a.palfreyman
pfm Member
Yes, wot Shadders said.
AP
Amplifier repair courses?
- Thread starter rescuest3ve
- Start date
-
- Tags
- courses
AP
Millennium
pfm Member
I know a guy near Wimbledon who fixes amps (hello there if you're reading David) and I'm wondering if he might be willing to take me through some basics for an afternoon or two.
However he is really busy and I don't know if I want to impose. Anything in London to learn some repair skills for us? Must be a useful life skill!
However he is really busy and I don't know if I want to impose. Anything in London to learn some repair skills for us? Must be a useful life skill!
Jim Audiomisc
pfm Member
Two potential snags with the above.
1) Being good as someone who can repair and/or design and build doesn't mean someone can teach well.
2) The big responsibility when it comes to teaching a subject like practical electronics is the safety aspect. If you teach someone you take on responsibility for this, and if something goes wrong the injured student - or their family/lawyers or police may come knocking on the door of the teacher.
Jim Audiomisc
pfm Member
It's the soldering iron that worries us!... :-]
Tony L
Administrator
I’ve actually been doing that so long now I’m very neat, e.g. I’ve swapped some chips on my BBC B and you would never be able to spot my work from the factory. I learned which end to hold way back when I started playing in bands as a teenager as cheap jack leads kept breaking etc, so I have just slowly built up from there. I’ve not tried any surface mount stuff yet, but I’m fine with pretty much everything else.
The thing I don’t have is any actual electronics knowledge. I know what a resistor, capacitor, transformer, diode or whatever does in theory, but beyond that I struggle to get more than a general gist from a circuit diagram. I’ve absolutely no interest in designing or modifying anything, so really all I want to build up to is to be able to service existing well documented stuff a little better. I’m hoping to learn to use the scope to better understand amplifier bias, distortion etc, help fault-find old 8 bit computers etc (check I/O to various chip legs etc).
PS Its a Hameg HM303-6 (this one). I’m sure I’ve overpaid somewhat as some folk seem able to land lovely scopes for £50 or even find them in skips, but it looks in stunning condition, isn’t too old (Dec 03), and it clearly works. Its a nice simple scope too, so I already know what the various functions do (I use a scope at the museum on the SSEM so do have a little knowledge already). Quite a few of the YouTube retro computer community seem to use the same or very similar models so it should do everything I would ever need and more.
This site contains affiliate links for which pink fish media may be compensated.
martin clark
pinko bodger
@Tony L
In that case you'll be wanting to look at Tektronix' classic application note 'XYZs of Oscilloscopes'
I think it's the best primer on using a 'scope there is - assumes little knowledge and a model of clarity in technical writing in explaining how to learn to exploit what even a simple 'scope' can deliver. You can download the current version here:
https://www.tek.com/document/primer/xyzs-oscilloscopes-primer
In that case you'll be wanting to look at Tektronix' classic application note 'XYZs of Oscilloscopes'
I think it's the best primer on using a 'scope there is - assumes little knowledge and a model of clarity in technical writing in explaining how to learn to exploit what even a simple 'scope' can deliver. You can download the current version here:
https://www.tek.com/document/primer/xyzs-oscilloscopes-primer
Jim Audiomisc
pfm Member
Scopes like the Hameg can be very useful. Do you also have some x10 probes?
However if you're interested in aspects like audio distortion, etc, there may well be a good program you can use on a computer via a USB ADC. I've written an example for Linux that does a scope + FFT display, but there will be many others.
Tony L
Administrator
Thankfully it comes with a new pair of switchable probes, which is one less expense. Comes with a set of multimeter probes too for the component test function, though I’m not short of those. I just hope it lands safely from Germany, though the seller is an oscilloscope specialist with 100% feedback and a lot of it so it should be ok. If not I have eBay buyer protection!
Arkless Electronics
Trade: Amp design and repairs.
+1 to that! All the Tek technical writing and service manuals were a lesson in just how it should be done! Even had little cartoons in some of them!
Arkless Electronics
Trade: Amp design and repairs.
Agreed but to me the single biggest problem is the "a little bit of knowledge is a dangerous thing" part! Just because the innards of amp A look somewhat like those of amp B does not mean that what you learned on amp A is in any way applicable to amp B! It might be... but it very well might not be as well and the over confidence from working on amp A could lead to someone who would likely have never touched such a thing previously thinking they can also work on amp B... with serious consequences of at least an amp which is now toast, maybe taking out speakers with it, and at worse a house fire!
