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Maddogm
12-05-2017, 11:34 AM
For something to do while waiting for Dingotone to dry I recently bought a bunch of pedal kits and a couple of Lamington Amp Kits

So in this thread I will be building a Lamington Jr 2w valve amplifier

This kit is billed as ideal for beginners as it uses a 12v plugpack rather than 240v mains

You can purchase these as a kit or the instructions on their own. One thing I have noticed with the kits is that the parts supplied don't always match up with the parts list in the manual, mainly the caps not quite matching up (there were a couple I couldn't identify as well) and the pots supplied being 1M linear instead of the 500k Audio listed.

1929319294

The chassis as supplied

19295
one of the holes was missing as well the grommets (the other kit has them) so I bought some grommets from clark rubber and drilled the missing hole and enlarged the other one to fit the grommets. Drilling the thin sheet metal proved to be a challenge and while the end result wasn't pretty, the mess was covered by the grommets.

1929619297

Hardware installed and the first wire started. I need to get an underside shot which I'll do tonight.
I decided to stick with the supplied pots as getting the 500k pots with the same hole mount size was a pita.

wokkaboy
12-05-2017, 11:42 AM
awesome project Maddog, the amp chassis looks like a shallow cake tin haha

good idea to pass time while the DT cures. You have proven this is another option to buying another guitar kit !

Can you please post the link to these amp kits ? I'd love to have a crack at building one

cheers

Maddogm
12-05-2017, 11:46 AM
awesome project Maddog, the amp chassis looks like a shallow cake tin haha
It is. That's why they're called Lamington amps

you can buy them from www.valveheaven.com (http://www.valveheaven.com)

wokkaboy
12-05-2017, 12:41 PM
cheers Maddog they have some cool looking amp kits!

DrNomis_44
12-05-2017, 04:54 PM
Seriously thinking of having a go at building a Lamington Amp this year.

Andy40
12-05-2017, 08:44 PM
Same here doc. Thanks for doing this for us Maddogm

Maddogm
15-05-2017, 09:00 AM
Here's an underside shot having installed the hardware and just getting started on wiring the power circuit:
19347

wokkaboy
15-05-2017, 09:18 AM
looks good Maddog. Are the instructions pretty easy to follow ?

Maddogm
15-05-2017, 09:58 AM
looks good Maddog. Are the instructions pretty easy to follow ?

Yeah, so far. The main issue I've had was when they referred to the missing grommets. They do require reading ahead a bit so you have an idea of what a current step interacts with. It includes testing as part of the process as well as schematics and wiring diagrams which help you visualise what the steps are describing.

DrNomis_44
15-05-2017, 06:16 PM
Jaycar Electronics stock rubber grommets, so if you buy a Lamington Amp kit and you find that the grommets are missing you can buy them from your local Jaycar Electronics store.


Rather than buy a kit, I might try and see if I can source all the parts myself and build my Lamington Amp on a diecast Aluminium box from Jaycar Electronics, needless to say, I'll need to buy a construction manual first though.

Incidentally, I've watched a few Lamington Amp demo videos on youtube and have been quite impressed by how good they sound, kind of Marshall-like, but I could be wrong, nice clean tones.

wazkelly
15-05-2017, 08:08 PM
Would be nice if they came with an attenuator as 2w is OK fully driven, but 15w and higher would be very, very loud indeed.

Yes, I have been looking long and hard at these for months now and always weighing up cost of a completed combo with 8" speaker that is anywhere from $229 for Joyo up to $429 for Bugera or Vox AC4 or BWM for $375 versus building a kit where 2w = $195 or 15w = $295 plus you need a speaker on top of that too. Tend to think 15w with a decent speaker would end up costing more than a ready made and have less features. Just my 2c worth.

Also not so confident playing around with all that current and would have therefore gravitated towards this 2w one. Still pondering and will watch how this turns out with interest.

Simon Barden
15-05-2017, 08:47 PM
Rather than buy a kit, I might try and see if I can source all the parts myself and build my Lamington Amp on a diecast Aluminium box from Jaycar Electronics.

If I was making one, I'd be tempted to do something similar. Far easier to then put it in a proper protective enclosure.

