21-09-2023, 11:02 PM
So an update after spending a week in bed with the flu. ( first in probably 30 years )
So the photos have labels/names, but here goes.
Front: this is what you will see. There are two seven pin minature valve bases still to fit for the 0B2's.
The large boxes are the main filter chokes. They are something like 2 Henries at 350 mA, ex equipment from a Royal Flying Doctor base station transmitter.
Rear: this is the back panel. It looks a bit complicated but its very simple really. The top of the chassis is two toroidal power transformers. They are wound in my normal super eccentric ratings.
The iron cores are 360 watt rated, but the traffos are overwound to achieve a mere one Tesla flux density, so they only run at maximum of 218 watts. They incorporate a screen winding of copper foil,
and an external flux band of Mumetal. Hopefully no hum !!!! ( he said, and held it to the light ).
In the centre of the chassis is the mains input socket, containing a master fuse in case something happens to my wiring, or the primary windings of the transformers.
Extreme left and right are standard circular aircraft connectors that will have the umbilicals to the main amplifier. These are rated @ 500 volts and 5 amps per pin.
Four fuses, one each for mains of each transformer, and one each for the secondary HT supply for each channel of the amp.
Top: pretty self explanatory really. The holes drilled in the hold down washers for the transformer go right through the centre of the traffo, through both insulating neoprene washers, and through the chassis.
I have found that even that bit of airflow will mean "about 20 degrees C " cooler transformers.
The two main electrolytics, each consisting of an F&T dual 100 + 100 uF 500 volt working. One each will be after the rectifier, then after the filter choke. There is another identical cap in each channel of the amp itself to restore decent impedance after the loss in the umbilical cords.
Under: self explanatory again, but front panel has the neon pilot lamp, and the on/off rotary switch.
Moving to the right we have the terminals for the completely potted chokes. followed by the terminals for the caps and the bias supply transformers.
These actually run backwards, I will feed them a dedicated 12 volts from the toroids into the 30 volt secondary, and use the primary to supply my power to the regulators, and hence the amp with bias supply for the output valves.
The rest of the mess is flying leads from the transformers and the wires that connect to the aircraft connectors.
All I have to do now is wire it together.
Some will notice four tall brass standoffs that will hold the turret tag strip containing bits n pieces of the PSU, diodes, minor caps and resistors etc. I still have to make that up, but its in my head being designed by the other me.
I try and lay these out to acheive minimum lead length and avoid any cross over points that would bring my minus 105 volts close to my positive 425 volt HT. I dont need push the envelope for the wire ratings.
Wire will all be 24/.2mm standard switchboard wire, as is the standard in Australia. So its rated at 250 volts AC and 7.5 amps current. It should be adequate. Maximum current is the heaters for the 5B/254's running in series, which adds up to 1.8 amps for each channel. Nothing too outrageous.
All comments welcomed, and ANY suggestions to improve something I have done. Nothing wrong with trying for perfection. Both in performance and servicability.
