The Tube Depot

The webpages are simple, quick to browse – to target a specific tube takes a couple of seconds. I really like this website! Not crammed with a load of rubbish which you don’t need or want to read about. Be warned though, tube amplifiers are addictive. I grew up in an era of valves, high voltages and output transformers. No doubt these amplifiers are exceptional value for money – back home if one can get a tube the price is up to 4 times the prices indicated in their catalogue.

I was in the merchant navy between 1980 and 1989 and our radio training very much involved triodes, tetrodes and pentodes although the stuff was reqgarded then already as being obsolete. (try getting 1500W PEP from only two transistors in the output stage then). Actually most people may not even be aware of the fact that they have a tube in their microwave oven – the magnetron. So don’t scoff then! The reality of the situation is that tube amplifiers sound different, are different and because of this lies their unique value. The Tube Depot certainly don’t sound as if they are targetting hobbyists in their 60s and 70s.  Although building tube amplifiers to a certain degree is easier to build than semiconductor units (only because they are high gain, voltage driven devices similar to FETs) be aware that you will be working with high voltages and youngsters should be supervised. That been said I think I’m going to get one for myself as a present at the end of the year. Cool

Note that Parts-Ring is not an affiliate of theTubeDepot – we advertise their wares because we believe that tubes should be given the respect they deserve, you can only love ’em and not be sent to the same mass grave as three year old computers.  

Tube Depot

Crank up the Volume [II]

continuation from [i]…

Big drivers are also prone to cone breakup if the frequency is not with the limits of the loudspeaker spec (inner part of the cone moves rapidly while the outer part can’t keep up because of mass, this can and will destroy the cone if not managed properly which of course manifests itself in terrible distortion. One needs to be totally deaf not to hear it).  And then you also have the power limits of most tweeters – they cannot handle the huge amplitudes needed to drive bass speakers.  Often listeners aren’t even aware that the tweeters have been damaged.
Filters: High Pass and Low Pass
So, the manufacturer of your loudspeaker enclosure uses a cross-over filter which uses capacitors and inductances (a capacitor displays reverse properties to that of an inductance i.e. the ‘resistance’ or reactance drops as the frequency rises).  So, by applying a capacitor in series to the high frequency driver (the tweeter) as the frequency rises more power is fed to this driver and by adding an inductance in series to the woofer (the low frequency driver), less power will be fed to the loudspeaker as the frequency goes up. Of course some loudspeaker enclosures carry more than two drivers, sometimes there is a squawker as well (mid range driver) – here the manufacturer would apply a filter comprising of both inductances and capacitors configured to allow only a certain range of frequencies through.

How good is this cross-over system?
Manufacturers have built some outstanding loudspeaker systems using the passive crossover network but they use extremely expensive components as opposed to the entry level sound systems one would get off the shelf.  These more expensive units are also very much designed around a specific speaker type, with specific dynamics in mind, so don’t fiddle.  In all likelihood you may think you have done a wonderful job by swapping bass drivers with a more expensive unit but in all probability if you haven’t consulted an audio engineer your final result may be worse.  Of course passive crossovers have one very important drawback – power loss.

In simplistic terms passive crossover networks are popular and the sound quality leveraged from even an entry level system is quite good but the enthusiast should be looking at an ‘active’ system – one which has crossover points that can be changed by the user, and an amplifier for each range of frequencies. The subwoofer is a classic case. Their cut-off frequency is very low but the entire system is designed around the loudspeaker driver.

Although I could drone on and on about this subject, readers do have access to some excellent reading material on the web with regards to filters, one of course is

Next article: Bipolars versus MOS devices (and radio valves/tubes as well). – please note these articles aren’t meant for the hard-core electronics engineer.  In time we are hoping that readers will start submitting their own ideas and gripes on to the forum about the various topics covered.

DIY Electronics

The downside to modern electronics in this quick-fix age is that sometimes it’s so much cheaper to buy a readily built item as opposed to building one yourself. But don’t kid yourself, 90% of the fun is building your own – possible from a kit or from scratch. I’m really amazed at the amount of knowledge out there – so many youngester designing digital kit without formal training, often just very passionate people.

