Knight ka40 recap n
- Thread starter warriorfan
- Start date
cademan
Lunatic Member
Try and find out why it's dead first. A recap may not help if the fuse is blown or it has a bad transformer. At least see if the tubes lite up for a few quick seconds. It is a good idea to recap especially since it still has all of the original 50+ year old capacitors, and this will usually bring dead things back to life, but just make sure the transformers are good before you proceed.
warriorfan
Well-Known Member
Fuse is good and it has been fired up. I already rubbed all the markings off the full set of mullards that were in it not knowing the markings would come off. When fired up all tubes appeared to light up and then it squalled/hummed and i shut it down. I am taking it to a buddy's here in a bit and he is going to trace the power supply out for me. Thanks for the reply!
Here's a thread from our very own forum!. It contains a schematic too.
http://audiokarma.org/forums/index.php?threads/knight-ka-40-rebuild-help.697897/
http://audiokarma.org/forums/index.php?threads/knight-ka-40-rebuild-help.697897/
warriorfan
Well-Known Member
My searches on anything hifi have audiokarma added! Thx guys!
warriorfan
Well-Known Member
I tested only for continuity on the transformers and was good. Where does one recommend picking up caps? I have been on fleebay looking and see most I need in low quantities. Do I need to watch for certain manufactuers for certain ones and avoid certain ones? Also I was going to look at putting nice binding posts on the back and was wondering if I can eliminate the 16ohm and 4 ohm spot to clean up the back and the circuit at the same time? I assume the center channel on this just provides a signal that isn't amplified? Thx again!
warriorfan
Well-Known Member
Does someone have this schematic that is a bit more legible? Thx again.
warriorfan
Well-Known Member
warriorfan
Well-Known Member
Also I found this has a f31b9f rectifier in it and it calls for a 5ar4. Going to check on that now.
warriorfan
Well-Known Member
Disrequard the above as the b31b9f is a 5ar4 from what I see.
I usually get my caps from Digikey or Mouser but you can get them from other places too. Multi-section caps maybe Antique Electronic Supply or Jim McShane. You can also use terminal strips and individual modern caps if a multisection isn't available in the values you need. What I've done specifically with the leaded type multisection is just cut the original wires near the cap, land them on a terminal strip, and mount my caps right there. Just beware if this isn't inside a cover since there will be high voltage on the terminal strips. Maybe fabricate a little cover of some sort if its not covered and you can't locate them underneath.
Toasty wires look more like bad soldering than any real problem. Those old vinyl coated wires melt pretty bad if you overheat them while soldering. Its a kit, you're bound to find some questionable assembly somewhere in the mix.
Toasty wires look more like bad soldering than any real problem. Those old vinyl coated wires melt pretty bad if you overheat them while soldering. Its a kit, you're bound to find some questionable assembly somewhere in the mix.
warriorfan
Well-Known Member
Thx gadget73! I really would like to find the multi section caps and mount them topside like the oe caps were. The few threads I have seen where guys are workin on this amp there is talk of space being tight and moreso I have not seen any claim to have the amplifier fixed when done. I tend to get heavily into something when I undertake it and this amp has been no different. So I will more than likely beat my brains in, waste time and money and fry the amp or myself. Teaching oneself electrical egineering is costly! Sorry for the debbie downerness, but until I call this a win and have my first tube amp up and running I am just a guy in over his head. I appreciate all the helpful advice greatly all the same and I am game so I will give it a shot.
warriorfan
Well-Known Member
And those wires were burnt after I got it so I did whatever happend. I just can't read that schematic once I zoom in on it and it rotates with my tablet.
warriorfan
Well-Known Member
Yep I saw where guys are doing that. I really would like to not put this back together as it came. The case is butt ugly and brown! It acually reminds me of my cousins 62 4 door nova. I plan on building a bottom and leaving it naked so that beautiful glow accompanies the music. A couple kiddos running around here yet so I may make a cage?
+1 on rolling your own!
For a better schematic you could try sending a message to the guy who uploaded it, beemerbob.
I see no reason why you can't get this amp working, and I think it will be a rewarding experience for you. I am by no means an electrical engineer and I've gotten plenty of amps going. EEs focus on the "why", which of course is critical during design stages and testing etc, but in this case your focus is really the "what" as in "what the &*%$ is this wire supposed to be connected to?" and "what is the procedure for testing the power supply after I replace the filter caps" or "what sort of tools do I need to really do this right?"
For a better schematic you could try sending a message to the guy who uploaded it, beemerbob.
I see no reason why you can't get this amp working, and I think it will be a rewarding experience for you. I am by no means an electrical engineer and I've gotten plenty of amps going. EEs focus on the "why", which of course is critical during design stages and testing etc, but in this case your focus is really the "what" as in "what the &*%$ is this wire supposed to be connected to?" and "what is the procedure for testing the power supply after I replace the filter caps" or "what sort of tools do I need to really do this right?"
Paint, or from the hide of real Naughas ? If its paint thats easy to fix. The Naugahyde just is what it is. Either you appreciate it for the extremely vintage look that it is, or you put the lid somewhere that you don't have to look at it.
my Knight preamp was painted but in awful shape with a prior bad re-paint. I used solvent to get rid of most of the bad respray job and shot it with a nice silver-grey paint. No clue what color it was offhand, I just wandered through the paint aisle until I found something that looked good.
cademan
Lunatic Member
Those wires are not burnt because if they were, the wire along its entire length would be melted. Your hum is caused by an open filter capacitor not a shorted capacitor. Since you only turned it on long enough to hear a hum come up, you probably noticed that there was no smoke or a burned fuse. A shorted capacitor would blow a fuse, smoke, or both.
At least it is not shorted but is still bad and needs to be replaced. Those one's I circled are the one's I would start with. It looks like one of those has 4 individual capacitors inside, and the other one looks like it has 3 capacitors inside so for a total of 7 new individual capacitors or 2 replacement cans. Get these replaced and I'll bet you my left thumb that it will work and work well. After this, then maybe think about the other capacitors and maybe any out-of-spec resistors. Transformers are the least of your worries at the present.
Those old orange paper can capacitors are notoriously well known to not hold up well after a few years. Today's capacitors will outlive you and me!
At least it is not shorted but is still bad and needs to be replaced. Those one's I circled are the one's I would start with. It looks like one of those has 4 individual capacitors inside, and the other one looks like it has 3 capacitors inside so for a total of 7 new individual capacitors or 2 replacement cans. Get these replaced and I'll bet you my left thumb that it will work and work well. After this, then maybe think about the other capacitors and maybe any out-of-spec resistors. Transformers are the least of your worries at the present.
Those old orange paper can capacitors are notoriously well known to not hold up well after a few years. Today's capacitors will outlive you and me!
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century tek
Addicted Member
As cademan has mentioned, I think you will be pleasantly surprised when you replace those capacitors. The white one's underneath will also need to go except that they are not critical to getting it up and running first.
