Maddog's Lamington Jr Amplifier build diary

[DrNomis_44]

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]

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]

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]

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...

Attachment 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]

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]

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.

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]

Looks cool, you should do a demo of the amp.

[Marcel]

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]

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]

Looks great Scott! Im always impressed that people build amps; they kind of terrify me