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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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5th Jul 2011, 3:30 pm | #1 |
Triode
Join Date: Jul 2011
Location: Cambridgeshire
Posts: 43
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How to gain knowledge
Hi,
I'm a new member, with some very basic knowledge. I'm keen to try restoring a communications receiver such as the Yaesu FRG-7, but don't know enough about the electronics side of things. I wondered if anyone could advise me on the following ideas I have to get started: 1) Read "The Complete RF Technician's Handbook" (a second-hand copy of which I have ordered). 2) Buy/build test-gear (function generator, oscilloscope, multi-meter, capacitor tester etc) and use in conjunction with service data. I'm assuming this data would give expected measurements at various points in a circuit. I would welcome any advice. Many thanks........Mike |
5th Jul 2011, 3:56 pm | #2 |
Moderator
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Location: Ipswich, Suffolk, IP4, UK.
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Re: How to gain knowledge
Don't start by trying to restore a comms receiver. Start with a cheap valve woodie domestic radio.
You can find almost all faults in a radio with a multimeter. Forget about 'scopes, valve testers, function generators etc. for the time being. The best place to gain knowledge is here:- http://www.vintage-radio.com/repair-...ion/index.html
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
5th Jul 2011, 4:33 pm | #3 |
Nonode
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
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Re: How to gain knowledge
I would agree with Station X.
The FRG-7 is a Wadley loop triple conversion design and as such is a very complicated beastie. See if you can get a few cheap transistor radios from car boot sales etc to begin with. Al
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5th Jul 2011, 10:43 pm | #4 |
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Re: How to gain knowledge
Despite others saying 'don't buy a ''scope', get one, albeit true you don't need one to fix radios having one will enable you to SEE what is going on, extending your knowledge considerably. The only reason I can fix a radio with a 'damp finger' is because I first learnt how they work, a 'scope helped a lot here. Recently I got a Picoscope 2104, a PC based USB device, blooin' brilliant and for £125 does so much more than a standard 'scope, (frequency connter, spectrum analyser, pulse width meter etc.) one of those and an old proper AVO (£10..20 from eBay) and you have a pretty good test setup.
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5th Jul 2011, 10:52 pm | #5 | |
Retired Dormant Member
Join Date: Jun 2011
Location: Berkshire
Posts: 389
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Re: How to gain knowledge
Quote:
I agree a USB 'scope is a cheap way of getting some electronics 'eyes', maybe not much bandwidth but fine for a lot of basic audio stuff A decent multimeter (in my opinion) doesn't matter at this stage whether you get an old school analogue avo or a digi and a few decent tools , cutters, screwdrivers, soldering iron etc and then as suggested start with something broken and basic ...... or should that be basic and broken ? |
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5th Jul 2011, 10:56 pm | #6 |
Hexode
Join Date: Mar 2009
Location: Worthing, Sussex, UK.
Posts: 274
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Re: How to gain knowledge
I couldn't agree more... Much better to actually see what's going on with a scope. Any old cheap one is better than nothing. You're not going to have to make any accurate measurements with it.
Ging |
5th Jul 2011, 11:31 pm | #7 |
Rest in Peace
Join Date: Apr 2011
Location: Matlock, Derbyshire, UK.
Posts: 1,378
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Re: How to gain knowledge
I agree with Alistair D it is better to start with transistor radios, they do not bite.
An anlogue meter is good for looking at varying voltages and will measure the resistance of inductors. Many will measure transistor gains, A digital meter is good for accuracy which is useful for measuring transistor voltages. My digital meter goes bananas when measuring the resistance of inductors. A bought myself a present of a Peak LCR meter and a DCA semiconductor analyser. I use these often. I have an old 1A stabilised power supply using germanium transistors. This has output in steps of 0.1V from 0.1v to 39.9V. This is used to power transistor radios, charge batteries etc. Very big (19in rack) and heavy but still accurate to 0.1V. I have a scope which was scrapped when it ruined a very expensive test. I was allowed to take it home and the fault was a damaged mains fuse holder. I rarely use this. No-one has mentioned a solder sucker. |
5th Jul 2011, 11:57 pm | #8 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: How to gain knowledge
A 'scope if you can afford it if you are going for the long term (A picture says a thousand words)
A good second hand avo..good for real time intermittant V I @ R faults and loading AGC lines! A digital meter for realy fast go no go readings and really low ohms keep probes sharp. (I got a real cheap one) A basic RF signal generator for IF and expected signal frequencies. Solder sucker!! Decent soldering iron hand tools etc. Kettle. Progress accordingly. Servicing is pretty straight forward once you get the hang of it (Awaits flack) Good luck and have fun...think safety....always. Cheers. |
6th Jul 2011, 12:43 am | #9 | |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: How to gain knowledge
When I first read this Thread, my initial reaction was to disagree with Graham's comment - as below - about the desirability of a 'scope for a beginner. . . .
