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Old 6th Nov 2017, 12:49 am   #61
Skywave
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Arrow Re: The perils of homebrewing equipment

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Originally Posted by Radio Wrangler View Post
That's the danger. Someone builds something and it works so they think it's OK to publish.

Sometimes, to read a magazine article and to be able to decide whether it's OK to build takes as much knowledge as designing your own thing properly in the first place.
It's survivable for hardened constructors, but it can damage the confidence of beginners.

David
Indeed: building a one-off for your own personal use is one thing, but then publishing it as a 'proven design' is something else: to my mind, at that stage, it hasn't been 'proven', although 'proof of concept' has been established. It's been my experience (many years in Gov't. R & D) that after a professional design has progressed from the bread-board to one prototype, that one is thoroughly tested: the general idea being how easy is it to cause it to malfunction. Next, several prototypes are built - and subjected to the same rigorous testing procedure.

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.

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Old 6th Nov 2017, 3:21 am   #62
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Default 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.
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Old 6th Nov 2017, 4:55 am   #63
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Default 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
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Old 6th Nov 2017, 10:39 am   #64
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Default 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.

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Old 6th Nov 2017, 12:36 pm   #65
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Default 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.
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Old 6th Nov 2017, 2:54 pm   #66
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Default 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
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Old 6th Nov 2017, 3:45 pm   #67
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Default Re: The perils of homebrewing equipment

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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.
G3WPO was the callsign of Tony Bailey, who was for a time quite prolific in his output of designs and kits. He had a hand in the Omega, with Frank Ogden, G3JST. Tony is still around. He hasn't bothered with amateur radio for almost three decades (since 1989), but occasionally people track him down and ask for information regarding some item or another that Tony designed. He replies to say that he can't help - he has no copies of articles or parts:

http://www.wpocomms.co.uk/g3wpo.php
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Old 6th Nov 2017, 10:45 pm   #68
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Default 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
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Old 8th Nov 2017, 11:53 pm   #69
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Default 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".
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Old 9th Nov 2017, 12:10 am   #70
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Default 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
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Old 9th Nov 2017, 12:58 am   #71
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Default 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!
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Old 9th Nov 2017, 3:07 am   #72
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Default Re: The perils of homebrewing equipment

Yep, been there done that once too many times now.
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Old 9th Nov 2017, 3:39 pm   #73
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Default 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...
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Old 9th Nov 2017, 8:01 pm   #74
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Default 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...
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Old 11th Nov 2017, 10:45 am   #75
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Default 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.
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Old 11th Nov 2017, 11:31 am   #76
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Default 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!
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Old 11th Nov 2017, 4:41 pm   #77
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Exclamation 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.
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Old 11th Nov 2017, 5:38 pm   #78
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Default 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.
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Old 11th Nov 2017, 7:19 pm   #79
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Default 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
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Old 12th Nov 2017, 9:16 am   #80
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Default Re: The perils of homebrewing equipment

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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
That's called "fail-safe"
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