Maddogm
15-05-2017, 11:00 PM
So I'm about 10/15 steps in on the wiring up the power supply section which looks like:
19364

Doc the amps are designed with being able to source parts easily within Australia in mind so you shouldn't have any trouble with that.

Waz, I was also unsure about playing around with the current which is why I got this one as well as a bigger one (buying 2 at once doesn't save on shipping FYI)

DrNomis_44
16-05-2017, 12:41 AM
Just need to work out which Lamington Amp I'm going to try building, all the models on offer look really interesting.

Maddogm
16-05-2017, 05:12 PM
One issue I have come across with the instructions is with the order it gets you to solder things to and around the star ground means you layer stuff above it before you've finished soldering wires to it.
19373
The green and black wire in that picture were soldered in after the diodes and and the resistor.
The star ground being the tab behind the lower diodes
I may have cheated with the black wire

Power supply done:
19374

DrNomis_44
16-05-2017, 07:59 PM
One issue I have come across with the instructions is with the order it gets you to solder things to and around the star ground means you layer stuff above it before you've finished soldering wires to it.
19373
The green and black wire in that picture were soldered in after the diodes and and the resistor.
The star ground being the tab behind the lower diodes
I may have cheated with the black wire

Power supply done:
19374


You could try adding more solder eyelets to the Star-Ground.

Maddogm
16-05-2017, 08:52 PM
You could try adding more solder eyelets to the Star-Ground.
It's more getting the soldering iron etc in there
I think if I was doing it again (like the other lamington amp I have), I'd cut the wires going in there to length and solder that end on before adding the diodes over the top

made some more progress

Oops:
19376

I'm onto the output stage now:
19377

Simon Barden
17-05-2017, 12:07 AM
I was wondering how good a ground connection you get with all the Teflon coating on the tray. Have you done any resistance measurements to the other bolts that go through the tray?

Maddogm
17-05-2017, 07:01 AM
I was wondering how good a ground connection you get with all the Teflon coating on the tray. Have you done any resistance measurements to the other bolts that go through the tray?
There was a lot scratching away with the swiss army knife to remove the coating under the ground

Simon Barden
17-05-2017, 04:13 PM
But you'll also need to do it for the other grounded items as well, such as the transformer fixings. As I said, check the continuity with a multimeter, you may be fine.

dave.king1
17-05-2017, 08:17 PM
Just thinking on my feet about the earthing.

A bit late for this project but lining the underside of the tray/chassis with copper shielding would be the go or maybe better on top so the risk of glue failure and the foil sagging down onto hot terminals is removed , bolts through the copper foil to mount the bits underneath would sort the connectivity issue

Maddogm
17-05-2017, 09:53 PM
The method used in this design is to wire everything to ground AFAICT

DrNomis_44
17-05-2017, 11:08 PM
As long as there are ground wires going from all the ground points to the Star-Grounding system, it's not going to make any difference if the baking tray is covered with PTFE, although the baking tray itself should be at least grounded at the Star-Ground itself so that it can act as a shield.


What I would do is this, drill a hole in the baking tray at some convenient point, a hole for a power transformer mounting-screw would be a good example, then use some sand paper to sand-away the PTFE coating, then work out exactly how many ground wires need to connect to this point (which will form the Star-Ground), then all you need to do is use the same number of solder-tag eyelets to enable each ground wire to connect to the Star-Grounding point, making sure that the mounting screw is long enough.

Using a Star-Grounding system in a Guitar amp is a good way of eliminating earth-loops that can cause hum-noise.


When I get round to building my Lamington Amp I'll demonstrate with some pics how to create a Star-Grounding system, when I do a build diary.

Maddogm
18-05-2017, 08:10 AM
As long as there are ground wires going from all the ground points to the Star-Grounding system, it's not going to make any difference if the baking tray is covered with PTFE, although the baking tray itself should be at least grounded at the Star-Ground itself so that it can act as a shield.


What I would do is this, drill a hole in the baking tray at some convenient point, a hole for a power transformer mounting-screw would be a good example, then use some sand paper to sand-away the PTFE coating, then work out exactly how many ground wires need to connect to this point (which will form the Star-Ground), then all you need to do is use the same number of solder-tag eyelets to enable each ground wire to connect to the Star-Grounding point, making sure that the mounting screw is long enough.

