The final part for the battery pack has finally arrived, the PCM boards. These modules protect the cells by cutting off the power at overcharge, undercharge & overcurrent. Each cell is connected individually on the right, 12v power appears on the left connections. These modules also ensure that all the cells in the pack are balanced.
A few modifications were required to the SMPS modules to make the power rails stable enough to run the Pi & it’s monitor. Without these the rails were so noisy that instability was being caused.
I have replaced the 100µF output capacitors & replaced them with 35v 4700µF caps. This provides a much lower output ripple.
There are also heatsinks attached to the converter ICs to help spread the heat.
Here are a few details of a valve amplifier I am building, using the valve related parts from a 1960′s reel to reel tape recorder.
This amplifier is based on an a Mullard ECL82 triode/pentode valve, with an EM84 magic eye tube for level indication.
Here the first components are being soldered to the tags on the valve holder, there are so few components that a PCB is not required, everything can be rats-nested onto the valve holders.
Progressing with the amplifier section componentry, all resistors are either 1/2W or 2W.
Here the valve holders have been fitted, along with the output transformer, DC smoothing capacitor & the filament wiring, into the top of the plastic housing. At this point all the components that complete the amplifier section are soldered to the bottom of the right hand valve holder.
Starting the wiring between the valves & the power supply components. The volume control pot is fitted between the valve holders.
The valves here are test fitted into their sockets, the aluminium can at the back is a triple 32uF 250v electrolytic capacitor for smoothing the B+ rail.
First test of the amplifier, with the speaker from the 1960′s tape recorder from which the valves came from. the 200v DC B+ supply & the 6.3v AC filament supply is derived from the mains transformer in the background.
Here the magic eye tube has been fitted & is getting it’s initial tuning to the amplifier section. This requires selecting combinations of anode & grid resistors to set the gap between the bars while at no signal & picking a coupling RC network to give the desired response curve.
Here both valves are fitted & the unit is sitting on it’s case for final audio testing. the cathodes of the ECL82 can be clearly seen glowing dull red here.
In the final section, I will build a SMPS power supply into the unit to allow it to be powered from a single 12v DC power supply.
Inside Electronics by Ben Thomson is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.