections with tiny leads, right on the pins of the devices, to reduce ringing in high frequency, high power MOSFET circuits.
My best work was, for a time, nowhere near good enough. Ironically, for a while, I was afraid of destroying devices by soldering close to the encapsulation, but it was the inductive spikes from even tiny lead lengths that caused the damage instead. It took a lot of practice to get this right. No amount of armchair theorising can replace practice sometimes, and it's not enough to just observe models of best practice. Same with gate transformers, they used to be all over the place...
__________________
Al |
11th Nov 2017, 10:45 am | #75 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
|
Re: The perils of homebrewing equipment
Being 'too delicate' can be a problem: some RF gear I was involved with a few decades back was 'modular' - you ordered a chassis, a low-power PSU, the frequency-synthesizer, the receiver, the transmitter, the modem, the data interface, the high-power PSU.
Some of it came as individual PCBs. One of our guys saw the price being charged for these and decided he could clone them more cheaply in the lab, working during quiet periods. He spent ages trying, but could never get the synth stable. I had a look at it, tapped it in a couple of crucial places while watching the frequency-counter, tightened a few screws, and happiness reigned! The problem was that the PCB manufacturer had applied the usual green conformal coating, but had put it over the holes on the 'ground' side of the PCB where the screening-can for the TCXO module was screwed [the TCXO being a rather large brass cube held to the main PCB with six screws]. The screws weren't being tightened enough to make the star-washers bite through the coating-that-should-not-have-been-there. "I know how much those TCXO modules cost - I didn't want to overtighten the mounting screws and strip the threads!" being the summary of about a week's wasted effort. |
11th Nov 2017, 11:31 am | #76 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
|
Re: The perils of homebrewing equipment
That doesn’t surprise me actually. It’s amazing how this is actually factored into the design. Many an ill or fuzzy trace can be cured in Tektronix scopes by tightening the screws up on the attenuators and vertical amps!
|
11th Nov 2017, 4:41 pm | #77 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: The perils of homebrewing equipment
The one area of 'home-brewing' that experience has taught me to be very careful with is the designing and subsequent testing of ccts. that use medium-power type transistors (such as 2N5416; 2N3439; MJE 340 / 350) with H.V. power supplies (300 to 350 v.d.c.) One slip - and pop! Exit all semi-conductor junctions.
Al. |
11th Nov 2017, 5:38 pm | #78 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
|
Re: The perils of homebrewing equipment
Another peril: some of the very early memory-chips required several supply-voltages, and at power-up these voltages had to be applied in a particular order or the chip was destroyed.
I got hold of a secondhand board using such chips, and over several days re-engineered it to work as an additional 4K of RAM for my Elektor "Junior" computer. Unfortunately I was unaware at the time of the requirement for power-supply sequencing so the first time I powered it up things did not go well. In the end I used a bunch of 2102 chips instead. |
11th Nov 2017, 7:19 pm | #79 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
|
Re: The perils of homebrewing equipment
I remember some of those awful ones that needed -8v for some reason, probably to stop the implicit substrate diodes from conducting. Think it was an early 8080.
Had another mishap today. Turns out SMD resistors are actually pretty amazing in overload scenarios. I had some 0805’s burning a watt each. That was until they fell off the board |
12th Nov 2017, 9:16 am | #80 | |
Nonode
Join Date: Aug 2010
Location: Resolfen, Wales; and Bristol, England
Posts: 2,588
|
Re: The perils of homebrewing equipment
Quote:
__________________
Richard Index: recursive loop: see recursive loop |
|