Using a Star-Grounding system in a Guitar amp is a good way of eliminating earth-loops that can cause hum-noise.


When I get round to building my Lamington Amp I'll demonstrate with some pics how to create a Star-Grounding system, when I do a build diary.

That's pretty much exactly the system that's being used except with a single tag The cathodes of the 2 caps are twisted together and soldered up to the tag so form part of the star ground area as well.

DrNomis_44
18-05-2017, 05:27 PM
That's pretty much exactly the system that's being used except with a single tag The cathodes of the 2 caps are twisted together and soldered up to the tag so form part of the star ground area as well.


That should work fine then, as long as there's a good solid ground connection there shouldn't be any problems.

Paul_H
04-06-2017, 07:06 AM
A good solid ground connection is illustrated in Rod Elliott's article on earthing/grounding: http://sound.whsites.net/earthing.htm

If you've never visited Elliott Sound Products (ESP), you'll find a a treasure trove of information for hi-fi and pro audio DIY enthusiasts.

No snake-oil, just sound, practical information.

dave.king1
12-07-2017, 06:43 AM
Any updates on this one

JB RETRO
12-07-2017, 03:04 PM
Yeah, any updates.

Maddogm
12-07-2017, 06:31 PM
I got distracted and haven't been working on it lately. There's a reason my first guitar build is about to hit 2 years without being finished :P

Maddogm
16-07-2017, 03:26 PM
So having decided to do some more work on this and worked out where I was up to.
I soldered one more wire on then discovered that a resistor required for the next step was missing (got sent a couple of extra 100k's instead of the 2 4k7's)

It's the kind of situation that rs-online is awesome for. They will happily send a pack of 10 resistors for $0.65 with free delivery

So I ended up spending more time setting up my work area than actually working on it.

Maddogm
16-07-2017, 03:56 PM
and as I was packing up I found the addendum sheet which said to fix instability on some build they'd replaced 10k's with 100k's. but the resistors being referred to (R15 & R17) are actually the 4k7's.

That would be why I didn't pick it up when going through the parts list

Maddogm
16-07-2017, 04:36 PM
So just to add to the confusion, R15 & R17 are listed on the schematic as 10k. But in the instructions only the values are used, not the R numbers. So R15 is referred to as a 4k7 and R17 is referred to as a 10k. Just to make it more fun R3 & R11 are actually 10k

So hopefully you're all now as confused as I am.

Simon Barden
16-07-2017, 05:50 PM
So 4k7 = 10k = 100k. Easy.

Obviously their values aren't mission critical and it will still make a noise regardless.

I'd add in some 3-way switches and use all three values in those positions, and switch between them to see what sounds best.

DrNomis_44
16-07-2017, 07:32 PM
I'm guessing that the 4k7, 10k, and 100k resistors are probably the negative feedback resistors, in that case, the larger the value the more gain that the power amp will have, but the total harmonic distortion of the power amp will increase too.

Marcel
19-07-2017, 04:52 PM
On the circuit I downloaded the resistors marked as R15 & R17 are grid stopper resistors to the push/pull output stage 6BL8's. There should not be a lot of audible difference between 4k7 or 10k however as they have recommended 10k resistors for stability then that is what you should preferably use.

FYI - In most EL84 push/pull circuits of similar design to the Lammington these grid stopper resistors can be anywhere from 2k7 to 15k however 10k is frequently used. Larger tubes like EL34's often have 4k7 or 5k6 grid stopper resistors. The exact final installed value is highly dependant on the applied DC plate voltage and current, idle cathode voltage and the tube load which is most often determined by the output transformer design and the connected speakers. Their main function is to limit grid current if ever there is excessive positive voltage applied to the output stage grid from the previous phase splitter stage. Instability often manifests itself as self oscillation of one or both of the output tubes, or alternately dramatically shortened life from either or both output tubes.

DrNomis_44
19-07-2017, 06:42 PM
My Marshall MA100C uses four EL34 power valves and each one has a 5k6 grid-stopper resistor on it.

