Bigears
Manager of my own day
A few weeks ago I picked up a HK Citation 16A with a blown output fuse and a dead channel, well aware of the common issues with these amps. I’ve heard how nice these can sound when restored, so I set upon fixing mine and then making the usual upgrades after I got it up and running.
This one had vented a 10,000 uF filter cap on the bad channel which was responsible for the fuse blowing
I ended up replacing all the electrolytic caps as a preliminary service before diving in deeper. I know these run hot and I wanted good heat conductivity on the T03’s, so I cleaned and reseated the outputs
Amp runs fine now, pulls out of protection in 5 seconds and the heat sinks run about 50c at 50 mV, normal operation from what I can tell.
Only remaining issue is high DC on the right channel, even with the adjustment VR turned full, I can’t get the right channel under 85 mV DC. The left side zero’s out fine.
To diagnose the R channel DC, I’ve done the following:
Swapped VR1 from right to left boards to make certain it’s not a bad adjustment pot. This changed nothing. I will change these to 10 turn Bourns once I resolve this last issue.
Measured right driver board zeners:
CR3 10.06 vdc
CR4 10.08 vdc
At this point I’m thinking driver stage transistors have drifted, but I’m not familiar with the symmetrical complementary pair setup on this amp and would rather replace the correct driver transistors rather than doing a shotgun repair.
I’m thinking perhaps it’s Q1, which is the dual complementary pair, but I have no experience with these. Or is it the push pull pair, Q15 and Q17?
I know we have a few knowledgeable AK’ers with lots of experience on these amps, any/all help appreciated.
This one had vented a 10,000 uF filter cap on the bad channel which was responsible for the fuse blowing
I ended up replacing all the electrolytic caps as a preliminary service before diving in deeper. I know these run hot and I wanted good heat conductivity on the T03’s, so I cleaned and reseated the outputs
Amp runs fine now, pulls out of protection in 5 seconds and the heat sinks run about 50c at 50 mV, normal operation from what I can tell.
Only remaining issue is high DC on the right channel, even with the adjustment VR turned full, I can’t get the right channel under 85 mV DC. The left side zero’s out fine.
To diagnose the R channel DC, I’ve done the following:
Swapped VR1 from right to left boards to make certain it’s not a bad adjustment pot. This changed nothing. I will change these to 10 turn Bourns once I resolve this last issue.
Measured right driver board zeners:
CR3 10.06 vdc
CR4 10.08 vdc
At this point I’m thinking driver stage transistors have drifted, but I’m not familiar with the symmetrical complementary pair setup on this amp and would rather replace the correct driver transistors rather than doing a shotgun repair.
I’m thinking perhaps it’s Q1, which is the dual complementary pair, but I have no experience with these. Or is it the push pull pair, Q15 and Q17?
I know we have a few knowledgeable AK’ers with lots of experience on these amps, any/all help appreciated.
Last edited:
Right channel DC is stable at 2 mV and amp sounds great.
