KLV1000 4amp fuse blowing on keyup

[loopy]

Hello. For some reason my KLV1000 decided to play up after months of working fine.

At first I thought I heard a popping noise, but the power output and SWR remained unchanged, so I continued using it. Shortly it happened again, but still no change in power, so I thought nothing much of it. Shortly after again just before the 4amp fuse blew, I was keyed up for about a second, and everything was still fine.. SWR <1.1, and running at full power.

Now every time I replace the fuse, it blows instantly when I key up. All tubes are glowing as normal on standby. I read another post on this forum that suggested removing the driver tube, as that sometimes fails. I did that, and it's still blowing the fuse on key up. I checked the diodes and a couple of transistors surrounding the fuse and they seem fine.

What could it have been that was popping and eventually blew? I thought nothing much of it as the amp was still giving out full power while something was slowly blowing up, right up until the second the fuse blew.

 

[TonyV225]

Capacitors will pop when they let go I would look at the tops and bottoms of the caps look for tan or dark crust or sticky fluid and or bulges /splits in caps.

 

[loopy]

Thanks for the quick response. I'll check them out. What I forgot to ask was, does it seem unlikely it would be the tubes? As i mentioned, while something was popping, the tubes were still giving full output, so I have a feeling they're ok. Even if they're not, money's no problem as replacements seem cheap, I just don't want to remove them unless i really have to. This tube stuff is all new to me, so I don't know if it would be normal behavior for tubes to make popping noises without losing power.

 

[loopy]

Ok, checked all the 450volt caps and some others, they looked alright.

EDIT: removed all tubes and the fuse still blows :/

EDIT2: It wasn't just blowing the fuse, it was blowing the crap out of it, like there was a direct short or something. I don't know how I fixed it, but I got it to not blow fuses without the tubes. Now with the tubes back in it seems to be ok again, hopefully for a long time. At this stage I can only guess that there was a short somewhere, and nothing is actually blown.

 

[loopy]

hmmm.. still seems to be happening once things get hot. This time I did smell something burning which was R8, 100ohms 2watts. I'll have to replace that with something bigger.

Anyone got any similar experiences? I'm not driving it any harder than I have been since I first got it. The tubes get super hot to the point where you can't touch them, but Im thinking that's normal. Any other ideas of what could be drawing too much current and blowing the fuse once it gets hot?

Reference: http://www.rmitaly.com/download/manuals/KLV1000-manual_rel_200.pdf

 

[liquidh8]

ever figure this out?

 

[loopy]

I hope so. I replaced the 2 watt 100ohm resistor with a 5 watt 100 ohm resistor, and the 4 amp fuse with a 5 amp.

Also one of the tubes stopped working, so I'm using the remaining 4 for the output and one I bought elsewhere for the driver.

Seems all good so far..

 

[Charlie Brown]

Everytime I ever had a tube amp that blew a fuse I would ALWAYS I mean ALWAYS turn the amp upside down and try running it upside down... If it ran upside down 10 times out of 10 it was a tube. Over time the lil specks flake off the filaments and will short out the pins at the bottom of the tube.....! When you turn the amp upside down the lil specks or flakes or whatever u call it would be at the top of the tube and wouldnt short out the pins...! If that makes sense... If not then Sometimes it was something else but most times it was a tube. No charge LOL This is not your case but then again it is possible that a tube may have done just that and caused the resistor to burn? Anything is possible?

 

[Beetle]

hmmm.. still seems to be happening once things get hot. This time I did smell something burning which was R8, 100ohms 2watts. I'll have to replace that with something bigger.

Anyone got any similar experiences? I'm not driving it any harder than I have been since I first got it. The tubes get super hot to the point where you can't touch them, but Im thinking that's normal. Any other ideas of what could be drawing too much current and blowing the fuse once it gets hot?

Reference: http://www.rmitaly.com/download/manuals/KLV1000-manual_rel_200.pdf

Why replace it with "something bigger"? The 100 ohm, two watt rating is what the factory specifies, as is the size of the fuse. Replacing with another value/rating is inviting fire, among other problems. You have to determine what's pulling enough current through that part of the circuit to cause it to dissipate more power than it's rated for.

 

[wavrider]

The first thing I look at when ever some one drags an amp over, be it an amateur amp, commercial built or home brew, I take the fuse out to look at the amp rating. Nine times out of ten if it has a high amp fuse in it I find PS problems.

If it blows a 10 amp fuse put a 20 amp in it to see if it works, run it till the smoke comes out of it.

Like Beetle said, going with a higher rated component in most cases is just asking for problems.

Now if the component is marginal at best for the circuit design, like a zener diode for biasing, then sure put a bigger wattage diode in there.

Hopefully it was just a bad tube, glad you got it back working and hope it stays working well for you.

 

[liquidh8]

Yeah man, glad you have it working. I was just working on a KLV1000, and was just curious if you got it fixed. good deal. what sorta power you getting out of it now with the replacement tube?

 

[loopy]

The first thing I look at when ever some one drags an amp over, be it an amateur amp, commercial built or home brew, I take the fuse out to look at the amp rating. Nine times out of ten if it has a high amp fuse in it I find PS problems.

If it blows a 10 amp fuse put a 20 amp in it to see if it works, run it till the smoke comes out of it.

Like Beetle said, going with a higher rated component in most cases is just asking for problems.

Now if the component is marginal at best for the circuit design, like a zener diode for biasing, then sure put a bigger wattage diode in there.

Hopefully it was just a bad tube, glad you got it back working and hope it stays working well for you.

Thanks. I understand what you mean, but I do believe if the same issue were to reoccur, the fuse would still blow, even if it is a 5 amp. I know it's 1 amp higher than the standard, but i can live with that

As for the resistor, it was still reading okay on the meter, but was starting to burn in the middle, after several months of... possibly driving it too hard, and learning how tube amps work.

I'm still new to tubes, but I'd say it may have been a bad one. I switched it on one day and let it warm up as usual, then after a few keys, the power dropped. I wasnt running it hard, and there was no noise from anything blowing up. one of the four output tubes simply stopped working.

Yeah man, glad you have it working. I was just working on a KLV1000, and was just curious if you got it fixed. good deal. what sorta power you getting out of it now with the replacement tube?

Thank you. The tube is still the same type, PL519, so still doing the same juice (1200 PEP). I have them popular Russian tubes I'd like to fire up, but the heater voltage is 40volts AC (straight from the transformer), and I'd need it reduced to 6.3volts to run them. Not sure how to go about that just yet..

 

[suzerain]

This amp is to be driven very lightly.

The max. recomended input power is 2W deadkey and 15 swing!!

Never ever drive this amp with another amp, in fact turn even your radio down. I'm working on one now that was driven with a 2 pill and that fried a number of circuits.