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Member postings for AdrianR

Here is a list of all the postings AdrianR has made in our forums. Click on a thread name to jump to the thread.

Thread: Kennedy Hacksaw bearing replacement
23/08/2019 17:33:44

Brut force and ignorance?

Thread: Ultrasonic toothbrushes
23/08/2019 17:32:34

I had an original Philips Sonicare, wonderful tooth brush, when the batteries died I replaced it with another brand but never worked as well. Eventually I just went back to manual.

I think I still have it some where, after all never know when it will be useful, think it might get butchered to make a power cleaning brush for the workshop.

I used to work with US machines, the important thing is US needs a media to travel through, air is not good. So anything that will keep the brush and tooth nice an wet should work. I dont think a dog would appreciate a mouth full of KY jelly. Dog drool is pretty sticky and sloppy, so I would think anything that gets them to slobber would work.

Maybe if you eat chocolate biscuits while brushing your dogs teeth it might create enough dog slobber.

23/08/2019 17:22:41

Question: If I can clean my dog's teeth by feeding it biscuits, why can't I clean my teeth by eating biscuits?

Neil

You can, just eat the same biscuits

Thread: Kennedy Hacksaw bearing replacement
23/08/2019 16:22:40

Graeme,

All the bolts are with nuts underneath.

Did you notice in the manual that you move/ the saw, not the motor to tighten/align the belt. The two holes for the saw should be oval.

Adrian

Thread: Anyone good at fault finding with amplifiers here?
23/08/2019 16:14:38

Neil,

There are quite a few different types. Apart from the silicon rubber type that come pre cut for the package, there are the mastic types and paste types. Each can have a different thermal particles. Ranging from Diamond dust to Zinc Oxide.

Where you dont need electrical insolation e.g. for a CPU you can just use the mastic pads or paste. The commonest OEM type is a grey mastic, that on the first few thermal cycles softens and squidges out.

The best for us mortals is Silver paste, having said that I would happily use white paste too, just not on my gaming rig where I am trying to dump 120W through 1" sq.

The secret is to have the two surfaces flat and smooth. No scratching the old stuff off with a blade. Then put it on very thinly, just a little to thick for engineers blue.

Danger of silver paste is it can conduct, so be very clean when removing old.

If in doubt Artic is a good brand to buy.

If you need electrical isolation e.g. for a TO3 package, you need to use a solid insulation i.e the rubber (or olden days mica) Depending on the type you may also need to use paste too, I have never used paste on the silicon ones.

After a few thermal cycles if you dont have a sprung loaded clip check the bolts are tight.

Adrian

22/08/2019 10:56:39

Joe,

Thanks for that, an interesting read, my excuse is all this came out after I learnt about MOSFETs.

It does infer that the early MOSFETs were stable, but the newer high switching speed ones developed this problem. Neils amp is probably stable as it is quite old, but it could probably benefit from having its heat compounds replaced on the output transistors.

Adrian

22/08/2019 08:06:20

I presume your posted schematic is complete in its output stage, ie, not a 'representation'? I would expect good design would have placed current sharing resistors in each FET output leg when more FETs are added in parallel.

Not sure it is a good idea omitting these resistors..(0.2ohm to 0.33ohm 5watt for your amp)

Joe

Joe,

It is vital to have the resistors for BJTs, as they have a positive temperature coefficient which means the current increases with temperature. MOSFETs do not need the resistors to compensate for temperature effects. MOSFETs have a negative temperature coefficient which means the current decreases as they get warm, this means they self balance.

Adrian

20/08/2019 18:37:36

Back in the day when making differential amps it was common to glue the two transistors together so the temperatures were the same. I doubt your board will allow that, but you could glue a small bit of aluminium or copper between the pairs.

If you still have an offset you could inject a DC offset to T202. As you dont have a separate regulated supply, you will need to decouple it with a capacitor.

Adrian

19/08/2019 17:01:01

The Maplin amp from the 80's, sounds like the ones I built. Fantastic little amps. With the preamps I designed I had so little hum. Even at full volume and no input you had to put your ear against the speaker to hear it.

Now a 4Ohm 100W resistor for a dummy load has turned up, my next job is to fix a 100W Traynor valve amp. Will be fun to play with valves again.

Adrian

Thread: Subscription renewal notice
19/08/2019 16:32:53

Hi,

I have just received a subscription renewal notice which is a bit of a surprise as I was not expecting it till November.

It offers me the chance to upgrade to Print + Digital. It also says downloads are only available on iPad, Android & Kindle Fire.

I am not interested in reading a magazine on my phone when I already have the paper version. What I would be interested in is being able to read back issues, prior to my first subscription. I think it is called the archive.

If I upgrade to Print and Digital, would I be able to view the archive on a Windows PC?

And would it include all the issues back to No1?

Adrian

Thread: Kennedy Hacksaw bearing replacement
19/08/2019 15:57:48

Graeme,

Thanks for the info about the bearings, never know when I might need to change mine.

The un-powered version of the saw was sold with a 4 1/2 " V pulley and it says it should run at 240RPM.

I found this site that has information about the Kennedy.

