[Amps] Microwave oven transformer, mobile supply

[Larry Kayser]

Greetings:

I see some discussion in the last few days about using microwave oven 
transformers in power supplies for linear amplifiers.  I have some small 
experience along this line.

I recently acquired a new-to-me Jetta Diesel and I have been anxious to 
return to CW mobile.  During the winter in this area, when Jetta Diesels 
have to be plugged into start, I tried an experiment, a well charged large 
battery in the trunk and a 300W AC inverter, modern type, the plug into the 
block heater, a way to start the car with a 15 minute run on the inverter 
in cold weather.  (Where I park the car I have no AC power available, I 
live on a small island a mile off the mainland.  You can also run a battery 
charger off the inverter to charge the battery while travelling).

Looking at the inverter I decided to try and see if the inverter would run 
an ex Microwave Oven transformer so that I might use a single 813 in the 
trunk as the afterburner for a CW mobile station using a QRP rig as the 
exciter.  The transformer is loaded with a 275W dummy load of 
resistors.  The voltage rests at about 1650 V AC, dropping the resistive 
load 90% takes it up to only 1750 V AC.  I have run the setup for a number 
of trips of 75 miles each way with about 50% duty cycle.  The transformer 
does not get excessively warm and the high voltage AC is reasonably stable.

Just my experience.  I am currently trying to figure out how to regulate 
10V and 3.5A for the 813 filament off of a 13V or higher battery voltage - 
not much headroom....

The Microwave Oven that this came from was probably 15 years old, It was a 
junker and I did not make any note of the parentage....

Larry
VA3LK