10-28-2011, 02:15 PM
First off, be VERY careful checking your a.c. transformer!, high voltage from the secondary to the plates of the #84 rectifier is lethal ! To check to see if your a.c. trans is still good, you will need to use a variac to "slow up" line voltage from 0 up to full 120 v very slowly. You will also need a ammeter set to low scale to read the current being pulled by the transformer. The ammeter needs to be connected in series on one side of your a.c. line cord that powers the transformer with ac switch on (primary side of trans).
Remove your # 84 rectifier tube from the socket. With variac set at 0 volts, slowly up the voltage to about 25 volts ac, watch the ammeter, if it starts climbing beyond 1 amps... going on up as you slowly increase the ac voltage up higher, you have a bad transformer. On the other hand, if the ammeter doesn't climb as you up the the a.c. voltage from the variac up to full line voltage (120 v), your transformer is most likely still good. In that case, look for mistakes or other problems by carefully reading the schematic. Most radios pull around 1 amp max +/- a little current on the primary side when everything is working properly. If your trans is bad, you can lookup each individual tube and add up the total amperes (filament current) of all tubes combined in the set. Same with the 84 rectifier tube filament and plate currents. You can then determine what kind of replacement to purchase. Be careful working around the a.c. trans!!
Remove your # 84 rectifier tube from the socket. With variac set at 0 volts, slowly up the voltage to about 25 volts ac, watch the ammeter, if it starts climbing beyond 1 amps... going on up as you slowly increase the ac voltage up higher, you have a bad transformer. On the other hand, if the ammeter doesn't climb as you up the the a.c. voltage from the variac up to full line voltage (120 v), your transformer is most likely still good. In that case, look for mistakes or other problems by carefully reading the schematic. Most radios pull around 1 amp max +/- a little current on the primary side when everything is working properly. If your trans is bad, you can lookup each individual tube and add up the total amperes (filament current) of all tubes combined in the set. Same with the 84 rectifier tube filament and plate currents. You can then determine what kind of replacement to purchase. Be careful working around the a.c. trans!!
