Way back when the TV channels closed at midnight and you were left with a little white dot on the TV, when milk and pop was delivered to your door and no one had ever heard of the Internet I started my career in electronics, first as a lab technician then moved onto TV repair. Back in those days, valves were still in use and I had to learn how to fault valve TV's, radios and amplifiers (1983). For some strange reason valves grew on me, they represented a wide range of skills in producing for example a radiogram from the metal chassis, to the electronics, the veneered cabinets and intricate tuning mechanisms - it was all there plus that "valve sound"
I've managed to "keep in touch" with valves and the love still continues - I own a valve amplifier - a big beast and a joy to listen to and stare at - it's a bit like coming home to a real fire - something to stare at :)
So, along comes an opportunity to do something different, away from the world of I.T, little black boxes with flashing LED's and fans. A client asks if I know anything about valves and says he has a headphone amp that does not sound as good as it should. He drops it off and I try a few weeks of listening tests - he's right, it sounds harsh, no clarity. So a strip down and a peek inside reveals a few short cuts made by the manufacturer. Some I don't really understand why, like the 4 resistors wired in parallel or the very low-grade capacitors but hey ho, there is at least a lot of room for improvement.
So, the first thing to do is check it's current performance, for this we need a multimeter, function generator and oscilloscope. After this we will change out the 6 diodes for fast switching diodes, change those 4 resistors and replace with 1.
Get rid of the power supply capacitors and replace those with high quality Panasonics, the input caps don't really need to be there but as I'm not sure how this will be hooked up to external equipment, I'll replace with better quality and double the uF of the caps. The 4 output caps will be replaced with 2 1500uf caps, again, audio quality. I'll also check the ouput transistors for bias and comapre channels to see if they need matching up or replacing. Plenty to do and with all this snow currently around, the perfect chance to start playing