Portable cabinet – some bits missing

The jig is ready to use.  I will coat it all in varnish as soon as I can as the MDF will absorb moisture and warp which would not be useful at all.  But I need to get the Portable HiFi System started so want to use the jig straight away.

Having just gone through the MDF cut parts for the portable’s cabinet, I find there are errors;  I only ordered 1 part of an internal vertical when there should have been two ordered and I created a .dxf (CAD/CAM files) with dimension of 227mm instead of 277mm and those two parts were the side walls.  Rather, were meant to be.

So, a little setback.  I will need to get these three MDF parts from somewhere.  I cannot use the original cutter company as they have gone and I don’t want to use the current cutting company as it is only 3 parts.  I may have to cut them myself somehow, maybe I need to buy a circular saw of some kind.

Hopefully the next post I make, will be with a full compliment of fingers.

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Box Construction Jig now Faced

Box construction jig: the faces are now glued in place. All three faces need to be perpendicular to the other two; not so easy to do in practise. As I adjusted one set another face would be pushed out of true so it was a little tricky to accomplish but I am happy with the results.
I used the side panel from a dead Apple computer to check for accuracy (it has holes all over it because I was using it for a dual, variable power supply).

There is a gap around the bottom face to stop the two pieces being glued from sticking to the jig faces.  The gap is 30mm so I can join MDF sheet up to 25mm without gluing the jig and the cabinet pieces into one solid lump of MDF bits.

Box Construction Jig with the three faces glued into place.

Box Construction Jig with the three faces glued into place.

Box Construction Jig being checked for perpendicularity / accuracy using a panel from a dead Apple desktop computer.

Box Construction Jig being checked for perpendicularity / accuracy using a panel from a dead Apple desktop computer.

Posted in Box Construction Jig, cabinet, Construction, Ghetto Blaster / Portable Music Player, Loudspeakers, Power Amplifier | Tagged , , , , | Leave a comment

Box Construction Jig is now being built

The emergency decorating is now finished, we are through Christmas and it is time to start building the box construction jig so I can start the build of the first Portable HiFi thanks for your patience Frank!

I made a couple of mistakes with the dimensioning of the jig so those needed correcting – it wasn’t at all straight forward and meant me staring at it for some time, trying to work out the best way of solving the problems.  Those problems are now solved.

I now have to find a way of putting it together so it is absolutely accurate regarding perpendicularity etc – I cannot get it wrong when it’s glued together as my boxes will be out of kilter.  Getting all three sheets (not shown in the photos as they need to go on next) glued accurately into position is not as easy as I expected.  When is anything as easy as you think?  So that is the next problem to solve but when it has been I will have a good jig to start all my MDF box building (amplifier, speaker cabinets etc).

I’ll post another photo when the three flat sheets are glued on.

Main box construction jig supports.

Main box construction jig supports.

All the box construction jig supports.

All the box construction jig supports.

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Portable Stereo HiFi development

The MDF has now been cut by Stalite Signs of Exeter, to produce the Box Construction Jig.  There are one or two problems, basically mistakes I have made and need correcting before I proceed.

But that aside, our outside wall has some cracks in the lime plaster (the house is over 220 years old) and the damp has destroyed some of the plaster inside our house.  So before I can carry on with the Portable Stereo construction, I need to do some exterior and interior decorating as it will only get worse.  And now I have discovered it, it will get worse fast and much quicker than I expect, Sod’s Law and the fact it’s winter and all that . . .

I hate decorating.

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Why do you need Lasting Power of Attorney?

There comes a time for all of us when the people who are closest and dearest to us, reach an age where they are not physically and/or mentally as capable as they used to be.  This usually happens late in life but can also happen earlier.  Especially with older people, I cannot help but feel certain institutions are circling above waiting to swoop down and grab any morsel they can get their beaks onto, so protecting our loved ones best interests can potentially, turn into a fight.

My wife’s parents.  A very good friend of ours, who has recently been through the same landscape, advised obtaining a Lasting Power of Attorney straight away, both for finance and also health.  I searched the Internet for reasons why I might want to do that but all returns were from institutions that made money from instigating a PoA and though it all sounded good, they clearly are biased as there is a large financial return for them.

So my wife asked my friend for some idea of why PoAs are a good idea.  His answer was so good I thought it worth sharing here so that others may benefit.  You will find my wife’s email below, together with his response.