Quote:
As some of you may be aware, I am a fervent exponent of using a 'scope for fault finding work - but it's rarely that I dive in with a 'scope first: eyes, ears, and yes, the occasional sniff, can tell you quite a lot to start with. Knowledge of the item's history can be useful, too. (The obvious desirability of a circuit diagram is a given! ) Then a check on essential a.c. & d.c. voltages comes next. Of course, when, in due course, you acquire and then become proficient with a 'scope, and realise what a time (and headache) saver it can be, time can easily erase from the memory of how you used to 'get by' - and often with considerable success, too - before you owned a 'scope. There is also the distinct, and non too-obvious, advantage for the beginner - although he won't be aware of this at the time - that by being without a 'scope and armed with only a multimeter as a 'measuring tool', he will have to constantly go back to fundamentals to reason out cause and effect during fault diagnosis and remedy. It is this hard-won battle of keeping fundamental theory in the back of one's mind during all fault-finding procedures on any piece of equipment that, if not present, or if it is 'flaky', can lead to all sorts of problems. This is equally applicable to the raw beginner as it is to the time-served, skilled and accomplished professional. Having access to a 'scope at the early stages of one's learning curve is no substitute for hard-won experience. As is often said, there ain't no such thing as a free lunch. Al. |
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6th Jul 2011, 1:10 am | #10 |
Nonode
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
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Re: How to gain knowledge
To simplify this discussion, there is no substitute for experience and understanding of basic circuitry. Making an initial assesment of the fault symptoms will often tell which instrument is the best to start with. Having said that I was always of the opinion that if the DC conditions were not right then the AC conditions had even less chance of being OK. To back up my arguement, I fixed many a piece of equipment with a basic multimeter long before I had access to a 'scope.
Al
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6th Jul 2011, 8:38 am | #11 |
Hexode
Join Date: Aug 2007
Location: Bristol, UK.
Posts: 480
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Re: How to gain knowledge
IMV, the problem with buying a scope to learn electronics, is that you won't really understand how to use it properly. Better to start without, and buy one later on when you know more about what you know and do know (the known unknowns and unknown unknowns).
One good place to start, might be to build a kit of something that interests you and will be useful when complete, since that will get you some basic knowledge of construction techniques and components, and possibly electronic circuits and fault finding. |
6th Jul 2011, 9:04 am | #12 |
Retired Dormant Member
Join Date: Jun 2010
Location: Co. Limerick, Ireland.
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Re: How to gain knowledge
Free scope, spectrum analyser, signal generator, frequency counter etc, potentially up to 48KHz, certainly 22KHz.
I've used various versions. http://www.sillanumsoft.org/ Better than expensive PC software. Many built-in sound will do sampling 96KHz, 24bit and stereo. Some 192kHz. Most of the USB scopes only 8bits and Cheaper ones 200KHz. Rule of thumb, Choosing scope better than Sound i/o on PC. :: A good Analogue S/H 20MHz scope will let you view waveforms to 50MHz or 100MHz, it's accurate to 20MHz, thus still "works" at much higher frequency. Most do 5mV to 20V per division input. :: A USB or Digital Sampling scope can only "see" signals to 1/2 the sampling frequency, which is often 1/2 quoted on "dual mode". They are useful to 1/10th the channel sampling rate (1/20th master sampling on dual channel) is cheap and about 1/5th if more expensive to actually have idea of wave shape. Cheap USB scopes have very limited input range. Get a couple of DMMs. maybe one at £5 and one more expensive (but without graphics). My jaycar meter QM1538 has 10M Ohm input impedance (cheap meters are 1M Ohm) and has temperature probe, data cable to log to PC serial (or USB via adaptor), frequency to 10MHz, Capacitance as well as True RMS, volts, current and resistance. You really only need an AVO for valve gear (as schematics volts usually assume a 20k Ohm per volt AVO rather than DMM which will give high readings) and for over 250V (cheap meters die with blue flash on 750V range with 450V in). Also any RF upsets most DMM. An AVO, having no electronics, will not be affected. Last edited by neon indicator; 6th Jul 2011 at 9:11 am. |
6th Jul 2011, 9:50 am | #13 |
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
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Re: How to gain knowledge
I'm with Graham on this.
