Capacitor Tester and Reformer Unit - Stefan Niewiadomski

[Terry]

Stevie, you are quite right - what I described is a one-off method but I did also say: I used this method successfully for a wide variety of boards and modified it slightly to allow me to make multiples of the same board - some quite complex - without having to redraw the layout.

Quite simply, because I used an A4 graph paper pad I dew the PCB on the top sheet. Then, without detaching it from the pad, placed a thin sheet of paxolin or similar under a number of sheets equivalent to the number of copies I wanted. I then went round with a sharp needle - a pair of compasses from a drawing set worked well - and pierced the pad positions through all of the sheets at the same time. I then used the same method as I described before with the bradawl to transfer the pad pattern to the boards. If there was any possibility of missing a pad, I added a pencil tick to each hole so that I could easily check for any that I'd missed.

The accuracy of the pad placement and the component holes were the most important part of the process. After that, drawing in the track pattern on each board was relatively easy.

Of course, if I'd had access to a UV exposure unit and suitable track layout transfers - a company used to provide Letraset style pads and tracks in handy packs under the Alfac name - I would have used them!

Of course, no-one ever dreamt of the possibility of today's design programs and cheap small quantity prices in those days!

[Stevie342000]

Although slightly off topic for this thread, thanks all for the help and understanding.  I think the reason I never went any where near solid state was I had seen first hand the results of others who were far more competent than me in printing PCBs.

Yes I remember Letraset, the etching solution and the pcb marker felt tips, it usually ended up less than professional.  I saw the issues with this plus it bugged me if I could not replicate exactly a professional finish.

With all the options we have now who would have thought how easy it would be for the professional and the layperson to get the same results at such an affordable price.

Plus I think for me solid state circuits  looked more complicated as it often had more components than what was used in valve technology which schematically was easy to follow, I sort of got lost in the complexity of solid state and perhaps the other reason is that valves were simple circuits which gave excellent results so why complicate it by going solid state.

The chances for errors with extra components are increased and any faults are harder to find, back to that simple technology again.  But I have to say that my understanding has increased a lot over the last 40 years and since the advent of the Internet with all its resources that has significantly increases in more recent years.

[Terry]

The symbols weren't Letraset although the rub down technology is the same. Alfac is the brand I remember and I think Seno was another. You can get an idea here.

However, you don't need PCBs to use transistors, nor do you need the metal working skills demanded by 'chassis bashing' for valve radios. Stripboard, like Veroboard, with copper strips punched at 0.1" intervals, was ideal for transistor circuitry. The only special tool you needed was a spot face cutter to remove the strip around a hole to make a break in the track - or you could use a suitable size twist drill bit or even drill right through the board, but the tool was easier and neater.



One of the advantages of Veroboard for the beginner was, if you used transistors with the common e-b-c pin out, you could virtually transfer the printed design directly to the board, which could take up a fair bit of room but you would soon learn how to adapt the layout to save space like this.

Of course, the 0.1" graph paper was ideal for planning layouts with its 1:1 scaling.

You could soon find that, with a bit of careful thought, and most, if not all, of the components mounted vertically, that you could achieve very dense population densities.

[Terry]

DON'T TRY THIS AT HOME, FOLKS!

I first dabbled with PCB production while I was still at school. I hadn't come up with the nail varnish resist idea at this time and I hadn't a clue where to obtain etching materials but I had another idea. A boy in my class was seriously into chemistry and had struck up a rapport with the pharmacist down the road who would let him have things us other oiks wouldn't be let near - so I asked him if he could get me some concentrated nitric acid!

When I explained why I wanted it, he agreed so, one Friday night after school, I waited outside while he got the acid which he presented to me in a small brown bottle sealed with a cork! With his instructions to keep the bottle upright at all costs ringing in my ears, I set off for home.

Ten minutes walk to the underground and down the stairs. Two stops then change. Up the stairs, down the stairs and wait for the train home. I managed to jam myself into the corner seat for support for the 35 minute journey, then it was off down the High Street and home - about a 12 minute walk. Once indoors I walked right through the house and out of the back door before setting my bottle down on the window sill.

I then decided to remove the cork from the bottle and found to my horror that it wasn't in the bottle but rather resting on top of the bottle with a thin sliver of burnt cork protruding into the neck! I carefully placed the bottle somewhere where it couldn't be stumbled upon by anyone, man or beast, and went inside for my tea.

The next day was Saturday and time for the great experiment. I'd already prepared the board using the graph paper technique to mark the pad positions then drawn the track layout on the polished copper using a black fibre tipped pen only recently introduced by Platignum at a cost of 2/6.

I'd melted some candle wax with which I'd then succeeded in coating the board in a thin layer. Being translucent, I could still see the track drawing through it. Now out came the school compass and, using its point, I'd laboriously scratched a groove all round each section of track, making certain I could see the copper in the bottom of the groove.