Here's a tip, if you want to stabilize the phase-splitter stage, you can solder a small value cap, say a 100pF/3kV blue disc ceramic cap, across from one anode of the phase-splitter 12AX7 valve to the other anode (pins 1 and 6 of the 9-pin socket), I've seen a Mesa/Boogie Mk I circuit diagram where such a cap was included.

Marcel
19-07-2017, 10:42 PM
Most Marshall designs that I've seen have a 47pF 600V cap between the two anodes of the phase splitter. Did the same in my home made EL34 based 50W amp.

Interestingly, in a AC30 the VOX people use a 4n7 and a 250k pot in series across the other side of the two caps that go to the EL84 o/p stage grids (with 1k5 grid stopper resistors), and call that knob a 'Treble cut'...

DrNomis_44
19-07-2017, 11:02 PM
Most Marshall designs that I've seen have a 47pF 600V cap between the two anodes of the phase splitter. Did the same in my home made EL34 based 50W amp.

Interestingly, in a AC30 the VOX people use a 4n7 and a 250k pot in series across the other side of the two caps that go to the EL84 o/p stage grids (with 1k5 grid stopper resistors), and call that knob a 'Treble cut'...


I remember looking at a circuit diagram of a Vox AC30 Top Boost, and seeing the Top Cut tone circuit and then thinking it was a bit unusual to see something like that in a guitar amp circuit, since I was used to seeing the usual three band EQ tone-stack circuit as found in Fender and Marshall amps.

Marcel
20-07-2017, 09:02 AM
The more I look at tube amp circuits the more they all seem the same to me.

Every one of them use the same or very similar techniques to get a result, That being said, a look at any particular brand will reveal consistencies across most of their models thus contributing to their sound. Pre-amp tubes and power tubes biased a certain way and/or of specific types, tone stacks configured in a specific manner with usual values, bypass caps being typical types and values, plus many other unique features all contribute to that manufacturers typical sound.

So I'm often left with a question in my head that leaves me searching... What is it about a particular model that makes certain genres of guitarist proclaim loud and wide that this or that model is the best for what they play?

All too many times I read on other forums that a guitarist loves model XYZ of a brand but loathes the model ZYX of the same brand yet the circuits are identical. It makes me laugh...and I conclude that it must be the speaker cab, or the age of the caps and tubes, or a minor fault in the amps he is using that has set that guitarists heart ablaze...

I spent much of last night reading the http://sound.whsites.net/index2.html site. Most of the time I was where he talks about tubes and tube amps. He is a HiFi guy that has a lot of good knowledge to offer, but has yet to realise that when it comes to guitar amps the guitarist is not after perfect fidelity or a low THD or IMD. Be they tube or SS it doesn't matter, it is the sum of all those many parts with or without all their faults to sound awesome that the guitarist seeks. A few notes from a mildly distorted Strat into a Phaser and a Echorec and then a small WEM 15W tube amp are instantly recognisable by most as the intro to 'Shine on you crazy diamond', yet the Bass lines to most modern music today is nearly all pure SS... so to a guitarist it is the total combination that counts, not the tubes alone.

Chuck
20-07-2017, 09:27 AM
Hey Maddogm, I'm following this thread closely as about 8 months ago I bought the same kit. Just haven't got around to building it yet!! One thing I want to do is not use the lamington tin, but make an aluminium enclosure for it. There are a couple of bits that look like they've been expoyed to the tin - do you think it would be possible to get them off and then re-epoxy them to a new enclosure? That said, I'm not even sure how you'd get them off! Here's a pic of the offending parts on my kit...

20958

DrNomis_44
20-07-2017, 12:28 PM
I remember building a small valve amp, called a Moonlight Amp, some years ago before I moved to Darwin, the original Valve line-up of the amp was as follows:


V1, EF184 (Preamp).

V2, 6SL7 (Phase Splitter).

V3, 6SN7GT (Power Output).