The most popular construction kits in my heyday in the 70’s and early 80’s were always audio, be it disco, power amplifiers, pre-amplifiers or mixers and in second place were light chasers and radio. Actually the most fun someone can have is to pick up a book about audio design and build your own audio amplifier from scratch. Radio valves (or tubes) held a special interest because of the simplicity and danger to a youngster. There is a lot of fun out there still to be had because now of the interfacing between an affordable laptop and your sound system through audio jacks and control through USB.

pcs banner

There are also brilliant magazines out there – albeit mostly British which cover electronics as a hobby or the professional sector but with the internet on tap now 24/7 we should not forget about the manufacturers – they supply a host of information and indeed in most cases supply the entire details of a project that one may be building due to the specific chip that they manufacture.

Lastly, the age of driving backwards and forwards to pick up components from one vendor to the next is also over. This was always a problem. I remember building a power MOSFET amplifier where the only supplier of a specific Hitachi device was 1600 Km away.  So you have the boards, you have the components except the most important – in actual fact all the components could have been purchased from the last vendor. I don’t kid myself when it comes down to building a project, developing countries don’t have the parts and more often than not you may end up buying parts which are inferior in spec (or just don’t work) to the designed requirement. A classic case was building a quasi-comp. amplifier which used 2N3055s. These kept on popping every time we switched on the P.A. but once switching to Toshiba transistors there wasn’t a problem.  The previous were manufacturerd by a no-name company out in Asia somewhere. When one considers the time wastage (and money) in trying to get this project off the ground it’s best to go back to the basics and with electronics it’s no different – know your supplier and that the components are of good grade. 

pcimax 2007+ animated

The company advertised in this page do a great job of supplying enthusiasts with top quality components as well as affordable radio equipment. It must be noted that in a lot of countries it it is NOT legal to have any device which can transmit over a certain power or within a certain frequency spectrum. Contact your national broadcasting authority to get details before making any purchases.

Crank up the Volume [I]

Not being in the same class as the famous or infamous Jeremy Clarkson, of whichcardoIdrivetoday fame I’ll try to elaborate by saying that I’m a serious listener but not so keen reviewer – all manufacturers bring out a sound system which can beat the next manufacturer’s easily but never the listener. Who cares if you the have Philips Dolby XX Minus 5 or the lastest Marantz ZX 55 Spitfire – even more so, “my husband has the latest Wharfedale 22″ Incredibles and the biceps of Arnie” – before buying a sound system, don’t go by the ad, drive it! If you are prepared to pay serious money for a sound system don’t even bother about listening to your mate, the salesman – listen,listen and listen again. Oft been said – take your favourite DVD or CD with you and listen to it. Be careful of the sound room factor though – do they have one? If not you are in the wrong place. Do they have one and is it similar to yours? If not get them to test it at your home.  This doesn’t work with entry level systems by the way.  You may be in for a drive by shooting with this idea in mind.

Well today we are actually going to be talking about something different – the amplifier.  I’m going to mention only two words in today’s exercise: 

Ceiling and Match.

My definition of amplifier ceiling is the power that your amplifier can reproduce a level of sound that is comfortable to the ear but yet when there is a transient – the reproduction will be clear and give you palpitations, night sweat, raised blood pressure and humping a hollywood star. An amplifier must always have room for plenty more – unfortunately the computer home theatre systems that put out 200PMPO aren’t going to cut the grade. I have heard and read about the different ‘new fangled methods’ that one derives the power output of an amplifier to get to PMPO but most of them are thumb sucked or utter bullls**t – go with the tried and trusted RMS power delivered into a load of such and such. To cut to the chase there are only three ways – continuous power, RMS power (a colleague once mentioned that he overheard a sale person saying that it meant “Real Mean Sound”) and lastly, a good old fashioned way of testing – pick the damned thing up***.  If it’s heavy, you’re half way there – as long as someone hasn’t weighed it down with a lead weight inside.  That’s another story entirely.

