HK 17 Repaired
Ya. I hate it too when threads are left open ended.
After another upgrade to the output board I shorted to ground and the voltage regulators finally gave out. It took months to resolve the issue with the 17 because I tried to do the work myself. I got most of the way there and in fact I was a c@#*$-hair away from resolving it on my own but in the end I caved and brought it in to a technician for a second pair of eyes.
First I rebuilt the whole power supply with new Fairchild regulators, Vishay Bridge Rectifier, my 4.7uf Blackgate cap to complete the board, and all Vishay Dale 1% metal film resistors. The Vishay 2W power resistors were only available in 5% at the time i ordered. There were a lot of involved steps with this that lead me to isolate IC4 as being blown open. A friend on DIY audio helped me through learning how and where to measure.
With all of that completed I inserted the Power board and it didn't turn on! After that point Dave (DShoaf) helped me most of the way in figuring out what to do next. I owe him a debt of gratitude for his help. Dave walked me through identifying the problem, which originated on the Output Board. My first step was to remove the relay and eliminate it as the problem, which I did and that was not it so I put it back in the circuit. Next was to check the decoupling caps 2 at a time (C2/C4 and C12/C14), left & right channel.
After the first 2 caps were removed the 17 powered on for 5 seconds and then shut down again. Thank god for the new V reg with short circuit protection. As Dave pointed out to me in his first post I should have replaced these first and maybe non of this would have happened. Just knowing the new Regs have circuit protection gives a hobbyist piece of mind against making mistakes, which i did a few times reversing polarity and shorting to ground.
I removed the next 2 decoupling caps and proceeded to check the voltages. As soon as I turned it on it powered up and R36 started smoking. I immediately turned it off. It ended up that Q15 & Q16 were blown so I replaced them and Q7 & 8 to match. I also replaced the coupling caps and all the resistors.
After which the preamp turned on again and all the voltages returned to normal, however, there was still some stray DC in the right channel that was causing massive static in the woofers and for the woofers to push out on the right channel. Out of shear frustration and the fact that Dave stopped answering my PMs I ended up replacing all the transistors in the right channel and electrolytics in the right channel. I turned it on again and still static in the right channel.
At this point I surrendered and brought it to a tech who told me that basically there was nothing wrong with it, he just didn't like all the oversized caps I had on it with bypass caps. He had some static on start up so He ended up removing all the over sized caps I had on the board and replaced them with Panasonics. He did not put the bypass caps back. All of my caps measured fine with no leaks. He asked me if I wanted him to put them back but since he had the 17 running I said just to put my Blackgate Coupling caps back. He then cleaned and lubed all the controls. Sounds Fantastic!
Within days after getting the 17 back I decided I needed a Back up pre. I needed to know for myself how a tube pre stacked up against the 17 so I auditioned a Audible Illusions L1 line stage that my friend was selling. A single ended triode, dual mono tube amp that matched with the HK19 sounds incredible. The difference between the 2 preamps are completely different. The AIL1 is in a different league. Now the 17 is my back up pre.
I learned a lot from this project. Most notably, 1. resistors are as equally as important as the caps if not more. The noise floor and depth of sound stage increased dramatically with the upgrades. 2. Good voltage regulators & rectifiers are also essential. 3. Don't increase capacitance in the audio signal or bypass the audio signal, especially if its already inherent in the circuit design just by better signal caps. 4. Although capacitors do have sound signatures the best capacitor in the world will not add up to more than the sum of the circuit design. The circuit design is the most important element.
I think I will complete a few more upgrades like all the resistors in the phono stage and I may still look for some Blackgates for the output board signal caps but the 17 will not serve main duties for me anymore. Its not entirely fair to say the AIL1 is better but different in a way that is better. Perhaps I will enjoy inserting the 17 back in every once in awhile.
Currently I am changing all the resistors in the 19 and will post to that forum again soon.
) is going to make the sound stage seem bigger. :thmbsp: This board is stacked!
