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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.

image        image

image  image

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.

  • What are your expectations for the amplifier?

    Tube amplifiers sound to some audiophiles as the closest to the original sound. Clones, compatible and replacement components all have the potential to impact the performance of the unit. The schematic dated 1994 might make some of the original components more available, some others like the transformers, well is that compatible the same as the manufactures?

    I would make a list of all components to get an idea of the amount close to the original parts you will have before putting out the cash.

    What do you estimate your cost will be to build from scratch versus purchasing a unit?

  • in reply to colporteur

    To buy a new amplifier is around 2.5k... to make one is around 1k

  • Just a heads up regarding this tube amplifier. This is NOT an Audiophile amplifier. It's a guitar amplifier that used with an external cabinet to amplify an electric guitar. I think got the wrong end of the stick. 

    I totally agree regarding making a list of the parts, and I've already started doing that in an excel spreadsheet with costs applied to each item. That way i can track exactly how much this is all going to cost. I'm at around £800 currently, but I have only listed the main components so far. Chassis, Valves (or tubes for my US friends), the cabinet, the 2 transformers, the wiring, and a few other odds and sods. I have still to list the resistors and capacitors etc. but they shouldn't cost too much.

  • It might be easier to mount anything that requires flipping the chassis before the transformers. Wiring can be done after the transformers are anchoring the chassis.

  • in reply to Andy Betts

    The price point is ideal. Best of luck.

  • in reply to dougw

    Totally understand why you'd say that. However once the transformers are in place and the valve (tube) sockets are all in place, the chassis can be turned upside down then 90% of the wiring and turret board stuff is done like that so no problem there. Also the wiring for the valves (tubes) are done like that. Literally, I'd install the transformers, the capacitors, and the tube sockets then that's all that done. Flip over to complete. Last thing will be be install the tubes, but that comes last after testing with just the rectifier tube installed

  • in reply to Andy Betts

    That is what I had in mind. Most of the wiring doesn't require flipping the chassis. It actually makes assembly much easier to have it all on one side and anchored to transformers on the other side. And the chassis ends up hiding all the (ugly) wiring.

  • I've started taking delivery of some of the cheaper, smaller items.... All the turret boards have arrived, along with all the 1w and 5w resistors, tube sockets, pots, capacitors etc. I need to buy the chassis so I can start laying out the items within it. 

    image   image

  • in reply to Andy Betts

    Excitement is building. WHere did you purchase the turret boards? I would like to use them for a solder class for students.

  • I don't know anything about tubes/valves, but if I were doing it, I'd strongly recommend buying a lot more 22k and 100R resistors, and measuring them, to create a matched set for your project, if you've gone to the effort of buying matched tubes/valves for the output stage. That's if the ones you've bought might have 5% tolerance or so, instead of (say) 1%.

    Maybe it won't make much difference, but there's no harm in this strategy since the price of more resistors is tiny compared to the overall cost of the project, so perhaps it's better safe than sorry - and additionally it might improve the audio slightly too (no idea).