Rek O Kut Challenger Blowing Fuses

[leestavall]

Hi all -

Firstly, thanks so so much in advance for all of the great information you're always all so willing to share....

I have a Rek O Kut challenger with a Presto 1-D that works like a dream. We moved it to a new office this week, a 2 mile commute. When I plugged it in, it immediately blew the fuse. I went to Radio Shack and bought new fuses, but bought the wrong one. I stuck a 5 AMP fuse in, but it was the slow-acting variety and rather than blowing, it made the coil smoke.

I went back and got the right fuses, but it blows them as soon as I flip the switch.

So the questions:

-Any idea what's going on with my amp, and how I might repair it?
-Did I ruin it by sticking the wrong fuse in there?
-I'm happy to buy a new amp, but I'm completely ignorant about what I'd need. I read all of the time about people using stereo receivers, and I know that impedance matters, but that's all I know. Any suggestions?

Again, thanks all! I humbly await your trollish wisdom!

-AZ

[mratx]

Are you referring to the mains fuse, or a fuse that you have installed to protect the head? If it's the mains fuse, the most likely cause is a bad rectifier or output tube. You may be able to tell the bad tube by looking, but more likely you'll need to test them or swap in replacements (the fuse won't blow with the bad tube removed, if you want to try to find it that way.) The cause could be something else (fried output transformer, some other failed component), but in tube amps far and away the top cause of a mains or ht fuse blowing is a bad rectifier or output tube.

Mark

[leestavall]

Hey, thanks so much for the reply! Yes, I was referring to the main fuse on the front of the amp.

I replaced the rectifier tube (5Y3) and since Maindrag Music here in Brooklyn had 6V6s laying around, I replaced those too. At first, the amp stayed on for awhile, though I couldn't get any signal to the head (the meter showed signal passing through, but the head itself was dead silent). It eventually blew that fuse and now I'm back to blowing fuses as soon as I turn it on.

Any ideas as to what else I could try to fix?

Thanks in advance!

[markrob]

Hi,

Try pulling all tubes and see if the fuse still blows. If so, then the power transformer is likely shorted. If not, plug in only the rectifier. If that causes the fuse to blow, I would suspect a shorted electrolytic filter cap. Most likely, the cap closest to the rectifier. If the unit has never been re-capped, this is probably the issue.

Mark

[leestavall]

Thanks Mark! I think you've helped me narrow. The fuse blows as soon as the rectifier tube goes in. So next step is to replace that filter cap, yea? I suspect that is what's under the those 2 silver cylindrical things. Any idea where I can find replacements? I tugged a little on those things and they don't easily come out...

Man, I owe you lunch next time you're up in NYC!

[leestavall]

Update:

Attached is a picture of the Sprague Capacitor that's in the unit. See attached picture. Googling Sprague A-1546 doesn't yield much, though there does seem to be plenty of Sprague Caps on eBay. I'm not even sure how to get the damn things out of the unit, much less purchase the correct one and install. Any info would be so so appreciated!

IMG_0709.JPG

IMG_0708 2.JPG

[mratx]

That's a multi section can capacitor, the specs for each section are on the side of the can (the 10 - 450, etc.) The first value is the capacitance, the second is the voltage rating, like 10uf 450 volts. The figures (square, triangle, semi circle) represent different sections, the connections on the bottom will have the figures by the appropriate connections. You need to desolder the existing connections, and then there should be probably four metal tabs underneath which hold the cap to the chassis that you need to straighten to pull it off. You just need to match the specs to a new multi section can cap, like this one: https://www.tubesandmore.com/products/capacitor-ce-mfg-450v-10101010-f-electrolytic. The capacitance values need to match, but the voltage just has to be the same or higher (so a 10-475 would be fine.)


Mark

[Radardoug]

If the fuse blows as soon as you plug in the rectifier, then its not the cap. For it to be the cap, the filaments of the rectifier have to warm up.
But if the tube has a heater to plate short, that would do it. Or heater kathode short.

[leestavall]

But if the tube has a heater to plate short, that would do it. Or heater kathode short.

Thanks for this! Do you know I can test both of these scenarios? I'm not sure which is the heater, or plate, or kathode.

I think I'll order a new caps anyway since I know they've never been replaced.

[leestavall]

And, thank you MTRAX! Ordering that cap right now.