Despite the fact that 'scopes are cheap, and most of us who did the job for a living tended to use a 'scope for everything, learning to use one from scratch is another hurdle to overcome. Get a cheap fifties table radio (or three) and learn to fix it/them with a meter and maybe make yourself a signal injector. One thing at a time.
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6th Jul 2011, 10:51 am | #14 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: How to gain knowledge
Mmmm..To 'scope or not to 'scope...I suppose it depends on what type of equipment the gentleman wants to get interested in, for domestic radios maybe not so much but still would be a very valuble learning tool if finding it difficult to picture things in your head like we all do sometimes.
For old boat anchors / communications receivers I would suggest a 'scope is definately an asset ie: IF/Filter response, approximate frequency measurements...tracing hum!! etc etc also for component testing as mentioned in other threads on this forum, as a second real time DC/AC. monitor when you are trying to crack intermittant or temperature related faults,if you drift into tellys then there is no argument. I remember the little field service 'scopes, Cossor 1039 I think, they saved a lot of time out in the field...So time, that's another advantage, you will know instinctively when to get the 'scope out. Such a versatile peice of kit. Good luck with your venture. |
6th Jul 2011, 10:55 am | #15 |
Rest in Peace
Join Date: Apr 2011
Location: Matlock, Derbyshire, UK.
Posts: 1,378
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Re: How to gain knowledge
More comments.
Get a magic screwdriver (or a gullible assistant) to check whether you are going to get a shock. Use spectacles to protect eyes from solder flicks and exploding capacitors. My DMM didn't flash, just went fizz. |
6th Jul 2011, 9:53 pm | #16 | |
Retired Dormant Member
Join Date: Mar 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 1,587
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Re: How to gain knowledge
Quote:
Al and Graham I think are offering advice as 1 step at a time and learn well. In my youth ( looking back) I am amazed as to how much I could fix as Al says with my eyes , ears and a very cheap 20Kohm/volt multimeter. The scope often confims the fault rather than finds it. Regards Mike |
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6th Jul 2011, 10:40 pm | #17 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: How to gain knowledge
Hello Mike...Yes I get your point, I had to wait a couple of years before being "allowed" to use a 'scope in the workshop and even then it was a little begrudged, however when I ascended to the colour tv bench I had use of it all the time.
I, like a lot of members learned to sought things out with just an Avo and a bit of 'nouse in the earlier days which I have to say always stood me good. It's down to the individual I suppose. At the moment I do not have a 'scope, but it is next on the list, doing IF skirts without one is ok but a bit of a pain. I knocked up a scratch built PC 'scope in the eighties with a view to putting it to use in the workshop...all the engineers said it would never work..it did..well up to about 8 kc/s or maybe it was less!! All the best. Lawrence. |
10th Jul 2011, 12:30 am | #18 |
Heptode
Join Date: Oct 2007
Location: Birmingham, West Midlands, UK.
Posts: 615
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Re: How to gain knowledge
It all boils down to what knowledge / experience you have already, the test equipment is secondary. There is stuff out there cheap or free. eg I have a 200mc/s scope that has so many features on it I dont know what they all do. I paid £15 for it. As has been said, start simple, build a crystal set, mend a tranny and an old 50's valve radio. On this forum folks will fall over themselves to give advice as you can see but you will learn most by messing and experimenting to get a feel for how things work
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10th Jul 2011, 1:54 pm | #19 |
Retired Dormant Member
Join Date: Nov 2009
Location: Carmarthen, Wales, UK.
Posts: 79
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Re: How to gain knowledge
I've said it before to someone, it may seem obvious, but no matter what you want to start with, you need a reasonably spacious well lit table or bench to work at and a comfy chair. Someplace where you can leave things out then come back to them, using the kitchen / dining room table just won't cut it.
Equipmentwise, soldering iron with heavy stand and sponge, solder sucker, one analogue multimeter with easy to read scale, and one digital, (learn to use them). Usual selection of hand tools, (drivers pliers cutters etc). Signal generator and or injector is also useful, you'll find you can get a lot of learning with just that. Amateur radio books such as amateur radio techniques can be an educational read, and Scroggies Foundations of wireless and electronics. Lastly get some practice fixing up the older transistor radios from the pre chinese era, plenty available at boot markets and so on. hope this helps. |