Dave's Lamington 15watt build

My first blog! I discovered a way to custom-make your own valve guitar amps, using inexpensive,readily-available components; it's all thanks to a guy called Grant Wills, who's designed and circulated 2 designs,a 15 watt and a 50 watt version,built in a lamington baking tray (hence the name).If, like me, you love the sound of valve amp for guitars, and have basic soldering skills, I strongly recommend having a go; I've built both of them, and they're just what I needed (I'll bore you with my playing history later on).I'll attach some photos of the 15-watt version first; if this works, I'll post construction details (everyone's approach will be a bit different, but it's good to have a starting point that can be modified to suit your own approach).Here goes...

A bit later on:
                     Well, the blog made it, so I'll continue; to find out more, go to http://www.ozvalveamps.org/ava100/ava101lamington.htm to find schematics, construction tips, etc.As with any valve amp,location of parts,orientation of transformers,twisting of heater wires,etc is important, so I recommend reading up on the subject to minimise annoying noises. For my build, I chose to use tag strips for a number of reasons; if nothing else, it's easy to check your wiring- just make sure not to use more than one earth point. I happen to have nylon nuts and bolts,and standoffs in large supply...I had to estimate where to put them,my next build will be neater. After a scary episode (trying to re-solder the power supply before the caps were fully discharged) I fitted a standby switch with bleed resistor connected when you're not playing; turn off the power, and it's safe to touch in 10 minutes.The power transformer is from my junk box (60v,80VA), and the heater supply is a 12v1A DC plugpack-I had to rotate the transformer inside the case to minimise hum, hence the gaff tape to hide the silicone I used to re-seal it.The finished amp sounds great;at first I used a pair of 6EM5 output valves acquired for almost nothing, but they cooked themselves, so I bought a matched pair of EL84s, and all was well. The beauty of a 15 watt amp in a small room for jamming is that you have much finer control over your volume, and it's working hard- I've used master volume amps for years,but they tend to swamp the finer details of your playing. With the Lamington,you can stop hitting your guitar so hard to play arpeggios,and clearly hear the individual notes, which are more prominent.I could be wrong about this, but my feeling is that if your amp (both pre- and power-) is at full volume for moderate playing,it doesn't get (much) louder as you smash the strings, just more distorted, so it gives you dynamic range without frigging around with any controls (in a funny sort of way, it turns your electric guitar into an acoustic one, playing-wise).Have fun!

Finally; pictures of my 50w variable-power Lamington (aka the "Woody",due to the wooden front panel)
I've been testing this amp for a little while now; seem to have got all the annoying noises out (I had a faulty brand-new pot and a couple of dodgy solder joints in the tone circuit, but I sorted it out eventually. Been running it almost once a week since February.I happened to have an old hi-fi amp case that the Lamington tray fitted into; removed the front panel,cut a bit of plywood, rub-down letters from K-Mart, it looks like this:

The drive pot is there for future expansion, but I wanted this amp to distort of its own free will; basically crank it right up,adjusting the volume by increasing or decreasing the HT voltage.I've had some success using a variac (as long as you keep the heater voltage the same;cold valves sound crappy!),but that was quite unwieldy.I have a multi-tapped power transformer that I used for the HT-by selecting the taps,I can feed between 45-110v AC in 10volt steps to the tripler circuit, which supplies roughly 190 up to 420v DC to the amp.I placed a fan near the transformer, because triplers can make them overheat-so far,it's behaved itself ,I ran it at full volume for 2 hours on my bench, and it got warm but not hot.To power the valve heaters (and the fan), I used a discarded Toshiba laptop power supply-15v,2A switchmode (via dropping resistors)-this enables me to use a variac on the whole amp, if there isn't time to fiddle about selecting the taps, which live inside the amp for safety- here's how the inside looks:

The tag strips at the top of the picture are for the different voltage taps,selected by the red,blue and black connectors. I need to point out that this is a personal foible of mine- there's no need to make your build this complex.Also, a switchmode power supply can induce nasty buzzes into the system- once I earthed the centre-tap of the power amp valve heaters, it settled down.I fed the bias ajustment pot shaft to the top of the chassis, for ease of adjustment- being in a case, it won't get bumped.I put a 3-position toggle switch for the standby, which allows On, Standby, and Capacitor bleed modes- the last one being for safety; turn off the power on the rear switch,and watch until the indicator light goes out, then it's safe to poke around inside it.This is how the chassis looks:

I trimmed the pot shafts to length once I got it sitting in the case properly...
Another thought I've had since I built it is that this variable-power approach might not suit a lead guitarist (I can play lead, but I prefer not to).The reason is that the amp is working as hard as it can for your rhythm,so it doesn't have any headroom- solos don't seem to jump out as much as they should ; but for bashing chords,or choking back the volume in a small room,it works really well. There's no perfect way to get a "loud"sound when you're playing quietly, but this is the best solution I've found yet- master volume amps are all very well, but they crush your dynamics, and picked notes and arpeggios get lost in the wash (the way I play, anyway)...A huge thank-you to Grant Wills, he's an inspiration to us all; if you can solder, or know someone who can, you can now custom-make your own valve amp