When I built the Moonlight Amp, I substituted a 12AX7 (same amount of gain but in a 9-pin valve type) because I had no 6SL7 valves in my collection of valves, I also had to make my own output transformer as well, since I had no way of buying on, to make the output transformer I pulled apart an existing one and then re-wound the primary and secondary windings according to some calculations I did with the help of a small book I bought from Jaycar Electronics, and to my surprise it worked first time, after that I made a small chassis for the amp out of some thin aluminium sheeting and then designed/etched a PCB for it, after wiring up the amp I connected it up to a power supply that I scored from the Charles Darwin Uni when I did a basic electronics course, the power supply was capable of supplying all the voltages needed to power the amp, after connecting up the amp to the power supply I switched it on and waited for the valves to warm up and then I switched on the HT supply, the amp worked first time and it was pretty loud for what it was, I could get a pretty cool valve overdrive sound from it.

I'm definitely going to have to see if I can find the circuit for the Moonlight Amp, would be cool to try making it again after all these years, I don't have any EF184 valves but I do have an EF86 that I think I could use as a substitute, both the EF184 and EF86 are small-signal Pentodes in a 9-pin valve format, and I know that I can substitute a 12AX7 for the 6SL7, and I think I still have two spare 6SN7GT valves.


Here's a link to a webpage where you can download a pdf of the Moonlight Amp schematic if you're interested in building one:

http://ax84.rru.com/moonlight.html

Marcel
20-07-2017, 08:51 PM
The EF86 should work well. I've seen only one design with an EF86 in the pre-amp being a 1960's version of the AC15. You might be on to something there.

Haven't had much to do with the 6SN7 so can't comment there other than the ax84 site has plenty of examples for guidance.

Somewhere in my technical library I have an old 'tube substitution' book that was printed in the mid '70's.... would have some golden info if I could find it again, that's provided nobody has "borrowed" it.....

Maddogm
21-07-2017, 08:59 AM
On the circuit I downloaded the resistors marked as R15 & R17 are grid stopper resistors to the push/pull output stage 6BL8's. There should not be a lot of audible difference between 4k7 or 10k however as they have recommended 10k resistors for stability then that is what you should preferably use.

they upped it to 100k on an addendum slip of paper and the supplied parts so that's what I'm going with.

Someone suggested setting up a switch to select between the different values but I think that would just cause problems. Apart from the fact these go between pins on the valve socket, I think they might also be structural to the wiring (provide another solder point / keep wires apart so they don't short)

Maddogm
21-07-2017, 09:13 AM
Hey Maddogm, I'm following this thread closely as about 8 months ago I bought the same kit. Just haven't got around to building it yet!! One thing I want to do is not use the lamington tin, but make an aluminium enclosure for it. There are a couple of bits that look like they've been expoyed to the tin - do you think it would be possible to get them off and then re-epoxy them to a new enclosure? That said, I'm not even sure how you'd get them off! Here's a pic of the offending parts on my kit...

20958

On mine it was just the 2 big caps. I can't remember what he said he used to stick them there but I think it's mentioned in the instructions somewhere (I don't have them with me atm). Possibly on the layout diagram.

Once you work out what it is you might be able to work out if there's a solvent that will get it off. But it might be easier just to get replacement caps as trying to remove them may damage them. No idea on the cost of those though.

Moda
15-09-2017, 05:44 PM
Was reading this thread so joined the forum.
Ive built this and the 15w version. The caps can easily be removed by running a sharp knife underneath. If you need to re-attach them just run a small line of silicone underneath and let dry.
Also watch out for the orientation of the single transistor for the preamp. Its a bit ambiguous in the instructions.
If you solder it in the wrong way the amp will work but you actually get an amazing octave up effect.
Google the transistor pinouts and you will be fine.
I would also like to point out that this still a high voltage amp. Safety first. You will get a jolt if you go poking around without thinking first.
The 2w is actually a great little amp and louder than what you realise.
Have fun!

