"Indicated Hot"

[Dragondreams]

Hi all

Following an invite to post some pics in my "Introduction" thread, I figured this might be the best place...

I got hooked on building a valve amp for my guitar playing hobby. I'm a "bedroom" guitarist and have my own mini-studio here. I have an Orange OR120 and a pair of Crate 4x12 cabs. WAY too much horsepower unless I want to annoy neighbours (and not just in my street!).

I discovered Merlin Blencowe's site (and consequently bought his books) then set about building myself a low wattage guitar amp that had masses of gain. I like huge overdriven sounds...

The more I looked into building my own, the more I realised that there's not really anything new! When I finished "Indicated Hot", I realised that it's more or less the same as an AX84 Hi Octane. My dad, a retired electronics engineer, pointed out that there are only so many ways a valve amp can be built after all.

The name is an anagram of "The Addiction". I run my own guitar-based forum and the name was suggested by one of the members there. Apparently, I posted about nothing else but building this thing for weeks!

Anyhoo. As promised. A couple or three pics of the build.

The basic building blocks for the pre-amp are shown below:






The prototype was built into a chassis I picked up cheap from an internet auction site...


I got the mains transformer from Barry at Ampmaker and went for one of his multiple voltage versions so I could fit a power scaling switch.


The first prototype worked fairly well, but I had a few issues with noise and just far too much gain in each pre-amp stage.


Once I'd ironed out the wrinkles (more attenuation between stages), I bought a chassis from Maplin and a punch from Rapid Online. wanted a chassis that would give me plenty of room to experiment at a later stage.


I'm missing a few pics of the latter stages of building, as well as the diagram for the output section. It runs either an EL84 or a 6N1P, selected with a switch on the front panel. Combined with the voltage selector it gives me a wide range of sounds at different volume settrings.

The finished product sounds quite versatile, and ticks all the right boxes for my own personal taste.

There's a very poor piece of video here of me testing the finished build. I was too excited to play properly, and the phone I used to make the video wasn't the world's best.
http://www.dragondreams.org.uk/indic...icated-hot.mp4

[indianajo]

Nice.
Are those phenolic headers under the chassis in the last picture? You solder discrete parts on them? Where did you get them? what does the vendor call them? I have a source here in the US, "terminal strips" from tubesandmore.com, but sometimes I recommend them to people in Europe and intercontinental inter-country shipping is expensive and fuelish.

[VictoriaGuy]

Originally Posted by indianajo

Nice.
Are those phenolic headers under the chassis in the last picture? You solder discrete parts on them? Where did you get them? what does the vendor call them? I have a source here in the US, "terminal strips" from tubesandmore.com, but sometimes I recommend them to people in Europe and intercontinental inter-country shipping is expensive and fuelish.

Also called 'Tag Board' by some suppliers, I think.
Arena Electronics Ltd Amplifier Parts

John

[Dragondreams]

Originally Posted by indianajo

Are those phenolic headers under the chassis in the last picture?

I get them from RS Components and they call them "miniature SRBP base for group panel". I've always called it tag strip | Connectors | Terminal Blocks or DIN Rail Terminals | Tags and Barrier Strips | Tag and Barrier Strips They're pretty cheap at £1.20 for a pack of five.

I like doing point to point construction using tag strip, but my next one will probably use turret boards. I sometimes end up struggling because I don't plan the build order and end up with some components getting in the way of my soldering...

Here's a couple of pics of the finished innards of the amp.


I changed from LED biasing back to resistor biasing during one of the rebuilds though.

The finished version of the amp also lost two of the gain stages, so it now only has three and a cathode follower.

It's big brother has five gain stages, but I didn't bother with the triode/pentode output options or the voltage scaling.

[Nigel Goodwin]

Originally Posted by Dragondreams

I get them from RS Components and they call them "miniature SRBP base for group panel". I've always called it tag strip

Those are actually tag 'board', tag 'strip' is just a single row where every fifth one (usually) is longer and has a right angle fixing hole at the bottom.

You can use two rows of tag 'strip' to do like you have (bearing in mind that every fifth one might connect to chassis) - but the reason for using tag 'boards' (like you have used) is so you can assemble the board, then fit it in the chassis. With tag strips you have to fit the tag strips, and then fit the components one at a time.

Valve amplifier design seemed to evolve from:

1) Tag strip

2) Tag board

3) PCB

Nothing wrong with any of them, but it got cheaper to make as it evolved, and that was why it was done.

[Dragondreams]

Originally Posted by Nigel Goodwin

Those are actually tag 'board', tag 'strip' is just a single row where every fifth one (usually) is longer and has a right angle fixing hole at the bottom

Thanks Nigel, that makes a lot of sense.

I have some of the tag strip that you mention, but I found the tag board a lot easier to use.

[Nigel Goodwin]

Originally Posted by Dragondreams

Thanks Nigel, that makes a lot of sense.

I have some of the tag strip that you mention, but I found the tag board a lot easier to use.

Which is why manufacturers moved to it - both have (or at least 'had' ) their uses.

Some guitar manufacturers have actually moved back to tag board, simply for historical reasons - and so they can charge more. There's no actual advantage over a PCB, apart from if you're making a one-off yourself.

[Dragondreams]

Originally Posted by Nigel Goodwin

Some guitar manufacturers have actually moved back to tag board, simply for historical reasons - and so they can charge more.

I tend to agree with that one. "Point-to-point" and "hand-wired" are certainly buzz words that I'm starting to see more often in advertising bumf in the guitar mags.

However, there are some schools of thought, mainly from "boutique" manufacturers (boutique = VERY expensive collection of the self same parts) that reckon a PCB acts as a capacitor and affects the "tone mojo" of a valve amp.

Personally, I don't see that an audience would notice the "tone mojo" of a heavily overdriven 10 watt valve amp being relayed to them via a massive multi-kilowatt PA system at sound pressure levels that effectively shuts down their hearing.

It might be a different matter in a recording studio...

I used tag board in these projects (Indicated Hot has a bigger brother) because it made my life simpler. I learned to design and make my own PCBs many years ago, back in the days before PCs and easy to use graphics software. Using tag board meant I probably had the amp finished and working in less time than it would have taken to lay out and etch a suitable PCB.

[VictoriaGuy]

Originally Posted by Nigel Goodwin

There's no actual advantage over a PCB, apart from if you're making a one-off yourself.

Unless you want to be able to replace components repeatedly....most PCBs get 'lifting pad' problems quite easily.
And, tube sockets on PCBs are not something I like at all....but they are getting more common.
John

[Nigel Goodwin]

Originally Posted by Dragondreams

However, there are some schools of thought, mainly from "boutique" manufacturers (boutique = VERY expensive collection of the self same parts) that reckon a PCB acts as a capacitor and affects the "tone mojo" of a valve amp.

No problem on a valve amp, where quality is fairly low anyway.