Audiolab 8000a. 

The venerable 8000a can be split into pre and power amps relatively easily. Sockets are already provided, so it’s a case of removing two buffer resistors to remove the internal link between pre and power amps and adding two input caps to block any DC going to the power amps. It is also relatively easy to plumb in a relay in parallel with. The main delay circuit to add an 8sec mute to the pre out. Finding a relay that fitted the circuit board proved impossible, so I had to plumb in a larger relay. You also have to install the power for the relay from the main delay circuit.

The photos show the finished article with the white blocking caps and relay visible in the topside photo and power supply cable underneath.


Bush VHF 66 Radio 

This radio has been restored and a Chromecast Streamer added. The vhf section of these radios is very decent, especially with a good aerial, so well worth restoring. There are twin Celestion speakers, and a supposedly electrostatic tweeter. The tweeter had failed in this case, as happens often, and as the twin speakers have reasonable hf extension it has not been replaced.

The magic eye was replaced and glows away prettily without really helping the tuning process. The streamer I’d connected internally to then gram input, so the piano key switches are used to switch between stations and the streamer.

WAD 300b Stereo, Pre2 and Phono 2 Upgrades

I’ve built four WAD 300b stereo amplifiers and serviced many more. One of my own amps is a WAD 300b stereo too, so you can tel I love the sound. img_4137An upgrade for the Wad 300b stereo I’ve now done on six 300b stereos is to add an additional choke to the power supply for the input section. This improves an already great amp, providing more bass slam, detail and dynamics. The owner brought along his Pre2 and Phono 2 for upgrades too.

The Pre 2 had been converted to a cathode follower already, which overcomes the original design’s hum issues. So this time I increased the size of the power supply choke and converted the power supply to a pseudo mono set up. For phono 2 I added cathode bypass caps to the first valve.

Overall results are a very nice improvement in SQ for the system.

Conrad Johnson PV12 Phono Preamp

This nice sounding pre came in for conversion to remote volume control. A small remote module was installed internally, and a 9v regulated power supply made to take power from the heater circuit. The original Alps Black Beauty pot was replaced with a TKD motor pot, one of the best-sounding pots around. Finally the remote infrared sensor was N stalled to replace the power on led, to negate the need to drill the front plate. The finished unit works well and, most importantly, sounds great!

Plinius 8150 Output Stage Converted to Use Hypex Modules

This Plinius 8150 had blown one channel of its output stages. The problem in repairing it was that the J Fets see are now obsolete-the last pair I found sold for £150! So I converted the output stages to use Hypex 400 watt per channel Class D modules. These sound great and are a big step up from the original output stages. In fact, if I wasn’t into valves I’d probably use a some myself . Very detailed and grain free, they’ve com a long way since the early days. Add that to cool running and low power consumption and you’ve got real 21st century amplification.

Below the output stage is under test.

Now the preamp stage has been reinstated.

And finally the finished amp.