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New challenge for 2022 - Hiwatt DR103 Clone amplifier.

Andy Betts

First of all...... Hasn't it changed a lot around here??

I've been away for a long time, and thought I'd dip back in and get doing electronic stuff again. Up until now if you've followed my previous posts I've been building guitar effects pedals. Well, that's progressed onto building actual guitars of which I've now built 5 in the last year or so hence why I've been missing from the element 14 community. Now i'm back with a new project which i think may stretch me.... And I know I'm going need to call on all my element 14 friends for support with this new project. You know who you are John Wiltrout's Blog 

For years I've dreamed of owning the holy grail of guitar amplifiers... The legendary Hiwatt DR103 100 Watt Amplifier. Well, this year I've decided to research as much as possible and build myself a clone. A genuine Hiwatt DR103 sells for around £2,600 ($3,519)I've calculated that I can build one for around £1000. I intend to source all the main parts from https://modulusamplification.com/ in the UK, and https://www.tubeampdoctor.com/en/ in Germany.  I might buy the transformers from the US, as I want exact clones of the original Partridge transformers as used in the originals. I know there's a company in the US that does make these.

I shall share as much information about the amplifier as possible, and will use this forum post as a conduit for trouble shooting. I'm well aware that I may need a scope for this build so I'll seek out a cheap one to get me out of trouble with this. Hopefully it'll go smoothly with just having to check voltages etc. There is a fantastic website devoted to the Hiwatt DR103 and other Hiwatt amplifiers, this is the resource I'm using for schematics etc. https://hiwatt.org/

Here are some gut shots of an original early 70s DR103.  All the wiring is point to point using turret boards. No PCB's here.

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On paper it shouldn't be too hard to build. But as with all these things there's always issues along the way. First things for me to buy are the chassis, the tube sockets, turret boards, etc The transformers will be bolted on first, then everything else will be propagated around them. 

Let me know what your thoughts are, and if you can foresee any issues that i need to be aware of.

  • in reply to shabaz

    Fuses may be good too : ) It's clear you are trying to replicate the design faithfully, but at that cost, I'd be adding fuses. You can get wire-ended coated ones (ie. they don't look like a glass cylinder) that would not look out of place to a causal observer, they look like resistors.

  • in reply to shabaz

    Also, the 'scope would be the minimum, you might also want to get a disposable external USB sound card, and a disposable laptop in case it gets damaged, and have accessible attachment points from the preamp portion, (and measure the voltage with a multimeter with AC measurement capability first) so you can test it (and optionally tweak things if you wish - you might not if you want it identically replicated), and similarly, a way of being able to isolate each output stage, e.g. a place where you can remove a wire link to insert your own load and test each tube output at a time.

  • in reply to shabaz

    I'll be utilising 2 x 3a slo-blow fuses. One is internal and the other is accessible via a fuse holder on the rear of the amplifier. As i'm in the UK the power fuse is rated at 3a, where if i was using the amp in the US I'd have to change it to 6a

  • in reply to shabaz

    I'll be buying a Variac to help with testing, along with the scope and a DMM. Most people that build these only require those 3 things. But all your suggestions are noted.

  • I'm on the scrounge.... I'm looking for 2 Mullard Mustard axial capacitors. 22nf 400v to be exact. Like these in the picture........ If anyone can help it'd be much appreciated. I've checked Ebay and the going rate for these at that voltage is stupid money, circa £15, $17 EACH!!!!! I really don't want to pay that if I can help it, so maybe someone here might have 2 squirrelled away from an old project?

     image

  • in reply to shabaz

    Ahh... Matched tubes/valves.... There's another story. I may well hit a brick wall with this project as the valve stocks are suddenly drying up due the war in the Ukraine, and I haven't purchased them yet. A major percentage of valves are manufactured in Russia, and Electro-Harmonix who purchase them from Russia to sell on are obviously no longer in a position to buy them anymore as Russia has imposed a ban on the export of around 200 goods, valves being one of them. Because of that a lot of guitarists have been panic buying tubes and stockpiling them away. my main supplier www.tubeampdoctor.com based in Germany is completely out of the valves required for this project, with no indication of a restock.

    You can read about the ban here guitar.com/.../

  • Just to give you as much information as possible, I've uploaded a few layout images. One of these is from a company called MOJO Tone, they sell a kit based on an early 70's Hiwatt so I've included it here. I've very tempted to follow the MOJO Tone schematic and layout. They're clear, and accurate to an early 70's Hiwatt 100. The first image is a layout diagram of an original Hiwatt..... There's virtually no difference between the 2 layouts.

    image   image

    image

  • in reply to Andy Betts

    Awesome! Thanks for the link. Now to go scrape up some money from the school to drop an order.