As it’s now more than 18 months since I started this thread, for anyone who hasn’t seen one of these little machines in operation, there’s a youtube video of the David Gingery winder going about it business here:
http://www.youtube.com/watch?v=FIOocMoRsYQ
For anyone who has built but not yet used one of these little winders or who might be thinking about building one, a few more comments and pics about my experiences might be of interest.
My original intention was to wind a replica Repanco DRR2 coil to build the 1959 BBC Focus Radio out of curiosity, but instead, I wound that coil by hand, having borrowed a DRR2 from forum member Alan Beckett to check the inductances. I built the 'Focus' which confirmed what I'd suspected - basically, it's a crystal set with a two transistor amplifier tagged on, so while it had sufficient volume for headphones, it had extremely poor selectivity. As the BBC layout was very untidy I designed and etched a PCB for it. The coil did it's job fine, but I must say that any lad who bought the bits out of his pocket money back in 1959 - if he succeeded in building it and getting it to work from the untidy instructions - would have been greatly disappointed, and far from being encouraged to get into electronics, would I think have been put off. At that time, circuits for simple one-valve TRFs abounded and could have been built more cheaply, and with much better results. I elaborate on the BBC Focus in another thread some time back here:
http://golbornevintageradio.co.uk/forum/...p?tid=2606&page=2&highlight=BBC+Focus+Radio
Be that as it may, over the last few days I've finally got round to winding a few test coils on my David Gingery version of the original Morris winder machine.
The downfall of this – or indeed any machine that will wind wave-wound coils - is the need for either Litz of cotton/silk covered wire, otherwise the turns will just slip off. Such wire is prohibitively expensive. Using the 45 SWG 'cotton covered' wire, with reasonable results. I wound 500 turns onto a 12.5mm Tufnol former, which turned out to be 105 Ohms, and 4mH. (The resistance of the wire is 4 Ohms per Metre, so the coil consists of approximately 26 Metres). I deliberately made the width of the coil narrow (5mm) to see whether or not the turns would slip off the edge of the coil when several layers have been laid down. I suspect that slightly thicker wire might give better results, but that's a matter of conjecture.
The rate at which the 'waves' arise is dictated by how close the rubber tyred drive disc is either towards the outer perimeter of the coil drive disc, or more into the centre. The rubber tyred disc and the one that it drives form what might be termed a simple 90 degree 'bevel drive'. The closer to the edge of the drive disc, the fewer the waves - the nearer to the centre, the more acute the angle of the waves. The shallower the angle, the greater the risk of turns slipping off the edge of the coil as the layers build up, though the type of covering (silk, cotton etc) and the gauge of the wire will have a bearing on this.
With a shallow angle the turns lie closer together, which increases the inductance for a given number of turns, but on multilayer coils the risk of turns slipping off the edge of the coil is greater.
The instructions in the book, which I referred to in an earlier post explain the relationship of the drive, and why it isn’t possible to use a 1:1 bevel drive, which would be a bit more refined. It states:
'The ratio of the crank shaft to the main spindle is infinitely variable by moving the friction wheel to any position along the shaft so that it contacts the friction plate at varying points. This is an important feature because if the ratio was simply 1:1 each successive turn would fall on top of each other and the desired pattern would not evolve. While a gear drive would be more positive, it would not be possible to achieve the very fine adjustment that can be had with this simple friction drive. It requires only a little experimentation to discover the optimum adjustment for each coil job and for very good results to be had'.
I've wound another coil with the drive disc more into the centre, which increased the rate of the weave and makes the angle of weave back and forth more acute, and I had no difficulty winding a coil of 500 turns, without any slippage of turns. I'm sure I could have increased the number of layers without any problems. However, the downside is that because the turns are more widely spaced one from the next, this has a bearing on the inductance. I'd fitted another cam which affects the width of the coil - this one enabling a 12mm width of coil whereas the one referred to in my first post was just 5mm wide. Though this second coil more than twice the width of the first, and had 500 turns like the first one, the resistance of the wire was almost the same (100 Ohms) but due to the less dense weave pattern, the inductance was only 3mH as compared to the smaller, but more tightly woven first coil, which was 4mH.
I've attached a few pics to help make more sense of the above. The first pic shows the weave of the coil taking shape after 50 turns have been wound on.
In the second pic, two black rings caused by the drive tyre will be seen on mating disc - the outer one shows the positing for the tighter weave (closely spaced turns) - the inner black ring shows the position of the tyre for the looser weave with wider spaced turns. The extent to which the cam disc is offset from the centre dictates the extent of the left and right hand throw if the wire guide, and hence, the width of the coil. The one shown in the last pic is for a 12mm wide coil.
I've also attached a pic of this latest coil.
I'm not winding these test coils to any great purpose - just to familiarise myself with the capabilities of this handy little gizmo and to confirm that it isn't just a novelty but does work as well as the youtube video suggest. I should add perhaps that the inductance of these test coils is far higher than that required for say a replica Repanco DRR2 coil (DRR2: 'Dual Range Reaction 2 Waveband'), in which the highest inductance - that of the long-wave winding, is only 1.5mH, the MW being 170uH and the coupling coil 145 uH.