1) Continuous power/RMS. OK, let’s look at the following reasoning:  Your home theatre amplifer can deliver 600 Watts RMS.  Is this all channels driven or only one mulitplied by the amount of channels the amplifier has? The specifications should state whether simultaneously or not.  Because your home theatre is not designed to reproduce all inputs at the same level at the same time I qualify this as being reasonable; the home theatre system is not designed to put out 600W RMS continuously, which gets to point 2)
2) I feel so heavy now. The amplifier should be able to sustain the output power continuously…. which means what?  Power transformers and power supplies are the order of the day. Regulated power supplies, big, rugged transformers and reservoir capacitors the size of the wart on your nose. Hey guys, get a life! A good power supply is one of the most important parts to your amplifier.  The ceiling (mentioned in column C, paragraph Z, agent X) relies on this more than anything.  A power supply which drops it’s output rail voltage will affect the output – and the bass is going to be so severely affected you’d want to throw it out the door after one session with Pink Floyd, or with Michael Jackson’s Beat It. There’s a fairly well known formula for calculating power of an amplifer; note though this is with a non-bridged format power amplifier – we’ll get to that later:  Vcc(squared)/8RL; power rail voltage to the power devices divided by 8 times the load resistance.  See what a difference your amplifier would make if the supply voltage fluctuates? The voltage drops, the potential power output drops – and if it drops to a degree where there is mains ripple on the supply rails, well then you lose the race. In fact so many amplifiers distort so badly when hitting the upper limits that you won’t be worried about the bass.
3) Your suspension is damping out my dear. Good loudspeakers are meant to be driven – don’t fool youself that you bought the best sound system to impress your wife. My wife hates listening to loud music unless it’s Robbie Williams and I know she isn’t listening to the music. Well, unfortunately for you guys out there wanting to hear about the damping factor – a very crucial part to the dynamics of your sound system, and here we are in fact only going to be covering the impedance of the loudspeaker – the damping factor comes in a little bit later although what we cover here is all relevant.  I deliberately covered the aspect of power output first and then the weight. (cunningly disguising the power supply as being the main topic). What about loudspeaker impedance? What is impedance firstly? Simply put this is the resistance measured when an alternating current is applied to …. a load in this case i.e. your loudspeaker. In electronics we call this reactance. A loudspeaker has a magnet and a voice coil, bingo – you have it! The voice coil is an inductance which has a direct current resistance – but applying an alternating current to it the ‘resistance’ rises as the frequency increases. And sadly, as Whitney Houston hits the high registers so unfortunately your loudspeaker impedance start to rise. Remember that little formula we mentioned earlier on – that one with the square of the supply rail voltage divided by that other stuff…. well now you can see that as the frequency goes up the loudspeaker volume starts dropping because the ‘resistance’ gets higher. Or does it?  Ummm, now something intersting starts to happen between that crossover network and your hearing.   Wait for the next article.

The Lounge Lizard

***I’d be weary of buying something like an audio amplifier with a switched mode power supply – it will be a nightmare to fix and secondly this article is going to lead to you – yeah, you, building your own high performance amplifier and SMPS will not be covered.   We will show you how to re-design a computer power supply to deliver a symmetrical +/- 40V at 5 amps. What a bonus.

Part II

Throwaway Parts

people have to open up things to see how they work. I had an old Telefunken tv in for repairs many years ago which had a 40W light bulb in it which was used to drive out moisture and prevent the light touch channel selector panel from dancing around when first switched on – yep, if they had cleaned the panel it would have been OK too but 1 000 kudos to this guy – he didn’t get the solution on Google. He used a bit of initiative. The next time I made a house call the complaint was that the tv has stopped working. Ummm, this time someone has told him he could economise on electricity by driving the light bulb by wrapping a couple of turns on the LOP-T.  (I believe the reasoning here was that the tv would power the bulb Cool).  Good one there…

The older television receivers were always a bastard to repair – the chances of a secondary failure within a month or two was always high (hey, these sets were up to 18 years of age) and the downtime to fix it – mainly owned by pensioners who could not see the merit of replacing a set when they were going to die soon anyway Surprised used to confuse me – used to be more of a menace than good practice. Yes, I used to give a guarantee of 90 days on the workmanship but an 80 year old to buy a new set? No ways!

Modern computers are a different story, or is it?  Hardware related issues are sorted out within 20 minutes – slap a new memory module in and off you go. And you make 100U$ on the repair because the registry is corrupt. What a way to earn money – watch XP load itself while you earn a dollar an hour sucking on coffee.  Hang on, is it that easy? Of course not. Recently I had my dad’s PC in for a repair. Nothing much wrong with it – could not boot. As luck would have it I work for a company which sells hardware – had one of the guys check the board out (an old 478) and alas it had failed. Anyhow, the decision was that I would not put another 478 unit in to save some money – got another 478 board from kin and set to work. The board was an old Intel la Crosse which was way too big to fit into the old man’s chassis – what to do, what to do? Exchanged the board from a system I had and in the process burnt out two flash drives. Yep, the header of my chassis was not matched to the Intel board which I had claimed. (for ethical reasons no manufacturer names shall be mentioned). The system for my dad had other issues a) the hard drive would not load XP – he used to have 98SE but could not get into device manager except under safe mode and would freeze normally, even with most of the drivers disabled – something strange going on here? b) XP essentially told me there was something wrong with the drive. You guys have all seen this so I won’t elaborate.  Luckily I had another drive which was given me with the faulty system – blow me down same problem. Both drives with MBR problem. It was at this stage I heard that my young nephew – a computer genius in the making had been doing some fine tuning on this system.  So with a power supply which had to fixed, no biggie – only the fan, MBR issues, reload of software – problems with my own PC because of the header problem and subsequent XP activation (how can I activate XP without a LAN driver – thanks to Toshiba notebook I sorted that one out) blah blah blah I had my dad’s system running in about 6 hours.

