Nuts and Volts - March 2015

heating and such).

If the "no-load/load" voltage difference is negligible (<0.1 VDC), try adding a filter capacitor (start with a 470 µF electrolytic — watch the voltage rating of the cap!) paralleled with a 0.01 µF mica or polyester to filter out high-frequency hash that may be on the DC output feeding the clock. This may give you the stability you're looking for as most — if not all — warts are half-wave unregulated types with very minimal filtering to begin with. Adding more filtering (larger electrolytic) and bypass (small value) caps to the DC output greatly improves their overall stability and cleanliness of the DC output voltage.

Finally (as you already know), having a regulator between the wart and your device guarantees a rock solid DC source, as long as you don't pull too much current from the wart.

Ken Simmons Auburn, WA

[#2153 - February 2015]

Diode Decision

Can you PLEASE indicate which germanium diode would best fit this SW radio? Either a 1N34A or 1N60?

#1 Both diodes — 1N34 and 1N60 — are germanium diodes, and both are of similar physical size. The important thing is that this diode family has the smallest forward voltage characteristic, which is important for rectification of small voltages. They both will operate at radio frequencies. The forward current rating and the reverse voltage characteristics are unimportant in this application.

Bottom line: Either one will work in this application. My personal choice would be the 1N60 because the documentation available for this device is superior, with V-I curves to show the typical forward voltage characteristic. Peter A. Goodwin Rockport, MA

#2 Either should work well. Both have a conduction knee starting around 0.15 or 0.20 volts. The IN60 — being slightly newer — probably has more tightly-controlled specs. Here’s a source for diodes and their specifications: http://store.american- microsemiconductor.com/1n60.html and http://store.americanmicrosemi- conductor.com/1n34a.html. BT W, for better Q of the tuner, connect the diode to a tap on the coil.