There is a point I would like to make.  I had difficulty convincing my wife to talk to her parents about it as she did not want to come across as money or power grabbing.  It turned out that her mother was only too ready, willing and happy to proceed.  But her mother was reticent to talk to her husband due to concerns he would not like the idea.  It turned out that my wife’s father was also only too ready, willing and happy to proceed.  A lot of dangerous time had been unnecessarily wasted through trying not to hurt anybody’s feelings but nobody’s feelings were hurt at all.

  • Do not waste time worry about feelings as this is far too important.

A second point here.  Having convinced her mother and father to go ahead, her mother downloaded all the documents from the government web site, both finance and health ones and then asked her neighbour to be a witness to the signatures.  Their neighbour has known them for nearly two decades now and was in a good position to do this.  Unfortunately the neighbour then convinced the mother to not bother with the health one as it would save £82 for each of them and wasn’t really necessary as “your doctor has your best interests at heart and the health one is a waste of money”.

  • Do not let someone with no knowledge and only a single experience talk you out of this.

I’ve just entered my 60’s and though I consider myself far away from needing any kind of Power of Attorney, I will donate this to my wife as soon as possible now I know more about it:  you may not need anyone else to drive your car but if you put someone on the insurance, they are legally able to drive you to a hospital when you break a leg and they don’t get access to your car when your leg is good.

Government Web Site for Power of Attorney:


A lasting power of attorney (LPA) is a legal document that lets you (the ‘donor’) appoint one or more people (known as ‘attorneys’) to help you make decisions or to make decisions on your behalf.

This gives you more control over what happens to you if you have an accident or an illness and can’t make your own decisions (you ‘lack mental capacity’).”

Here is something that may or may not be relevant, a BBC 28 minute video on;

Communication and Dementia
Michael Rosen explores how to communicate with people with dementia. Alison Wray offers advice, such as to respond to the feeling behind the words rather than the words themselves.


That’s the end of my rant, here’s the good stuff.

Hi *,
Sorry to bother you but could you please give me some advice?

My mum has decided not to go for the health part of the power of attorney paperwork. Could you outline for me the reasons that you’ve come across why this might be a bad decision on her part?

Both my mum and dad are more than happy for the financial power-of-attorney paperwork but I don’t know why they wouldn’t want to have the health POA.


Hi 🍁,

Not a problem, I’m always happy to spout forth my opinion on things!
Caveat – everything I say is my personal opinion & may or may not be factually correct, in fact it could all be complete drunken bunkum!  🙂
An outline requires brevity – sorry, not my forte so your will to live may wane under the weight of my reply!
Firstly – maybe your mum has the standard generational thinking of our elders…don’t cause a fuss, doctor / lawyer / vicar / person of “importance” & “standing” knows best & is always right, etc.
Nonsense of course because one has every right to question & “cause a fuss” as it’s one’s health after all & believe me, doctors are not always right & the NHS often makes arbitrary decisions based on finances or outmoded medical thinking, puts juniors in charge, etc, etc…………….hospital “nutritionists” & the Liverpool Pathway spring to mind as prime examples of how not to do it that I have personal experience of.
Secondly – your mum may not want to give such angst ridden responsibilities to her loved ones – that’s you by the way 🙂 – & would rather let the system do it’s thing & absolve you of any responsibility for what may happen to her in a worst case scenario.
Admirably intended but misguided! – nothing is worse than seeing decisions & actions being made for your loved one’s health that you know are wrong (either factually or simply against what you know to be their wishes) & being helpless to do anything about it.
If you are not PoA for health then medical practitioners will usually listen to your thoughts as a relative but DO NOT NEED TO ACT UPON THEM, THEY CAN OVERRIDE / IGNORE YOUR INPUT in a contentious circumstance.
If you are PoA for health then you are legally deemed to be that person in the event that they can no longer make decisions themself….the doctors have to speak to you as if you were that person!
Thirdly – fear!  Fear of having control of her life taken away from her & your mum is possibly also fearful of acknowledging the unpleasant possibility of being in such a position in the first place.
She can rest assured that a PoA is only applicable if & when her health / mental capacity deteriorated.
Also, any specific wishes that your mum has can be written in to the PoA so that you have to abide by them – all decisions you make have to be in your mum’s best interests & not in yours. The ability to put specifics into the PoA (such as blood transfusion, Do Not Resuscitate, organ donation) protect your mum against any eventuality that she may not wish for.
It is also a fact that just because you may be acting for her under the PoA in a certain situation, it is not a legal “given” that you can act in for your mum in each & every scenario.
Ie: she may not lose total control over her life. There is legal precedent that lack of capacity, once acknowledged, can not be assumed in every occasion – this might seem at odds with what I’ve said earlier but imagine not being given the basic human respect of not being asked first what you’d like to eat, wear, do next, etc – these are basic things but important to one’s dignity.
(Also, there are far more complex situations which would not apply to your mum but for which this legal precedent is very important).
Fourthly – your mum may have had poor legal advice. A prime example here – my late mum initially decided to only do the finance PoA because her solicitor told her that there was enough protection in the law anyway for her health!
After all, a medical professional has to act in their patient’s best interests. But why would there be a PoA for health at all then? What if one disagrees with their opinion of best interests / does not wish to go along with their proposed treatment?
I knew from previous experience that this is utter rubbish & when I rang my own solicitor for their input they simply could not believe that my mum’s solicitor had advised her that way!
My mum, my brother & my sister all agreed with her solicitor (see my first point about some people doffing their caps & blindly believing that those in authority somehow always know best) & I frankly had to give up arguing about it with them all.
Move on a year when my mum had been very ill & had also changed solicitor – to one who as it happened advised differently, she changed her mind & took out a PoA for health!
Move on another year or two when dementia took mum’s ability to think for herself on so many things & we were all very glad that she had PoA’s in  place.
Basically, a PoA (be it health or finance) is a way of making sure that what one wishes to happen is what happens – it protects the rights of the donor (in this case your mum) in the event that they can not speak for themself.
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Dual Amplifier CV1460 Incandescent Lamp to LED Conversion