The process above is no biggie – suck on a couple of beers, try different permutations and eventually you’ll get it right – but the problem here is the time taken to administer the repair. 6 Hours – that’s quite a bit of money if you had to equate in business terms.  Where I work we distribute a new PC with XP home on it for about 450U$ – with a monitor. The lesson to be learnt here is that fixing old computers and fixing old television receivers leads to the same conclusion:

Buy – don’t fix. (salesmen/women love thisMoney mouth)

A new entry level OEM system can carry a price tag of around 450U$ (actually lets talk local currency of about R3K) and it carries a carry in warranty of between 12months to 3 years – why worry to fix?

A 51cm entry level television receiver costs 200U$ – why bother to fix? 

Obsolescent Products

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Thank you for your support.

The Reader knows Best, Teacher

besides “a calculated use of violence, or the threat thereof against people or persons to attain certain goals” – something that most people living in South Africa are well familiar with.  In the dark years, living in South Africa one could expect and not be disappointed to find your education, transport, health and your general security being compromised. I’m trying to figure out something.  Have things changed that much?  Has South Africa really moved forwards? Cosatu [Congress of South African Trade Unions] is now blackmailing the government, the country, the people.  I’m all for fairness but things have become so backward internationally that one wonders where Maggie Thatcher is now that we need her. Let’s not look just at South Africa. Worldwide this has become a joke of substantial proportions. We all work with a lot of people from all races, nationalities, creed, colour and religions – whether it be in your own little empire, for a boss, corporate or otherwise and one thing sticks out like a sore thumb:  most people are getting tired of this.  To be more specific – the reality is that we have become so weak that we take the path of least resistance.

I’m going to discuss something which has worried me for some time. The a+b phenomena. In the last year I have interviewed a minimum of 30 people that have taken mathematics at school and they say that they loved the subject. I ask them “What is a+b then?”. To date not one, yes 0% have been able to give me the propler answer. Simply put, can I add an apple and a pear? Another question posed to people that took chemistry at school and found it to be their bestest, much likest subject: “What is NaCl?” Again a resounding zero to all contestants. These people are out there looking for jobs, want big money and they too, (yes they will) can strike when they feel that they are earning too little. Output zero. Skills zero. 

I find this odd.  What could be the problem. I’d like to that think a lot of the interviewees were just plain thicko but we are not taught to think this. Every now and again we have someone that is so sharp, so bright, so cunning, so clever that cannot believe our good fortune. But you know what – they are all just well read. Good parenting. Good teachers. My favourite person in South Africa is Barry Ronge.  Huh? Yes, here we have someone whom has a passion for the English language. Like I expect my French teacher to be. The question I ask myself is what has changed?  My science teacher had a passion for the sciences. My accountancy teacher told us not to trust science. It changes. Accountancy doesn’t. A debit remains a debit and a one remains a one. They were all correct.  It was a passion they had and the better they were at teaching their subject the more followers they had.  I love accountancy, maths, science etc, etc. I like learning. I try not to be conceitedKiss because I know my short-comingsEmbarassed, I was bad at English and worse still at my second language although both teachers were excellent. But I can hopefully understand what I read because …. I just read. If I don’t know I look it up. Like Barry. But I’m not as bright as Barry and never will be.  But I bet you he cannot change a spark-plug.

I’d really love all the teachers out there to start telling their kids to start reading. I also want all the teachers out there to start listening to what Mark Shuttleworth has to say and explore all avenues of science with their kids. To me Mark is possibly one of South Africa’s great mentors. Not just Madiba.
If teachers don’t get support, neither do the kids. “My Kingdom for a Horse.”

Guys, girls – in September 2009, as I write this article you need to start showing a damned sight more respect to your teacher, your class-mates and your studies. From what I have seen at an international level we are nurturing an empire of morons.  Have an interest, read a book and get off the ganja. If you want to go on the internet go to ‘How Stuff Works’. Go to ‘Popular Mechanics’, go to ‘Microsoft’, to Wiki, wherever – but start reading and start showing an interest.

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