ScottDot
29-12-2017, 09:36 AM
Hi,
Just finished building the Lamington Junior. which I gave to myself for Christmas.
I'm a total beginner, had to practice soldering on scraps before I attempted to do any real work on actual components.
Build took two days , approx 8 hours but a lot of that was learning how to read resistor bands and working out the correct range and settings on my multimeter.
It was pretty straight forward, though some of the language in the instruction steps took me some time to be confident I was doing the right thing. Also some components (transformers, Capacitors) had been swapped without updating the instructions or parts list (I didnt get an addendum in my kit). Though more experienced builders may have been able to asses the substitutions and get on with it, I needed to email Greg from Valve Heaven a few times to be clear. He answered promptly and seems very enthusiastic that people are building and using his designs. I was also confused about the 10K - 100K substitution that maddogm mentioned.2382323823
23824
Had a few newbie issues like melting insulation off wires by clumsy soldering work (had to de-solder and replace), wrong count on valve pin numbers which took a few backward steps to fix and go forwards again, poor soldering technigue which resulted in a valve socket pin filling up with solder ( had to drill it out, heart in my mouth, but it worked)

The amp is super clean, barely any hum even at full volume Has a really nice creamy overdrive, which start to come in quite early and can be progresively dialed up with the tone knob.

Im using it with a Burny Les Paul from the 80's with original VH1 humbuckers so it has a fat sound to begin with.

Im building a little cabinet with a Celestion Original Series Eight 8" speaker to go with it. Definitely a small room setup.

Attached are two pics - external - I swapped original coloured knobs for volume and tone for chicken heads from Jaycar.
Internal - looks messy, but im happy for my first build.

I will play around with the mods suggested in the instructions to see what difference that may make, just as a learning excercise, im happy with the sound now.
Might have to read some of DrNomis_44 posts to get some more background.
Best wishes to anyone else building this, its easy ( I can say that now.....). and sounds great in a small room/ garage.

DrNomis_44
29-12-2017, 12:55 PM
Looks cool, you should do a demo of the amp.

Marcel
29-12-2017, 01:43 PM
It's a 10/10 from me Scott .... mostly cos you made it work which is often the biggest battle... and bonus points for apparently not zapping the life out of yourself in the process ...

I had a quick look at your pictures and can honestly say that my amp builds when I first started years ago didn't look any better. Getting everything to look neat and professional takes years of practice, mostly in learning what you can and cannot cut or what to do first or last so as to get that 'neat' appearance.

Play and enjoy.... and when you get your cab built we'd all love to have a listen too...

moody
30-01-2018, 07:06 AM
I have also built a lamington 15 watt amp several years ago. It is a great little amp and quite loud.

I sourced my own parts including using cheap variations of several of the valves - e.g. 6n2p (I think) instead of 12ax7

If anyone is in the Blacktown area I still have a fair few of the transformers power transformers which I bought from dick smith as they were getting out of electronics - and the output transformers.

JohnH
30-01-2018, 07:48 AM
Looks great Scott! Im always impressed that people build amps; they kind of terrify me

moody
30-01-2018, 09:31 AM
Looks great Scott! Im always impressed that people build amps; they kind of terrify me

There is a reason for that, they are dangerous. The best person to build one is somebody with a healthy respect for that danger.

dave.king1
30-01-2018, 10:42 AM
If anyone is in the Blacktown area I still have a fair few of the transformers power transformers which I bought from dick smith as they were getting out of electronics - and the output transformers.

G'day Moody,

I'm in the Sutherland area, but keen to talk about acquisition of the transformers if for the mid or larger Lamington, not the junior.

I have priced from Jaycar & Altronics

JohnH
30-01-2018, 10:51 AM
There is a reason for that, they are dangerous. The best person to build one is somebody with a healthy respect for that danger.

One hundred percent

churchie
30-01-2018, 05:24 PM
Looks great Scott! Im always impressed that people build amps; they kind of terrify me

I'm too scared to change my tubes

Marcel
30-01-2018, 07:19 PM
It is always healthy to maintain a solid respect for electrickery and all those lazy electrons that will always take the easiest way to get out of doing real work.

Fear helps in that maintenance of respect. Electrons can act way faster than we can think so you need to be at the top of your game plan if we are to constantly out smart them fast lazy buggers and get them to do the work we want.

By work I mean make our air-conditioner and fridge do its thing, make a light bulb glow so we can see, do whatever it does that makes our smart phones be smart, and gather in numbers to make our wonderful axe builds pump that 4x12 cab.... And that's the problem, when they gather in numbers that is often expressed in Volts, and they gather in huge numbers inside a tube amp, and every single electron is constantly looking for an easy way to get out of doing the work we want....and we can't let them take the easy way out by jumping through us to ground....

