How to rebuild a Sun Audio SV-2A3/300B Triode Amp…

Article by Carsten Bussler (2A3Manaic)

I am regularly asked whether I know who offers a used Uchida and how much it should cost. The answer to the latter question depends entirely on the condition of the amp. I always strongly advise you to include an inspection and, if necessary, a rebuild by Robert Graetke. It is not uncommon for the device to be a (amateurish) DIY device where a beginner has tried their hand at the kit…
In addition, when rebuilding the Sun Audio/Uchida 2A3, it is easily possible to provide the option of operating the 300B (by simply switching the tubes) and to retrofit the top-accessible wheels for hum balancing.

This SV-2A3, for example, is to be rebuilt at the customer’s request because the current condition of the internal structure is inadequate and the power amplifier is to be upgraded in terms of quality and sound. The power amplifier is to be given a lower overall gain so that it harmonizes better with the preamplifier. The power amplifier will be equipped with Teflon sockets for the tubes, as well as the option of conveniently adjusting the hum from the top (see above). The signal paths are wired with pure silver.

Status quo – the somewhat wild free wiring before rebuilding the power amplifier.

Short process: “Uschi” is first completely gutted. Either completely or not at all…

Robert makes two extra mounting plates from Teflon to mount the octal sockets.

Start of assembly. The potentiometer for the hum control can be seen above the sockets for the end tubes.

Beginning with the wiring…

The internal construction is almost finished, the wiring of the signal path is done in pure silver. At the front/bottom you can see the very expensive V Caps (approx. 200 USD each), which are said to have a wonderful sound… Mundorf caps or similar will of course also work.

…and ready for commissioning and fine-tuning. You might think there’s “less” in the Uchida now – that’s deceptive, it’s just tidied up!

Done! It looks simple, but only a specialist and experienced Sun Audio / Uchida expert like Robert can do it so perfectly – I speak from my own experience. Many thanks for the photos, Robert!

Article by Carsten Bussler (2A3Manaic)