I did. I learned my lesson with some resistors a few weeks back. I tested all of these prior to install. The first time I checked the drivers on the left, one of them showed up as "no component" but I retested and got a value, so I thought I'd just had not gotten the clips attached firmly. Now I'm betting the part had an internal issue. And since its been installed I can't return it for credit.
Well, take it out and retest. If you complain, they may be willing to send you a replacement
or issue a credit.
or issue a credit.
Here's the TL/DWR: it works now.
I spent several hours on this amp yesterday and I kept finding issues. Low/intermittent/non-existent voltages, mostly. I reflowed the entire junction edge on the amp card. I used a small screwdriver to push in the notch-locks on the terminal cups at the bottom of the card. I tested and retested values. I pulled the electrolytics and tested them. Following some erratic voltages I ended up replacing the differential pair on the right channel (still ok but weak compared to the new pair in the left channel), the drivers in both channels (very sketchy, some showing only "diode junction" values on the Peak meter), and the bias transistor in the left channel (still good, but I had replaced the left channel so I wanted it to match).
At this point there was exactly one original HK active part left on the board, Q704. I left it because the left channel worked perfectly. And the right channel still refused to show a bias value. I finally figured it out by comparing the resistance between pins 3/6 and pins 23/26, which should directly reflect where the bias pot was set. Left channel varied from low to 4.7k, but the right wouldn't vary outside of 1.2 to 1.4k. That reminded me of something.
Weeks ago the left channel bias had failed when the 3.3R resistor near the bias pot had failed, and replacing it brought back the left bias. While I was fighting this right channel bias issue I kept going back to that in my head but every time I tested the resistor in circuit it was dead on at 3.3R. Just for kicks I decided to swap the left and right 3.3R resistors to see if the problem transferred, and the problem vanished. It must have been a cold solder joint. I'd reflowed most of the board but not touched that thing, apparently.
The amp is biased dead center on both channels at 10mV and it sounds as clean as can be. There's a bit of AC hum which I'd bet is due to the ancient transformers. I doubt its worth sending them off for a rebuild, so maybe when I start on the case for this thing I'll just put some shielding in.
Im using an old pair of B&W DM602 as lab monitors, currently listening to Pink Floyd's Final Cut. The track "Get Your Filthy Hands Off Me" has a nice thundering jet effect in the middle that just took me by surprise. This is a good amp now.
Lessons learned: look for the simple stuff up front. Test resistors, verify solder, look for breaks, compare channel voltages with each other as well as the schematic.
I spent several hours on this amp yesterday and I kept finding issues. Low/intermittent/non-existent voltages, mostly. I reflowed the entire junction edge on the amp card. I used a small screwdriver to push in the notch-locks on the terminal cups at the bottom of the card. I tested and retested values. I pulled the electrolytics and tested them. Following some erratic voltages I ended up replacing the differential pair on the right channel (still ok but weak compared to the new pair in the left channel), the drivers in both channels (very sketchy, some showing only "diode junction" values on the Peak meter), and the bias transistor in the left channel (still good, but I had replaced the left channel so I wanted it to match).
At this point there was exactly one original HK active part left on the board, Q704. I left it because the left channel worked perfectly. And the right channel still refused to show a bias value. I finally figured it out by comparing the resistance between pins 3/6 and pins 23/26, which should directly reflect where the bias pot was set. Left channel varied from low to 4.7k, but the right wouldn't vary outside of 1.2 to 1.4k. That reminded me of something.
Weeks ago the left channel bias had failed when the 3.3R resistor near the bias pot had failed, and replacing it brought back the left bias. While I was fighting this right channel bias issue I kept going back to that in my head but every time I tested the resistor in circuit it was dead on at 3.3R. Just for kicks I decided to swap the left and right 3.3R resistors to see if the problem transferred, and the problem vanished. It must have been a cold solder joint. I'd reflowed most of the board but not touched that thing, apparently.
The amp is biased dead center on both channels at 10mV and it sounds as clean as can be. There's a bit of AC hum which I'd bet is due to the ancient transformers. I doubt its worth sending them off for a rebuild, so maybe when I start on the case for this thing I'll just put some shielding in.
Im using an old pair of B&W DM602 as lab monitors, currently listening to Pink Floyd's Final Cut. The track "Get Your Filthy Hands Off Me" has a nice thundering jet effect in the middle that just took me by surprise. This is a good amp now.
Lessons learned: look for the simple stuff up front. Test resistors, verify solder, look for breaks, compare channel voltages with each other as well as the schematic.
Thanks for the support guys, I couldn't have made it through this thing without you three, also OzarkHiFi, MarkTheFixer, and PB2.
To finish this off I should post up the BOM and a summary for this project, because I won't be the last guy asking all the questions about the rebuild parts or goofy issues.
To finish this off I should post up the BOM and a summary for this project, because I won't be the last guy asking all the questions about the rebuild parts or goofy issues.
Upon looking at Citation 12 schematics, there is CR5 and CR6 both bias double diodes, with a 0,01uF cap on them i have a good idea that those installed to or at heatsinks for temperature compensation,
Any idea of the type of diodes, double 1n4148 would do?
Were to install them?
My Cit 12 had all components removed!
Maybe a picture?
I see thermal cutouts parts on output transistors.
As per schematics, those aren't on pcb, they are on heatsinks i believe.
Thanks
Any idea of the type of diodes, double 1n4148 would do?
Were to install them?
My Cit 12 had all components removed!
Maybe a picture?
I see thermal cutouts parts on output transistors.
As per schematics, those aren't on pcb, they are on heatsinks i believe.
Thanks
Found at the bottom of a storage box of parts....
STB644 double diodes mounted on each heatsink with stand off.
They measures 1,28vdc forward reading.
The parallel 0,01uF is mounted directly under the amp at the multi connectors.