I placed the board on the concrete coal bunker, which was conveniently slightly slanted and retrieved the acid. I has a glass applicator from an old bottle of drops which was ideal for getting the acid out of the bottle, being careful - of course - not to squeeze the bulb too hard before sucking!

I dripped the acid into all of the grooves, take advantage of the gradient to distribute it evenly and continued until all reaction stopped. I then washed the board thoroughly and melted off the wax. A quick once over with metal polish to remove the ink pattern and there it was: my very first PCB! All that was left was to drill it and mount the components but now, almost 60 years later, I haven't a clue what it was I was building!

[ppppenguin]

When in my teens I tried etching PCBs in nitric acid. Dilute rather than concentrated. I think I acquired it at school from a friendly lab tech. To my delight it was much quicker and cleaner than ferric chloride. Until the day I used some that was too strong. The resultant brown fumes were not pleasant.

[Diabolical Artificer]

Z = out is very roughly your anode resistor, or not so roughly 0.14 - 0.4 x Ra. But strictly speaking Zout is Ra in parallel with the dynamic resistance. Z in is roughly the grid resistor. But this is very approximate because impedance is dependant on frequency, so a gain stage or OPT will have a different Z at 20hz than at 20khz due to valve interelectrode capacitance's and an OPT's inductance. Even then it's hard to find some power valve's capacitance's from the datasheet to base your calculation's on, then there's stray C and shunting C; it can make your head hurt.

The only math's I use in building amp's are ohm's law, f = 1/(6.28xRxC). This can be juggled to find cap and R value's for RC filters and loads of other stuff. About the only other thing I use is multiplying RMS by 1.414 to get peak value or DC once rectified. I manage to wing it without anything else finding it easier to measure stuff once built.

For quick PCB's I use a dremmel to cut out the traces once having drawn the layout on a bit of paper. I use a sharp cutter to cut the traces and drill the holes, then deburr using a round ball bit. Not as neat as etching but quick.

150w OTL amp's! They'll be tricky, what will you use some sort of follower?

Andy.

[pwdrive]

I don't quite follow the Z out bit...

Lawrence.

[Stevie342000]

The following below comes with a do not try this at home warning

Thanks all for the hints and tips, the Audio Note Preamplifier kit that I had was a variation on the veroboard style of mounting the components, in that there was holes where the components went and the leads were linked on the underside of the board, sort of a halfway house between pcb come veroboard  and hard wiring.

Yes I do know that impedance is a variable not a constant.  But also checking my understanding here.  Andy in your example on using Ohms Law (which I do follow) what does the 6.28 represent and where does it come from?

OTL uses PL509 or Pl519 remember my preference for not solid state.  Its a variation or based on a Futterman and as far as I can tell no chance of putting DC volts on the speaker.

Ah yes and finally those good old chemistry days, a friend of mine (a group of girls no less) made a hole in the school playing field, when they threw the bottle of nitroglycerine which they had made in the school lab, the tech support knew what they were doing.  But the best one was their chemistry teacher who was due to go to a wedding that weekend and they had stuffed the tap with potassium permanganate.  I do not remember why she was rewarded with this but, the class that did the deed were not the one she was teaching at the time.

My family friends went to a proper school and I went to a state school so of course were much more advanced than me but I had enough of an understanding.  We did all sorts with sulphur, sugar and nitrate, adding weedkiller (his father suggested that one), its a wonder we did not burn the house down.  I seem to recall that the father suggested using aspirin as well.  Of course in those days you could go to the chemists and get these items, no chance of that now, oh those were the days.

When I was much younger I got a chemistry set for a present and proceeded to use it in the Kitchen, I mixed up my chemicals and   heated it up, it boiled, then it  spurted up the wall and I wiped it off along with the paint. What I had made was paint stripper, oh yes I was popular I think it had just be repainted at the time.

My goodness if you did any of this these days or attempted it you would have special branch round before you knew where you were and would be under a very strong light whilst being interrogated.  There's not a lot of fun in life if that is the case growing up any more for kids.

Another trick was once we had made our mixture we would get two nuts and a bolt pack it with the stuff and then heat it, other tricks were to take bare mains wire (his house had no on off switches on the sockets either) and drop the bare lead into water and watch it bubble.  We often had the leave the room after some experiments as you could not see across it and even with the windows open it took time to clear, of course there were other tricks their garden was big enough for us to drive cars around, which we did and we were encouraged to do so by the parents, again these days we would all be under special provisions or in care.  It's what I call a childhood we were not wrapped up in cotton wool we lived full and productive lives and were encouraged to experiment.  

But I digress....its a habit....now I recall we tried to that too if only we had know you could get the concentrated nitric acid from the chemist (we tried making it but could not get it strong or pure enough), probably that time had past even though we are talking 40 years ago approx.

Oops did it again.....

[pwdrive]

6.28 = 2*Pi.

Lawrence.

[ppppenguin]

2 pi is sometimes called Tau (the Greek letter)

http://tauday.com/tau-manifesto