Building Valve Amplifiers
If you have bought a kit and are experiencing problems, then we might be able to help. While we cannot guarantee it will meet the suppliers claims, which are inclined to be optimistic we should be able to get the best out of it accepting any limitations of for example the transformers.
What's Vintagetech's view on DIY Build Valve Kits?
The lowest cost route to valve amplifier ownership is to purchase a Chinese kit, we recently purchased a few of these for evaluation purposes. The ones we selected were low cost 'single ended' amplifiers using EL34 output valves run as triodes or pentodes (ultra linear).
With just minor modifications the triode amplifiers sound very good, with a nice flat response, and with some extra screening material incorporated in the build, have very low levels of hum and noise. Output power was just over 7 watts (RMS), a lot less than the supplier claimed, but then a single EL34 running as a triode would never make the claimed 13 watts.
The Boyuu A9 kit, uses the same output valve but running as a pentode, using the suggested circuit, in our opinion it doesn't sound good and the level of hum was totally unacceptable, however with some modification and again some extra screening results in a reasonably nice sounding 7 watts (RMS) amplifier.
What's the verdict?: The two we evaluated represent exellent value for money, and so long as you can live with the slightly DIY appearance and limited power are a good buy, but read below before you place your order.
How much experience is required to build a kit?
Building a valve amplifier kit might look simple and indeed if you can read and understand a circuit diagram and can solder you should be able to get one working. However, what is not so easy is getting it working as it should; it's all too easy to end up with an amplifier than hums, or oscillates or worse still oscillates at above normal hearing frequency. Unfortunately it will not sound good (at the frequencies you can hear) and worst still it could burn out your tweeters. If you buy a kit from a reputable supplier and it comes with a point to point wiring and component layout diagrams, follow them exactly, if the wires appear to go ‘round the houses’ then it will have been done for a reason so don’t be tempted to change it!
Warning: Please be very careful as all valve equipment uses high voltages that can be lethal. None of the kits we have built and reviewed so far have included information about safe mains and signal earthing, so do make sure you are confident in your understanding of the issues. And finally if the valves are exposed then those high voltages will also be exposed if the valves are broken, definitely only for use in a child free area.