Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites

Steve (G3TXQ) posted a graph comparing Cecil’s (W5DXP) measurements of two turns on FT240-52 and FT240-K.

It is interesting to reconcile the #52 curves with Fairrite’s datasheets. A simple reconciliation is to compare results at the frequency where µ’ and µ” curves cross over. Continue reading Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites

Ferrite K mix

Among forum experts, there are ready recommendations for the ideal ferrite material (or mix) for a balun, often without knowing any detail of the application.

The ‘magic’ mixes include K. Perhaps they are devotees of Sevick.

Over some years I have searched for manufacturer’s data on K mix, and found only two references:

  • Amidon who give a very brief table summarising characteristics, inadequate for RF inductor design; and
  • Ferronics who give characteristic curves, albeit in less common format.

Problem is that Ferronics µi is 125 against Amidon’s 290… so their K materials are different.

One has hoped that an interested competent person might have made measurements of some samples from Amidon to give full characteristic curves, it isn’t that hard. Continue reading Ferrite K mix

LM386 audio power amplifiers

I tested a couple of LM386 audio power amplifier modules.

LM386tThe larger one was a kit using the DIP package, the smaller came assembled and used a SO package. Both cost less than $2 each posted on eBay.


They both deliver close to 3Vpk into an 8Ω load at 1kHz when powered from 12.0V. That is close to 0.5W out, but the SO chip cannot withstand the associated dissipation of 0.5W continuous output.

Both handle broadcast program quite happily at 0.5W peak, the chip temperature rise is 15° and 25° respectively.

Another Osram e-ballast bites the dust

I wrote in the fraud of energy efficient lighting – e-ballasts of frustration with green measures forced on us, measures that have replaced tried and true reliable lighting solutions with high tech low reliability solutions in a false promise of net energy saving.

Typically, the cost of repair and replacement of this unreliable technology is much greater than their direct energy saving, indeed much greater than their energy consumption of the life of the equipment.


Above is a ballast removed from a light this morning after 4 years during which it was hardly ever used… perhaps 10 hours at most… so the original capital cost of $80 for luminaire and fitting for 10 hours service gives an average cost of $8/hr for capital and about $0.01/hr for energy. Continue reading Another Osram e-ballast bites the dust

Inexpensive utility rechargeable 9V battery pack for test instruments

There is often a need for a 9V battery for portable test equipment (NNA, Noise Bridge, Low R meter, Power Meter etc). A solution is a 8 cell NiMH pack.

BatteryPack9VAbove, a battery pack made from two Hobbyking 4 low self discharge AA cells. The packs come with JR servo connectors, and the pins are rewired to use the -ve from one pack and +ve from the other pack to one of the JR connectors. The other wires are connected via a 3A Polyswitch for s/c protection. A short JR to 2.1mm DC connector is made from a JR extension cable and 2.1mm connector. Continue reading Inexpensive utility rechargeable 9V battery pack for test instruments

The fraud of energy efficient lighting – e-ballasts

In Australia, conservationists have led a push for replacement of a range of appliances that were in good working condition for more energy efficient appliances. For this reason, some types of appliance can no longer be purchased, or serviced with spares as required.

The humble flourescent light is one of those. Although still one of our most efficient lights, rivalled only by the best of LEDs, the push is on to replace the conventional magnetic ballast flourescent T8 flourescent with T5 lights, and in the interim, T8 lights with electronic ballasts. Continue reading The fraud of energy efficient lighting – e-ballasts

Review of Ceramica ceramic bearing fans

For some years I have used Ceramica muffin fans for low noise and long life. They use a ceramic bearing which is quieter than ball bearings, but longer life than sintered bronze bearings which dry out.


In the last month, I have replaced three Ceramica fans that have failed, one with less than a year’s service and two with less than one month’s service. Continue reading Review of Ceramica ceramic bearing fans