How to convert an amplifier or receiver from incandescent lamps to LED lamps

I use a Dual CV 1460 amplifier for my office/workshop and not just because it sounds good; I like the looks too.

Mostly the reason I like the way it looks is because of the big, analogue VU meters it has on the front.  But they were lit with incandescent lamp bulbs and I had already replaced them once when they all went again.  So this time I have replaced them with LEDs which should last a lifetime.  In this post I will document how I replaced them including the calculations.

The original incandescent lamps were rated at 12V/110mA as can be seen on the Service Manual circuit diagram.  The current is irrelevant to us as that will now be dictated by the resistance of the new LEDs.

Figure 1. Circuit diagram from Service Manual.

Figure 1. Circuit diagram from Service Manual.

I bought the LEDs to replace incandescent lamps in a Harman Kardon HK 730 receiver and had a few left over.  I could see that I had written on the packet I kept them in “12V/1W”.

I do not like the lamps on my equipment to be bright as I find it intrusive so I put one of the LEDs across the output of a power supply and gradually turned the voltage up.  The LED lamp came on at around 7.0V (note there are several LEDs within each lamp hence the high value of 7V) and was at a brightness I liked at 8.0V so with 3 in series I would need 24V dc to power them.

The original lamps were powered by 35V ac and they were also in series giving a voltage of 35 / 3 = 11.66V across each – so a little under-rated which is a good way to increase their lifespan.

Figure 2. My drawing of the original lamp circuit.

Figure 2. My drawing of the original lamp circuit.

LEDs conduct (and therefore give off light) only when a positive voltage is applied to its anode.  This means an ac voltage would cause the LED’s light to flicker at around 50Hz (mains frequency) and that can be seen by the human eye especially when one’s eyes are moving.  So I didn’t want that and to get rid of it I decided to use a bridge rectifier giving full-wave rectification.  With full-wave rectification the ac waveform output from the bridge is approximately 1.414 times the input less a volt or two for the voltage drop across the two conducting diodes (the exact voltage depends on the diode and how much current is being drawn).  So off-load (no current being drawn) the output voltage from the bridge is 35Vac x 1.414 = 49.49Vdc (off load – remember the voltage will drop a little across the diodes when conducting, usually around 0.6V for silicon and around 0.3V for germanium but who uses them anymore).  I used an electrolytic capacitor to smooth any ripples on the voltage output, it doesn’t need to be exact, anything between 47µF and 470µF is fine so long as the rated voltage is well above what it has to cope with – I would have preferred to use a 100V cap but 63V is Ok.

Figure 3. My drawing of the new lamp circuit.

Figure 3. My drawing of the new lamp circuit.

In the same way that the original lamps had a third of the input voltage across them, the LEDs will also drop a third of the voltage giving them each about 16.5 volts – too much.  Some of the voltage has to be dropped across a resistor (RL) to get rid of the excess.