The simplest way for us to ensure they all do the work we want is not to touch where they are... Don't touch the wires !!... Only touch the insulating parts, the plastic or the glass or the wood... Never touch the wires or any metal bits attached to the wires be they Copper or anything else!!...

Of course there are metal parts we do need to touch but they should all be earthed. It's the reason for the earth wire to the bridge, and why a power cable has an Earth pin that is connected to the metal chassis of our amps, and why there are Earth pins on power outlets and why Electricians put that Green/Yellow wire on every bit of copper pipe in a house to make them electrically safe. (Note - Green/Yellow stripe wire is an international standard for all and only Earth/ground connections, and the reason those colours are used is because fewest people in the world are colour blind to that combination)

Keep that respect for an (every) electrons laziness and there should be no reason for them to take a possibly lethal short cut through you...

DrNomis_44
30-01-2018, 08:46 PM
Well said Marcel, one thing I always made sure I did when doing any 240V AC wiring in some of the things I built that were powered from 240V AC, was that I always made sure that the fuse was placed in the Active part of the 240V AC mains wiring to the power transformer after the power switch, the reason for that is if the 240V AC primary winding of the power transformer develops an internal short-circuit, then the fuse will blow and instantly (well almost instantly) cut off the power, that's assuming that the fuse is appropriately rated of course, doing this also ensures that the metal chassis will not become live at 240V AC, a very dangerous situation.


I'm definitely going to have to invest in a device called a Megger soon, so I can do insulation testing.

chrissyinbkk
31-01-2018, 02:51 AM
Oh thats just taken me back to the 70's... a megger.... and that was the last time i used one...

Simon Barden
31-01-2018, 05:04 AM
They are still widely used for electrical insulation testing. Megger is a brand name, they now do a lot of test products. https://uk.megger.com/products/insulation-testing
The only problem with them is the relatively high voltages they use (500-1000V) can destroy products which use ELV circuits that aren't meant to be insulation tested.

Marcel
31-01-2018, 05:35 AM
Back in high school we had a few wind up Megger's of different sizes....a very basic instrument that had a crank handle to make it work which often got used by the nasty kids to zap unsuspecting victims...

I have two insulation testers both made by Kyoritsu. Both need to be loaded with 8 AA cells to work (and so have nil crank handle like the old Megger units) and thankfully the batteries last a reasonable time.The newer one is digital and does timing tests on RCD circuit breakers as well as insulation tests at 250V, 500V and 1kV. The older analogue meter one I've had for near 30 years does the same HV tests as well as a highly accurate ohm measurement...

On the HV test settings they both do produce the identified voltage but due to internal high resistance of the meter itself there is very little current. Even when the test probes are shorted together there is only a few micro Amps flowing through the wires, which is enough to give you a small shock and destroy most transistors but is typically not enough to kill a person.

At a price point, for the cost of the digital meter I could have bought two fully upgraded top line PBG kits, and 30 years ago the analogue meter cost half that or what amounted to a weeks wages back then.

dave.king1
31-01-2018, 08:24 AM
Talking of the megger and other wonders of electrickery I remembered this bit of wisdom from first year in college

Ten Commandments of Electrical Safety
(1) Beware of the lightning that lurks in an undischarged capacitor lest it cause thee to be bounced upon thy backside in a most ungainly manner.

(2) Cause thou the switch that supplies large quantities of juice to be opened and thusly tagged, so thy days may be long on this earthly vale of tears.

(3) Prove to thyself that all circuits that radiateth and upon which thou worketh are grounded lest they lift thee to high-frequency potential and cause thee to radiate also.

(4) Take care thou useth the proper method when thou taketh the measure of high-voltage circuits so that thou doth not incinerate both thee and the meter, for verily though thou hast no account number and can be easily replaced, the meter doth have one and as a consequence bringeth much woe upon the supply department.

(5)Tarry thee not amongst those who engage in intentional shocks for they are surely non-believers and are not long for this world.

(6) Take care thou tampereth not with interlocks and safety devices, for this incureth the wrath of thy seniors and bringeth the fury of the safety officer down upon thy head and shoulders.

(7) Work thee not on energized equipment, for if thou doeth, thy mates will surely be buying lunch without thee and thy space at the table will be filled by another.

