The AM Forum

HEY GUYS...MY APACHE WAS WERKING OK FINE...BUT LAST WEEK,WITH OUT WARNING...LOST THE HV...SMOKED THE 5R4s, AND LOST THE MODULATORS,AS WELL...OK...I'M THINKING C1/C2...ALL SEEMS OK..ANY IDEAS...?....TIM...SK..

Sounds like you are on the right trail Tim. I had a similar experience just recently with a DX-100. First look for the obvious 'optical indicators'. I finished a Valiant that was giving me the peedoodles. When all was said and done, I found a carbon arc on the HV causing the fuses to blow. Pull the tubes and start at the power supply with an ohm meter. Obviously there is a greater load than what was designed. What I did was systematically removed all branches of the B+ until I notice the excessive load went away. Mine turned out to be a short in the modulator driver transformer. Keep us posted of the progress.

Tim,

When you said you lost the modulators, do you mean the modulator tubes were damaged?  If so, sounds like a bias failure.  Check to see if your bias supply is working and if you have the negative bias (~ -35 volts at the G1 connection of each tube; a failure in the driver transformer secondary will also cause this loss of bias to one or both tubes) at the modulator grids.  Loss of bias would definitely cause heavy current draw and tube damage.

73, Rodger WQ9E

Check the plate supply meter shunt....sometimes they short.

...YA...LOST THE EL34s...AND THE 5R4s...ALL THE INPUT I CAN GET FROM YOU GUYS WILL HELP...I REPLACED THE CAP FROM HELL,C49,WITH A HIGHER VOLTAGE RATING,AND PUT A FUSE IN LINE WITH PIN 2 OF THE 5R4..GOTTA DO THE 5V4 NEXT..JUST PROTECTION,SO AS TO BLOW THAT FUSE,INSTEAD OF HIGH CURRENT ZAPPING THE RECTIFIERS.....GONNA CHECK C1/C2,AS WELL AS FILTER CHOKE,AND I HOPE ALL IS OK WITH THE MOD TRANSFORMER...AUDIO TRANSFORMER WILL BE CHECKED AS WELL..BUT HEY,I HAVE NO MONEY IN THIS THING...IT COST ME 40 BUX,AND WAS RUNNING OK,BUT I'M SURE I USED IT MORE IN THE LAST 3 MONTHS,THAN IT HAS SEEN IN 30 YRS.......TIM...SK..

MY Dx-100 went on a fuse blowing spree a while back. Turned out the HV filter caps would short out when the HV was applied but they checked OK with the low voltage from an ohm meter. Just put some new axial lead caps under the chassis and life is good once more.