Adrian

Thread: Borrowing
18/08/2019 11:22:29

I lent a friend an air needle gun and an air accessory set. Quite some time later after badgering I got the accessory set back minus a custom air fitting, which made it useless. Also the spray can had not been cleaned properly. I recently rediscovered the set while moving house, I have now replaced the custom fitting so I could use the air duster to clean the lathe.

As to the needle gun, he denied having it till I pointed out what he had used it on. Then he said he must have sold it on ebay. No apology or offer to replace it.

Needless to say he is not a friend anymore.

 

Oh and my brother borrowed my copy of "its a wonderful life" never saw it again. My wife bought it as a gift, and she is not pleased. Every year the film comes on TV, and the comments start sad

 

Adrian

Edited By AdrianR on 18/08/2019 11:27:58

Thread: Anyone good at fault finding with amplifiers here?
18/08/2019 11:09:52

Hope this is not egg sucking, and it has been 35 years since I last played with electronics.

TR205 is acting as a current mirror. This means that the current flowing down through the TR203 leg is mirrored in the TR204 leg with the ratio of R211/R208.

The voltages you have show on those resistors infer the mirror is working as they should always be similar.

If you know the value of R211 you can calculate the current in that leg. Then gestimate the resistance of the pot by its position and check if the voltage drop across the pot is correct. That will tall you if the pot is bad.

The -21V on TR203 seems to suggest the input differential pair TR201/TR202 and TR203 are working.

5V onTR204 could be about right for a 4V output, but hard to say if it is due to being driven that way or it is due to the clamp diodes D202 - D205 without a parts list.

Intermittent voltage could be the biasing pot vr201, is it an open one or sealed. Open ones are prone to get mucky and noisy. If that went open circuit nasty things would happen as all the output transistors would be biased on.

How hard they would be turned on depends on the clamp diodes.

It is unusual for mosfets to go short circuit but if all else fails, you could try popping out the output pairs, 206/208 or 207/209

Adrian

Thread: Kennedy Hacksaw bearing replacement
16/08/2019 18:36:59

The wear I have is not uniform, the blade carrier and top piece are both convex, and the rails are worn more one end/side then the other. Max wear 0.19mm.

My plan s to mill them flat as soon as I can work out how to hold them at the right angles. Not sure how well it will work on my mill as it is not robust and I will have to use the side of an endmill.

Spring loading the top part sounds like a good idea, I would like to see some pics of that.

Adrian

Thread: Should I begin with mild steel on lathe?
16/08/2019 14:46:09

Christopher,

Re the inserts for aluminium. The main difference is that the surface is polished smooth instead of being just the sintered rough finish. Aluminium has a habit of welding itself to the cutting tool tip, this effectively makes the tool blunt till it is scraped off. The rough surface of **M* inserts makes it happen a lot faster than the smooth surface of the **G* inserts. The **G* inserts can be used on ferrous materials and may produce a better finish as they can be sharper.

I would still keep using the **M* inserts for general ferrous turning as they are cheaper, keep the **G* for finish cuts and Aluminium.

I did not see it mentioned in the thread, but EN specifications are the "old fashioned" names. You may also see the steel quoted as.

Free cutting EN1A = 230M07

Leaded free cutting EN1APb = 230M07Pb

Mild Steel EN3b = 070M20

There are lots of others, this is a good intro then just to scare you the European BS EN

Adrian

Thread: Flash player
16/08/2019 14:05:19

The latest versions of chrome come with an inbuilt version of flash that Google maintain to minimise the risk.

If you are using Chrome you will probably need to follow this guide to enable it.

Adrian

Thread: strange power socket
16/08/2019 09:16:07

I can see why that socket did not catch on, it is three sided like USB. Try to plug it in, it does not fit. Turn it over and it does not fit. Turn it over again and it fits. wink

Thread: Kennedy Hacksaw bearing replacement
16/08/2019 08:11:12

Graeme,

What a coincidence I have just bought a Kennedy too, luckily the bearings are good, but the hex slides are worn. Being cast in there is no chance to replace them.

What state are your slide in?

Adrian

Thread: Grinding your own lathe cutters
15/08/2019 08:10:43

Have you heard of tangential tool holders? Lots of designs around if you want to make one and I am in the middle of trying to design my own. Eccentric Engineering make one, see the adverts on this site, and there are some youTube videos about tangential tools.

The big advantage of this type of tool holder is you only need to grind one face.

Adrian

Thread: Small Volume PCB printers?
14/08/2019 14:11:45

All depending how much of the board is missing and what the circuit is, but you can just use thin wires soldered on to replace the missing parts. Solderable enamelled wire is an easy way to go, as the enamel comes off with the soldering iron and flux. No stripping needed. Tack it to the board with super glue or hot melt.

Also there are pcb repair pens that use a silver loaded glue, all you have to do is draw the new track.

Only time this could be a problem is if the board is carrying high frequencies where the board itself becomes part of the circuit due to its inductance and capacitance.

Of course it does not work so well for multi layer boards, I assume yours is either single or double sided, not a multi-layer one.

Edited By AdrianR on 14/08/2019 14:13:33

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