Tony L
Administrator
Got my scope! Astonishingly it survived the utter bell-end from Hermes not ringing the door bell, not using the door knocker, and actually deciding to throw it over the back wall into the yard where it landed on a pile of bricks. It just reinforces my view that Hermes really are the worst of the lot and by some considerable margin. They really do employ some useless brainless shit! At least the dick head threw it in my yard, not the neighbours as has happened before.
Anyway, the seller packed it very well and it is surprisingly light so survived without any evidence of damage inside or out (it actually looks pretty much new). I get the impression this is a very late-period CRT scope, it certainly weighs but a fraction of the ‘80s Tektronics we use at the museum, and there is very little inside with a switch-mode PSU and a lot of surface mount stuff. No sign of bulging or leaky caps and all knobs seem to work ok as far as I can tell. Yay! I have a scope!
Arkless Electronics
Trade: Amp design and repairs.
Got my scope! Astonishingly it survived the utter bell-end from Hermes not ringing the door bell, not using the door knocker, and actually deciding to throw it over the back wall into the yard where it landed on a pile of bricks. It just reinforces my view that Hermes really are the worst of the lot and by some considerable margin. They really do employ some useless brainless shit! At least the dick head threw it in my yard, not the neighbours as has happened before.
Anyway, the seller packed it very well and it is surprisingly light so survived without any evidence of damage inside or out (it actually looks pretty much new). I get the impression this is a very late-period CRT scope, it certainly weighs but a fraction of the ‘80s Tektronics we use at the museum, and there is very little inside with a switch-mode PSU and a lot of surface mount stuff. No sign of bulging or leaky caps and all knobs seem to work ok as far as I can tell. Yay! I have a scope!
Those are negatives! One of my Teks is from their last CRT range and weighs nowt, has SMPS etc... a 2215. It doesn't deserve the Tektronix name.
Lucky it survived the inept courier there...
More than enough bandwidth for anything you are likely to do there and it looks a minter.
I have the digital storage version of the 20MHz Hameg and another for spares but I've probably only used it for half an hour in ten years!
If I ever make a bulk purchase of round tuits I'd like to sort out my ancient Cossor CDU150 scope.. a beast! NOS from MOD when I got and I used it for about 10 years, dates from about 1970, huge, heavy and has every facility you could possibly desire... Unfortunately a major mistake they made IMO was to not fit a cooling fan... the outer case and front panel reach maybe 45-50C in use and I always thought "this does not bode well for all the electrolytics in there".... I'm amazed it worked for 10 years of daily use in fact! It's just a lovely thing from a certain age really but it does work very well, with high specs etc when going. 35MHz bandwidth, delayed sweep, variable hold-off.. it's got all the "bells and whistles"!
Tony L
Administrator
Theoretically I agree, and I did think very long and hard about what to go for. I’d love a real high-end vintage Tek or something similar (a big valve one!) but I clearly don’t have the skillset to fix or restore an oscilloscope. My main priority at this point was something perfectly working so I can learn. I also wanted an analogue CRT scope as whilst I recognise the advantages of modern high-bandwidth digital scopes they are just too menu-driven and filled with way too many options for a beginner IMO. A while back three of us at the museum (the other two being competent retired electronics engineers) really struggled to figure out some Chinese LCD storage scope someone brought in, just baffling degrees of complexity with menus and settings everywhere. As such I wanted a basic late-period CRT scope in as close to NOS condition as I could find and this fits the bill pretty well I suspect. It should be a good ‘starter scope’ and still fast enough to work on old 8 bit computers etc.
Arkless Electronics
Trade: Amp design and repairs.
I really can't stand digital LCD screen etc scopes... the "picture" is crap compared to the old analogue ones and when trying to measure low level signals some sort of "digital noise" makes the trace about 4mm thick and fuzzy...
At a job working on money no object MOD stuff I nearly rejected as faulty a batch of £20K Agilent scopes after trying a couple and seeing this and thinking "even a budget CRT scope would do this MUCH better... they must be faulty"!
I love the confidence one can have in the results on an analogue scope as what you are seeing is the actual voltage you are measuring and in real time, not an internal computers interpretation of what it thinks happened a millisecond or ten earlier!
I actually have a Tek digital LCD scope (long story.. it's not technically mine but unless the true owner ever turns up/gets in touch... and it's been about 5-6 years now! I won't sell it obviously.. just in case! They were about £2k!)
but I've literally never used it...
