DIY Valve Guitar Amp Head

[dave.king1]

You could try doing what I did and make a chassis/box from 2mm Aluminium sheeting, I found that 2mm Aluminium sheeting is not very hard to cut with a jigsaw, although you do need some method of folding the sides and tabs up, like a panbrake metal-bending machine, if I could get a decent one I'd be doing more amp builds.

Get some 50x50x6mm angle iron from that unmentionable place and cut it to suitable lengths and stick it in the bench vice, I folded all of the alloy in the car in my avatar by hand using various makeshift mandrels and jigs.

1.6mm alloy sheet cuts OK with a jigsaw if you use a fine blade and run it at high speed.

Word of warning, make sure you use separate blades and flap wheels for steel and aluminum because the particles become highly combustible when mixed and get hot enough. I don't speak from experience with this advice but know a few guys who do

[Simon Barden]

Aluminium + iron oxide = thermite.

[DrNomis_44]

Cheers for that and very good point, yes we don't want other forum members accidentally starting huge fires.


The interesting thing to note is that when you bend a piece of metal, it does have a tendency to heat up a bit at the point where the bend occurs, but it doesn't get hot enough to ignite flammable material, unless the metal is bent multiple times in the same place at a high rate, and then the metal suffers from what's called "Metal fatigue" and then breaks at the point where it is bent repeatedly.

[Marcel]

You could try doing what I did and make a chassis/box from 2mm Aluminium sheeting, I found that 2mm Aluminium sheeting is not very hard to cut with a jigsaw, although you do need some method of folding the sides and tabs up, like a panbrake metal-bending machine, if I could get a decent one I'd be doing more amp builds.

Instead of folding my own I've chickened out and bought a pre-made case from Jaycar. Main reason is it will be fully sealed on the wiring side so the cage that will eventually cover the tubes will not need to be 'pinky proof'. Even though things might seem cramped on the front panel the case does give me enough room for all the controls I want and lots of space inside for all the passive components.

Also going the IEC connector path for mains power in so no grommets or leads hanging an getting tangled out the back whenever it needs to be moved.

https://www.jaycar.com.au/encl-bench...304mm/p/HB5556

[Marcel]

The topic of ESR meters was raised in this tread and thanks to a FB post I've found a modern supplier of what seem to be quite good meters from a UK manufacturer. They also make LCR meters and two versions of transistor testers and of all things UTP testers, all of which are handy bits of gear to have beside your multimeter if you have the need for them...

Manufacturer is... http://www.peakelec.co.uk/

Aussie distributor is ... http://www.altronics.com.au/peak/

[DrNomis_44]

Yep, those Peak meters are great bits of test gear to buy if you're after test gear for amp servicing.

[DrNomis_44]

Update:


My mate and I are going to see if we can grab the two fridges and washing machine from my old flat today, and while I'm there I'm also going to see if I can grab the Valve head and a small LCD TV that my mate gave me, I'm definitely going to be doing work on rebuilding the Valve head next year, starting possibly around February when I start ordering the necessary parts from Evatco.


Update 2:


Okay I've got the DIY Valve head with me at home in my new flat now, some of the green felt covering is crumbling away so I thought that it would be a cool idea to re-cover it in a Tweed Tolex style and add some Fender-style pot knobs, chrome corner protectors, and etc to it.

[DrNomis_44]

One thing I definitely need to do is re-do all the front panel labeling, some of the labeling is a bit askew and looks a bit of an eyesore, so it looks like I need to buy some new letraset sheets as well as all the necessary bits and pieces to get the amp re-built, should definitely turn out to be a fun project, I may even see if I can design a special dummy load that'll allow me to record the amp head straight into my DAW software, via the Audio Interface without disturbing my neighbors....silent recording in effect, there's an adjustable line out on the back panel, and I'm thinking of including a passive speaker emulator circuit of some sort so that the line-out signal can be fed to a P.A. system via a D.I. Box and it will sound like the amp is going through a speaker cab through the Front-Of-House P.A. speakers.

I don't know whether a passive Resistor-Capacitor circuit will work, or a passive Inductor-Capacitor circuit would work better, maybe Marcel might be able to help me out with that.

[Marcel]

Hmmm, dummy load...

Do you remember those old jug elements that use a coil of wire around a porcelain block held in place by two brass rods.... 1500W jug element equates to about 40 ohms of resistance wire. In free air you can push up to about 50W into a unit trimmed back to 8 ohms. Dip that modified thing into a cup of water and the power rating jumps up to a 5minute @ 500W rating. Wilt a bit of forward thinking you could arrange to include 4+8+16 ohm taps.

I use a much larger ceramic 2x8 ohm free air unit rated at 100W continuous. RS and element 14 do sell 100W and 200W bolt down enclosed 4 or 8 or 16 ohm resistors for reasonable prices.

Most (though far less these days) electrical wholesalers have those replacement 1500W or 1200W elements.

As for inductance, you could add a 100uH coil in series to the resistive load, although strictly it is not needed. My ceramic resistance wire jig measures at 0.5uH and most guitar speakers are between 50uH and 100uH and so far I have never encountered an issue. When you calculate it out 100uH is a impedance of about 12 ohms at 20kHz but only 3 ohms a 5kHz and less than an ohm at 1kHz so at guitar frequencies they are significant but usually on the test bench they are not worth worrying about ... They are a huge worry on stereo hifi tube amps pushing large quantities of 20kHz...

[Marcel]

Just read elsewhere that this amp build is to be based on a SLO-100... Is this true?... Do you have a circuit ?... Are you going to include clean/crunch to OD switching via a foot pedal ? ...