A bit of a minority interest I know, but I hope this update is of interest to someone.
http://www.youtube.com/watch?v=FIOocMoRsYQ
For anyone who has built but not yet used one of these little winders or who might be thinking about building one, a few more comments and pics about my experiences might be of interest.
My original intention was to wind a replica Repanco DRR2 coil to build the 1959 BBC Focus Radio out of curiosity, but instead, I wound that coil by hand, having borrowed a DRR2 from forum member Alan Beckett to check the inductances. I built the 'Focus' which confirmed what I'd suspected - basically, it's a crystal set with a two transistor amplifier tagged on, so while it had sufficient volume for headphones, it had extremely poor selectivity. As the BBC layout was very untidy I designed and etched a PCB for it. The coil did it's job fine, but I must say that any lad who bought the bits out of his pocket money back in 1959 - if he succeeded in building it and getting it to work from the untidy instructions - would have been greatly disappointed, and far from being encouraged to get into electronics, would I think have been put off. At that time, circuits for simple one-valve TRFs abounded and could have been built more cheaply, and with much better results. I elaborate on the BBC Focus in another thread some time back here:
http://golbornevintageradio.co.uk/forum/...p?tid=2606&page=2&highlight=BBC+Focus+Radio
Be that as it may, over the last few days I've finally got round to winding a few test coils on my David Gingery version of the original Morris winder machine.
The downfall of this – or indeed any machine that will wind wave-wound coils - is the need for either Litz of cotton/silk covered wire, otherwise the turns will just slip off. Such wire is prohibitively expensive. Using the 45 SWG 'cotton covered' wire, with reasonable results. I wound 500 turns onto a 12.5mm Tufnol former, which turned out to be 105 Ohms, and 4mH. (The resistance of the wire is 4 Ohms per Metre, so the coil consists of approximately 26 Metres). I deliberately made the width of the coil narrow (5mm) to see whether or not the turns would slip off the edge of the coil when several layers have been laid down. I suspect that slightly thicker wire might give better results, but that's a matter of conjecture.
The rate at which the 'waves' arise is dictated by how close the rubber tyred drive disc is either towards the outer perimeter of the coil drive disc, or more into the centre. The rubber tyred disc and the one that it drives form what might be termed a simple 90 degree 'bevel drive'. The closer to the edge of the drive disc, the fewer the waves - the nearer to the centre, the more acute the angle of the waves. The shallower the angle, the greater the risk of turns slipping off the edge of the coil as the layers build up, though the type of covering (silk, cotton etc) and the gauge of the wire will have a bearing on this.
With a shallow angle the turns lie closer together, which increases the inductance for a given number of turns, but on multilayer coils the risk of turns slipping off the edge of the coil is greater.
The instructions in the book, which I referred to in an earlier post explain the relationship of the drive, and why it isn’t possible to use a 1:1 bevel drive, which would be a bit more refined. It states:
'The ratio of the crank shaft to the main spindle is infinitely variable by moving the friction wheel to any position along the shaft so that it contacts the friction plate at varying points. This is an important feature because if the ratio was simply 1:1 each successive turn would fall on top of each other and the desired pattern would not evolve. While a gear drive would be more positive, it would not be possible to achieve the very fine adjustment that can be had with this simple friction drive. It requires only a little experimentation to discover the optimum adjustment for each coil job and for very good results to be had'.
I've wound another coil with the drive disc more into the centre, which increased the rate of the weave and makes the angle of weave back and forth more acute, and I had no difficulty winding a coil of 500 turns, without any slippage of turns. I'm sure I could have increased the number of layers without any problems. However, the downside is that because the turns are more widely spaced one from the next, this has a bearing on the inductance. I'd fitted another cam which affects the width of the coil - this one enabling a 12mm width of coil whereas the one referred to in my first post was just 5mm wide. Though this second coil more than twice the width of the first, and had 500 turns like the first one, the resistance of the wire was almost the same (100 Ohms) but due to the less dense weave pattern, the inductance was only 3mH as compared to the smaller, but more tightly woven first coil, which was 4mH.
I've attached a few pics to help make more sense of the above. The first pic shows the weave of the coil taking shape after 50 turns have been wound on.
In the second pic, two black rings caused by the drive tyre will be seen on mating disc - the outer one shows the positing for the tighter weave (closely spaced turns) - the inner black ring shows the position of the tyre for the looser weave with wider spaced turns. The extent to which the cam disc is offset from the centre dictates the extent of the left and right hand throw if the wire guide, and hence, the width of the coil. The one shown in the last pic is for a 12mm wide coil.
I've also attached a pic of this latest coil.
I'm not winding these test coils to any great purpose - just to familiarise myself with the capabilities of this handy little gizmo and to confirm that it isn't just a novelty but does work as well as the youtube video suggest. I should add perhaps that the inductance of these test coils is far higher than that required for say a replica Repanco DRR2 coil (DRR2: 'Dual Range Reaction 2 Waveband'), in which the highest inductance - that of the long-wave winding, is only 1.5mH, the MW being 170uH and the coupling coil 145 uH.
A bit of a minority interest I know, but I hope this update is of interest to someone.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