(8) Verily, verily I say unto thee, never service high-voltage equipment alone, for electric cooking is a slothful process, and thou might sizzle in thy own fat for hours on end before thy Maker sees fit to end thy misery and drag thee into His fold.

(9) Trifle thee not with radioactive tubes and substances lest thou commence to glow in the dark like a lightning bug.

(10) Commit thee to memory the works of the prophets, which are written in the instruction books, which giveth the straight info and which consoleth thee, and thou cannot make mistakes.

Marcel
31-01-2018, 08:34 AM
Talking of the megger and other wonders of electrickery I remembered this bit of wisdom from first year in college

Ten Commandments of Electrical Safety
(1) Beware of the lightning that lurks in an undischarged capacitor lest it cause thee to be bounced upon thy backside in a most ungainly manner.

(2) Cause thou the switch that supplies large quantities of juice to be opened and thusly tagged, so thy days may be long on this earthly vale of tears.

(3) Prove to thyself that all circuits that radiateth and upon which thou worketh are grounded lest they lift thee to high-frequency potential and cause thee to radiate also.

(4) Take care thou useth the proper method when thou taketh the measure of high-voltage circuits so that thou doth not incinerate both thee and the meter, for verily though thou hast no account number and can be easily replaced, the meter doth have one and as a consequence bringeth much woe upon the supply department.

(5)Tarry thee not amongst those who engage in intentional shocks for they are surely non-believers and are not long for this world.

(6) Take care thou tampereth not with interlocks and safety devices, for this incureth the wrath of thy seniors and bringeth the fury of the safety officer down upon thy head and shoulders.

(7) Work thee not on energized equipment, for if thou doeth, thy mates will surely be buying lunch without thee and thy space at the table will be filled by another.

(8) Verily, verily I say unto thee, never service high-voltage equipment alone, for electric cooking is a slothful process, and thou might sizzle in thy own fat for hours on end before thy Maker sees fit to end thy misery and drag thee into His fold.

(9) Trifle thee not with radioactive tubes and substances lest thou commence to glow in the dark like a lightning bug.

(10) Commit thee to memory the works of the prophets, which are written in the instruction books, which giveth the straight info and which consoleth thee, and thou cannot make mistakes.

And yet we so often see those with young and mindless abandon test and fail at each of the above commandments..... the old have adhered without fail...

DrNomis_44
31-01-2018, 09:46 AM
In an ideal world, the resistance of insulation material would measure infinite, but as we all know in the real-world 1+1 rarely ever equals 2, most materials used for insulation measure up to a few giga-ohms, that's 1000,000,000 ohms, or a thousand-million ohms, in addition to that, most insulation materials have what's called the Dielectric-Strength, this is a measure of how much voltage the material can withstand before the voltage gets too great and causes a puncture in the material that allows the voltage to leak through it.

Marcel may be able to elaborate on that.

Marcel
31-01-2018, 10:22 AM
Nah, I think you pretty much covered it Doc... If anyone is curious I'm sure they know how to use Google...

wikid of Oz
31-01-2018, 09:35 PM
Back in high school we had a few wind up Megger's of different sizes....a very basic instrument that had a crank handle to make it work which often got used by the nasty kids to zap unsuspecting victims....

In the first two years of my apprenticeship everyone used to use a megger to charge capacitors and throw at each other to catch. The the great fun nazis from safety and HR put a very quick stop to it. Used to hurt like buggery but was funny as

Andy123
20-09-2018, 04:00 PM
Just wondering if these amps are in any way customisable?
The website mentions it has 2 controls but doesn't say what they are - I'm guessing volume and tone?
How hard would it be to put something like this together with separate treble/middle/bass knobs?

Simon Barden
20-09-2018, 07:18 PM
You'd need a new design to work to, as you'l invariably need another preamp valve to go with the tone stack, so the power supplies need to be a bit beefier.

dave.king1
20-09-2018, 07:42 PM
The 15W Lamington has the extra controls you are looking for at a not massively extra cost, but you will be starting with mains voltages not a power pack.

https://www.valveheaven.com/diy-amp-kits/diy-amp-kit/

Marcel or Doc may have a more suitable circuit for your needs