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TubeNexus » Blog Archive » Your first DIY Guitar Tube Amp Project

Your first DIY Guitar Tube Amp Project

by Mark ~ April 23rd, 2008. Filed under: Amplifiers, tube amp electronics.

If you have decided to take the plunge and build your own guitar tube amp, please let me share my early mistakes projects with you to help get you going in the right direction.  But first, be sure you really want to build your own:

  • You should be fairly handy around electronics already, and aware of the dangers inherent in high voltage tube electronics and the precautions to take when working on tube amps
  • You shouldn’t have the expectation that you will save money… unless your time is worth nothing at all you can probably do better purchasing a completed amplifier, even from the kit vendors, but certainly on the open market as used

All said, though, there is a lot of satisfaction in completing and playing an amplifier you built yourself and having the license to further modify/tweak/voice your creation to perfection.

My First Project

My first project started as an AM radio. It wasn’t based on the All-American Five (AA5) circuit, instead it had a proper power transformer (Hammond 272X60), was tube rectified, had a single 6V6 for the power tube and used metal can octal tubes for the other active devices.  I had done a number of radio restorations in the past but this custom radio chassis didn’t have a cabinet or a schematic and I had only kept it for parts.

Shortly after I picked up guitar as a mid-life hobby it occured to me that this chassis and most of the components was quite suitable for an octal-based champ-like single-ended amplifier and I wanted to hear the difference in tone between real tubes and the tube modeling in my Roland Cube Amp… so another hobby was born!

I picked up a copy of TUT3, found a number of octal-based amplifier schematics to reference on the web and dug into the project in an adhoc fashion.  I stripped the chassis to bare metal, cleaned up all the sockets, threw out all the IF transformers, resistors and old capacitors and then re-assembled the components I needed with strategically placed terminal strips to implement true point-to-point wiring. I followed the distributed power filtering guidelines in TUT and also implemented the ground lift and star grounding method. I built a single-stage preamp initially (6SQ7) and then experimented with ‘high-gain’ and added another 6SQ7 but also tried a pentode tube (6SJ7).  I used the output transformer in an ultra-linear fashion.  Making changes to the point-to-point wiring soon grew tiresome and the thought of adding a proper tone stack to the circuit was daunting.

Major findings in this first effort:

  • I fought with the old transformers (insulation turning to dust when you flexed the leads), used tube-sockets, noisy potentiometers and poor physical layout (working with the old radio chassis didn’t provide optimum placement of the major components for a tube guitar amplifier)
  • The ground and filtering scheme worked really well… very little hum even open-loop with this design
  • True point-to-point wiring isn’t the best choice for experimenting
  • Couldn’t find a non-microphonic old-stock pentode tube
  • The tone sucked… with hindsight I believe it was due to the underwhelming, un-branded, tiny output transformer, but I’ll probably never go back to check
  • Bottom-line, I learned a lot but it didn’t answer my fundamental questions about tube-tone because I didn’t end up with an iconic amplifier as a reference at the end of the project

 

My First Kit Project

I decided that I wanted to build an iconic amplifier and I wanted a full kit of parts including cabinet for my next project. My first choice was a ‘59 Bassman kit but I balked at the price and decided that I should test the kit waters a bit by building a Champ initially. I researched on the web extensively and decided to try a kit from a very popular kit/speaker supplier.  I ordered an oversized output transformer so I would have winding taps for ultralinear mode and made the necessary modifications to isolate jacks, etc. for star grounding as well as adding additional power filtering and virtual center tap ground on the heater AC. Later I added a Baxandall tone stack when I found a convenient place on the back panel for it to mount.

Major findings on my second try:

  • Saving a few pennies here and there on components isn’t satisfying when you end up investing a lot of time building the project and aspects of the end result look cheap (e.g. a plastic replacement for a ‘proper’ metal construction jeweled pilot light) or worse… sacrifice tone (e.g. cheap electrolytic capacitors)
  • I’ve grown a bit leary of un-branded chinese transformers that may not have even been hi-pot tested let alone certified by a safety agency; and who knows what laminations, etc. are used in the audio transformer?
  • Tiny chassis and cabinets aren’t the best choice for adding additional functionality to the stock circuit and very frustrating to work with
  • 8″ speakers and small cabinets suck… this amplifier sounds great when you plug it into a proper speaker & cabinet combination
  • I think this project started to live up to the old adage that you shouldn’t try to “stuff 10 pounds of s**t into a 5-pound bag.”
  • I kinda veered from my original goal of a completely iconic amplifier due to the limited useability of a stock Champ in the end but did get satisfying tube-tone experience from this project
  • Limiting my investment worked out… I didn’t go back to the original kit supplier for a Bassman kit

 

Considerations for Your First Project

With the above experiences in mind it is time to summarize some considerations for the first project:

  • Simple project but not under-featured… something that will be satisfying and playable
  • Physically large for easy access, simplified assembly and room to modify
  • Well documented, well supported… not necessarily with user’s manuals and step-by-step construction guides, but rather by a community with active forums, or extensive web documentation, etc.
  • A complete kit of parts, no difficult sourcing of components
  • Good quality parts with the potential to upgrade them if desired… but moderation rules… you may want good value over extravagant components to minimize your downside if your project doesn’t come out well or you lose interest.
  • Standard sized chassis for easy sourcing of cabinets, or cabinets available from the kit supplier, or a desire, determination and ability to build (and finish) your own cabinetry

 

My Recommendation for Your First DIY Guitar Amp Project

Subsequently, down the road a bit from my first two experiences, I decided to build a Trainwreck-inspired amplifier and had read a posting by GeetarPicker (Glen Kuykendall) about how well a Ceriatone “Expression” had tested against a real Trainwreck Express amplifier.  To keep a long story from getting any longer: I bought an Expression in kit-form from Nik at Ceriatone and had a wonderful experience with the product and the customer support, so I heartily recommend Ceriatone for your first amp kit.  I tell you all about building my Trainwreck-inspired amplifier in post(s) to follow, starting with: Ceriatone Expression Build, Part 1.

Now, to be clear, I’m not specifically recommending a Trainwreck-style amplifier as your first project… these beasts are an acquired taste and definitely not everyone’s cup of tea.  But Ceriatone has a wide range of products and offers flexibility in kitting and assembly on all of them.  The component quality is very good, not extragavant, and the only consideration I would give is to substituting a popular brand of transformers for the asian manufactured ones that Nik ships… but for the money involved, you might do that as an upgrade later. Projects like the Marshall-inspired 18Watt, the Trainwreck-inspired and the Dumble-inspired amplifiers are well represented by strong communities of hobbyists that can help you succeed with your first effort.  Choose carefully with your own tastes and capabilities in mind… but keep my considerations above in mind as well!

Good-luck with your first project!

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