Barrymagrec
pfm Member
I used a Tektronix digital scope with a CRT screen a few years ago at a customers premises - I hated the way that the level changed perceptibly after you had probed the signal and that it couldn`t show the difference between a TTL low and a ground short. I didn`t feel I could trust what I was seeing and reverted to a 475 I found lying around at the back of their workshop.
My everyday scope is a 2215, does the job though not as good as a 465 - which I also have but needs attention, which is time.....
My everyday scope is a 2215, does the job though not as good as a 465 - which I also have but needs attention, which is time.....
Arkless Electronics
Trade: Amp design and repairs.
The old Cossor, for vintage oscilloscope "groupies" like me! not my actual unit but mines identical.
The photo doesn't really have scale and the front panel is I would say about 10" X 12-13", but it's about 20" deep!
There are front panel sockets visible between the two channel inputs which are for active probes and provide them with power etc. A large metal protective front cover clips on and contains a "cupboard" which has leads, probes, 50 Ohm in line adaptors and even has spare bulbs and fuses, all in their own foam cut-outs. UK built but developed along with Raytheon in USA and no doubt used by USA armed forces as well as UK at some time.
After my lusting after a vintage valve Tektronix scope a good while back a fellow fishie PM'ed me to say he had just such a thing and it was mine... gratis! But was in, IIRC, Devon... He says that if/when he ever has to travel to the NE he will bring it up
The photo doesn't really have scale and the front panel is I would say about 10" X 12-13", but it's about 20" deep!
There are front panel sockets visible between the two channel inputs which are for active probes and provide them with power etc. A large metal protective front cover clips on and contains a "cupboard" which has leads, probes, 50 Ohm in line adaptors and even has spare bulbs and fuses, all in their own foam cut-outs. UK built but developed along with Raytheon in USA and no doubt used by USA armed forces as well as UK at some time.
After my lusting after a vintage valve Tektronix scope a good while back a fellow fishie PM'ed me to say he had just such a thing and it was mine... gratis! But was in, IIRC, Devon... He says that if/when he ever has to travel to the NE he will bring it up
Barrymagrec
pfm Member
That`s a modern Cossor - I learnt on a 1035 :- https://www.worthpoint.com/worthopedia /vintage-cossor-1035-oscilloscope-16811240
It was full of EF50s Tony.....
My Dad had a proper valve Tektronix, a 546 but I think he passed it on to my nephew. It was quite noisy and in the summer rather warm - basically a 600 watt fan heater.
It was full of EF50s Tony.....
My Dad had a proper valve Tektronix, a 546 but I think he passed it on to my nephew. It was quite noisy and in the summer rather warm - basically a 600 watt fan heater.
Arkless Electronics
Trade: Amp design and repairs.
Yep i'm with you on all that!
My daily scope here is a 465 I "renovated", also on the bench for use as needed is a truly mint virtually unused 453... as good as this one below
They were originally made for IBM computers who gave a spec that they had to be able to fit under a seat in an airplane! Late '60's and hybrid but about 90% solid state... in mine only the EHT rectifiers are valves but v early ones had Nuvistors in the input amps... Was replaced by 465 etc.
I also have a 475 which I went to great lengths to properly sort out, found and replaced all the original problems and got it going but there were all sorts of issues with the timebase switch... eventually had to take the screening covers off and go in... only to find a pillock at some time in its past had tried to do something with switch and knacked some of the incredibly fragile gold plated leaf switches irreparably... and left a small bit of paper saying just "sorry" inside the screened box!
Also have a 466 analogue storage scope... now those were quite a thing! Analogue flood gun transfer storage...
Too big to be practical as it's about a yard deep!!
An SE Labs SM111 (test gear offshoot of EMI) is another one I have and these are great little things, very reliable and can even work off a car battery for field use if required. This was only taken out of daily use when I sorted out the Tek 465.
You know I can't recall the last time I thought any item of mere hi fi gear worthy of posting a pic... 'scopes are so much more interesting... and complicated!
Arkless Electronics
Trade: Amp design and repairs.
Cossor were a pioneer in UK scope tech back in the day... Very nice!
I vaguely recall that back at collage there was a "teaching oscilloscope" made by Cossor... and that it was HUGE! Screen about 12" round, front panel 2' X 2', about a yard deep and on a tall wheeled trolley... rather like the ones that a TV would be wheeled into the classroom on in school back then. I can't find any reference to one on google and I never saw it working...