Powering up the SW-3 (again)

After discussing with my buddy Eldon, I have decided not to use the voltage divider approach to power the filaments.  They are all wired in parallel and the risk from one of them opening up and thereby taking out the entire set of tubes is too great, not to mention the royal pain in the tush finding a 1.15 ohm 15 watt resistor will be.  I decided to order a 2.5 volt 6 amp transformer from Mouser for $13 today and will use it to power the tubes.  The other option would have been to rewire them all in series and use a voltage divider to come up with 7.5 volts from a 12 volt source.  At least if a filament opens up we power everything down, plus the voltage divider would be easier to construct without having to locate 15 watt resistors.

I love a few select old pieces of equipment, but powering them can be a pain in the empennage.  I have a couple sources for the B+ 135 volt supply, so we should be good to go once the transformer arrives.

Meanwhile, I am on the lookout for an old National "doghouse" power supply for the SW-3.

New receiver!

After a couple years of looking, I have located a National SW-3 receiver that is in good shape. 

It came with a couple sets of coils, a bandset coil set for 80 metres and an unknown coil set that was hand-wound by a previous owner as well as two sets of empty coil forms for my own hand-wound coils.  Subsequently, I have obtained a bandset coil set for 160 metres.

I am now looking for a period power supply, preferably one of the National "Dog-House" power supplies.

My SW-3 is one of the earlier version 2 receivers.  It has a pair of 58 valves (tubes) and a 50 valve (tube).  The filaments are 2.5 volt and the B+ is anything upwards of 350 volts though the National power supplies typically supply around 135 volts.  Meanwhile, I plan to locate a nice high voltage lab supply to be able to test this little beast out.