DIY Valve Guitar Amp Head

[DrNomis_44]

Before I moved to Darwin in 2000, I bought a kit from Jaycar Electronics which was for building a device called an ESR meter, you'll probably know what ESR stands for Marcel, but for the benefit of other members, ESR is short for Equivalent Series Resistance, now the ESR of a capacitor is an important specification, in Electrolytic Caps you want the ESR to be as low as possible, usually it's about less than an Ohm in fairly large value Electrolytic Caps, the ESR of a Cap is the Effective Series Resistance that the cap presents to AC, and is a very good indication of the health of the Cap because when the Cap goes bad and dries out, the ESR skyrockets in value, or goes high, lower value caps, eg say a .022uF/600V PIO type, will have a higher ESR than say a 47uF/450 V DC Electrolytic, Low ESR is an important spec for Caps because you tend to find a lot of low ESR Caps in modern Switchmode Power Supplies.

I might see if I can dig up my ESR meter and do some restoration work on it so that I can use it again, I think it just needs a couple of new test leads made for it, and maybe a new 9V battery clip, if I can't find it I might see if I can buy a new ESR meter kit from Jaycar cause there's supposed to be an updated one.

I think at least one of my DIY guitars uses a .1uF PIO cap as the tone cap, they are pretty good sounding, to my ears the common garden-variety 100V Greencaps seem to have a tone that has a harsh high-end to it, or maybe I'm just imagining it....lol.


When you choose a Cap for use in an electronic circuit, you have a few criteria that the Cap needs to meet, for me those criteria are as follows:


1, Working Voltage- (Very Important) The Cap needs to have a Dielectric (plate insulator) that is able to withstand the expected voltages in the circuit when the circuit is energized, or powered up, otherwise the Dielectric will puncture and develop a short-circuit.

2, Tolerance- (Not so important in some cases) The tolerance of a Cap is how much it actually measures in value +/- the marked value, most modern Electrolytic caps can actually measure anywhere from +/- 10-20% of the marked value on the Cap, in some cases, like in tuned radio circuits, or audio filters you want the tolerance to be fairly tight, note that most of the time it's not that critical.

3, Physical size- This is relatively self-explanatory, you wouldn't want to try and use a huge oil-filled can-cap in a circuit designed to fit in a case that's about the size of a matchbox.

4, Age- Again self-explanatory, you wouldn't want to use a Cap that's so old it's literally crumbling away to dust.

[Marcel]

I think at least one of my DIY guitars uses a .1uF PIO cap as the tone cap, they are pretty good sounding, to my ears the common garden-variety 100V Greencaps seem to have a tone that has a harsh high-end to it, or maybe I'm just imagining it....lol.

Many years ago I ran a workshop in the Valley in Brisbane servicing all sorts of amps and gear. I very quickly learnt that happiness of the customer was paramount, and a substantial part of that happiness was catering to their beliefs about gear. Which gear sounds best, which gear is crap, is it worth it to do this or that modification, and so on. Quite often I'd end up replacing a perfectly serviceable part with another because the other had some reputation that the muso wanted in his rig. I'd charge the muso accordingly , they'd walk away happy, and recommend me to their friends... so it was all good. Nine times out of ten I couldn't tell any difference, but they could, so I lived with it, it was their money that they were spending. In a sense I felt they were buying happiness, which made them play better, but I couldn't tell.... These days I have the time to spend looking at and repeating for myself those changes I did back then, and despite my own issues (Tinitinitus or whatever) and in my own way I'm starting to see and hear what those muso's back then and now were on about.... go figure...

My ESR meter works fine, as does my Z meter... I'll post some pix soon to illustrate what you said there Doc... I have a few new and old dud caps floating around here somewhere...

[DrNomis_44]

Many years ago I ran a workshop in the Valley in Brisbane servicing all sorts of amps and gear. I very quickly learnt that happiness of the customer was paramount, and a substantial part of that happiness was catering to their beliefs about gear. Which gear sounds best, which gear is crap, is it worth it to do this or that modification, and so on. Quite often I'd end up replacing a perfectly serviceable part with another because the other had some reputation that the muso wanted in his rig. I'd charge the muso accordingly , they'd walk away happy, and recommend me to their friends... so it was all good. Nine times out of ten I couldn't tell any difference, but they could, so I lived with it, it was their money that they were spending. In a sense I felt they were buying happiness, which made them play better, but I couldn't tell.... These days I have the time to spend looking at and repeating for myself those changes I did back then, and despite my own issues (Tinitinitus or whatever) and in my own way I'm starting to see and hear what those muso's back then and now were on about.... go figure...

My ESR meter works fine, as does my Z meter... I'll post some pix soon to illustrate what you said there Doc... I have a few new and old dud caps floating around here somewhere...

Cheers mate, that would actually be good so that other forum members can see what it's all about, it'll be interesting in any case.