Ampeg Aurora Borealis (aka Jet)

[valvenator]

Some years back I picked up a nice Ampeg Jet guitar amp. The stenciled lettering on the chrome was pretty shot but everything else was in excellent shape, even the tolex on the cab.
Plugged her in and was really surprised by how clean and quiet she was, no hum or buzz, just pure guitar tone.
...that is till the last time. Played it for a few minutes when out of the blue the volume started to die and became distorted, not in a good way. Before I could hit the power button the fuse blew.
Opened the back and checked for suspicious looking caps and resistors and found nothing.
Pulled all the tubes and plugged it in, no problems. Thinking maybe the rectifier tube had given out, I tried a different one and again fired her up. As soon as it had warmed up the rectifier started glowing like the Aurora Borealis and the fuse blew.
I haven't messed with the amp since and have no need for it now and would like to sell it in good conscience.
Does anyone here have a clue what might be wrong with it? I think the problem is confined to the power section, so what could it be, bad caps, transformer (I hope not) or something else.
Like I said I didn't see any obvious burned out resistors or the sort. Any help would be appreciated.

 

[century tek]

Got a meter? It's a hobbyists best friend! Check the first filter capacitor. Find a tube tester and test the rectifier tube for shorts.

 

[tubeampking]

You won't necessarily see a shorted electrolytic, but if be willing to bet that's what it is. Change them all out...its way past time

 

[arts]

Definitely sounds like bad filter caps. Be careful though. When you hear it with new caps you might not want to sell it anymore. Keep in mind that this is coming from a guy whose house looks like a 60's/70's Ampeg dealership

 

[valvenator]

Thanks guys! I'll have a look at at this weekend. I was thinking that's what it was, but never pursued it further.
Just hoping it didn't take anything else out in the process.

arts, it's one of those things I don't use and want to downsize, but I'm afraid once I get rid of it I might regret it too.
Maybe if I sell I'll just sell as is, this way I won't have sellers remorse.

This is the third Jet that went through my hands, each from a different year with different tube layout. They each had a slightly different sound.
Many years back I also had a B15N I picked up cheap because it was "shorting out".
Turned out to be nothing more than a worn speaker connector. Sounded pretty dang good with guitar too.

 

[arts]

Ha,I know what you mean about downsizing.Unfortunately,where I'm located these models rarely come up for sale,so I guess I've become a bit of a collector.
The B15 is a great amp and I'll never part with mine ,a 1964 & 1970.
I think that,of all the Portaflexes (and guitar amps in general) the B12XT is probably my favourite. If you've ever tried one,it's quite the experience.
I have a pair of these,both 1965's,and both with their original Jensen Concert Series speakers.Playing slide on a Firebird through one of these is something I'll never forget!
Sold the Firebird.Duh.Talk about sellers remorse.....

In any event,you will get a far better price if it's working.Replacement caps are readily available at low cost,and are easily installed.

 

[valvenator]

To make a long story short, one day I was thinking how I missed the B15 and started scouring eBay.
The B12 came up and I was tempted but the prices were a bit high. I decided instead to give the Jet a try since I didn't need the wattage.
I think if I'd gotten a B12 my search would have ended right there and then.

I really liked the B15 but my brainiac idea was to replace that 15 inch bass speaker with a REAL guitar speaker.
I learned the hard way that those old alnico speakers were a huge part of the sound. Picked up a Fender branded JBL orange frame, forget the model. It was loud!!!!...but...
A friend needed a bass amp and I decided to sell him mine. After I put the original speaker back in I had second thoughts so I made him promise that if he ever sold it he would let me know first.
Dummy forgot his promise.

You know, another bass playing buddy of mine has a B12 he's not too thrilled with. I think I need to give him a call.