04-07-2016, 10:33 PM
Another from the box of bits, a bench PSU for non 6.3v valve heater radio work.
I've donr a quick sketch up of the circuit diag in EasyPC, one or two of the componant values are to be confirmed but the basic layout is correct as best i can verify by tracing connections.
Inside, nothing fancy, but some early 80s power supply connections that then were considered the norm but would cause some anguish these days. The vero is split into two halves.
The LH side houses a switchable 1.8 / 2.5 volt DC heater output, using an LED and 22R resistor to take some of the transistor drive away and lower the voltage output, a BD131 heatsinked does the work. A double 4.3vac winding transformer with the outputs paralleled provides power.
The RH side houses a fixed 90vdc HT output which is suitable for most old sets. Of note, the 120R resistor in the AC supply was found to be badly blackened and needs to be replaced with a higher wattage device. I don't know what the original builder was thinking but a quarter watt resistor was just not going to cut it in this application. A 3va transistor with a pair of series wired 0-36 volt outputs provides power.
On the refurb list, cleaning up the wiring to the transformers, in this day and age of heat shrink tubing there is no excuse for bare terminals.
I've donr a quick sketch up of the circuit diag in EasyPC, one or two of the componant values are to be confirmed but the basic layout is correct as best i can verify by tracing connections.
Inside, nothing fancy, but some early 80s power supply connections that then were considered the norm but would cause some anguish these days. The vero is split into two halves.
The LH side houses a switchable 1.8 / 2.5 volt DC heater output, using an LED and 22R resistor to take some of the transistor drive away and lower the voltage output, a BD131 heatsinked does the work. A double 4.3vac winding transformer with the outputs paralleled provides power.
The RH side houses a fixed 90vdc HT output which is suitable for most old sets. Of note, the 120R resistor in the AC supply was found to be badly blackened and needs to be replaced with a higher wattage device. I don't know what the original builder was thinking but a quarter watt resistor was just not going to cut it in this application. A 3va transistor with a pair of series wired 0-36 volt outputs provides power.
On the refurb list, cleaning up the wiring to the transformers, in this day and age of heat shrink tubing there is no excuse for bare terminals.