As said above, the LED lamps had “12V/1W” written on their packet.

Watt’s power law says: W = V x I

Therefore: I = W / V = 1 / 12 = 0.08333A = 83.333mA or to put another way 83.333×10-3A

NB:  Since all three LEDs and the resistor RL are all in series, the same quantity of current flows through each of them.

So we know that the new LED lamps should have a current through them of 83.33mA at 12V.  But since I would be using them at 8V, the current/wattage used by them would change.  Why is it important to know the current or wattage?  The voltage applied to the LEDs is too high so must be reduced.  This is done by using a potential divider network which is a fancy name for what you see in Figure 3 above; the output from the bridge rectifier (at 49.49V) is across the resistor RL and three LEDs all in series (the capacitor is only used to smooth the voltage peaks, it can be ignored in these calculations).  The voltage of 49.49 volts is divided across each LED and the resistor.  For the sake of ease, lets say the voltage is 100V.  If the LEDs were 200Ω each and RL 400Ω then there would be 2V dropped across each LED and 4V dropped across RL.  The voltages dropped would be the same if the resistances were 2000Ω and 4000Ω (respectively) but the current would drop to 1/10th.  This is why the current/wattage/volts rating of the LEDs is important; it tells us what their resistance is and from that we can work out the resistance of RL.

But we aren’t running the LEDs at 12V and being a semiconductor, their resistance will not be the same at 8V (it is notable that the resistance change is non-linear).  However, when I put one on the power supply, I had a multimeter measuring the current flow and saw that at 8V it was 3.5mA – or thereabouts but it was a good starting point to calculate the LEDs’ resistance.

RLED = V / I = 8 / 0.0035 = 2285.7Ω

RLEDTOTAL = 2285.7 x 3 = 6857.1 = approx. 6857Ω

We want 8V across each LED which totals 24V across all three.  That leaves 25.49V (49.49 – 24) across RL.  So RL has to drop 25.5V.  We can now use Ohms Law to work out the resistance of RL:

RL = V / I = 25.5 / 0.0035 = 7282.85Ω which is approx. 7K3Ω.

But as already stated, the resistance of semiconductors changes depending on the voltage applied and it changes in a non-linear fashion and there is also the tolerance of the resistor to take into account so . . .  having constructed the circuit and turning on the amplifier, the LEDs looked a little dull.  When I measured the voltage across the LEDs they were 7.82V, 7.8V and 7.77V – all too far away from 8V so I wanted to get the voltage up closer to my ideal of 8V.  This meant I needed to reduce the resistance of RL so it has less voltage dropped across it, leaving more to drop across the LEDs.

What if I used the next common value down at 6K8Ω? Using the formula to work out the potential divider network:


( 6857 / 6857 + 6800 ) x 49.49 = 24.848V across all three LEDs.

24.848 / 3 = 8.283V across each LED (on average) which is perfect.  They look great, just right to me (brightness-wise).


Close up of power conversion circuit.

Close up of power conversion circuit.

Distance view of the lamp PCB.

Distance view of the lamp PCB.

Close up of power conversion circuit.

Close up of power conversion circuit.

The LEDs stood off from the substrate by about 5mm.

The LEDs stood off from the substrate by about 5mm.

I soldered wire to the LED's two connectors.

I soldered wire to the LED’s two connectors.

Bird's eye view of power converter and LED.

Bird’s eye view of power converter and LED.

CV 1460 amplifier using LEDs, in situ.

CV 1460 amplifier using LEDs, in situ.

Posted in Circuit Tests, Power Amplifier, Power Supplies, renovation, Testing, Vintage HiFi Renovation | Tagged , , , | Leave a comment

Woodwork drawing in for production

The drawing for the Box Construction Jig is with Stalite Signs of Exeter.  I have accepted their quote and they have sent the drawing to their production department.  When cut I will have woodwork for the jig but also one pair of Main 1A speakers together with their accompanying Subwoofer Stands and an Amplifier 1A.  I already have woodwork for the Portable HiFi.

Stalite cut all sorts of materials for sign makers but are also open to cutting for any other type of project.  They have been helpful and communicative – there is nothing worse than a company ignoring your emails.  With luck, this should be a good, ongoing relationship.

Box Construction Jig plans for Stalite Ltd.

Posted in Amp Cabinet, cabinet, Ghetto Blaster / Portable Music Player, Loudspeakers, Power Amplifier | Tagged , , , | Leave a comment