Ampeg Portaflex Problems

melkinsbass · #1 08-05-2010, 09:24 PM

I just bought an Ampeg B-12-XT off of ebay and it doesn't work (contrary to what the seller stated). They left the tubes in the chassis when they shipped it, and a couple of them fell out and were rolling around. The looked okay, so I put them back in. I fired up the amp, and it won't stay on; it keeps blowing the fuse (there was also a slight smell of something burning. Fuse?). I replaced the tubes that had fallen out (both 7027A's and the 5AR4), and the same problem occurred. It stayed on longer this time, but there was a popping noise and the 5AR4 started to glow really bright and then seemed to flash. I thought I smelled something burning, so I turned it off. Any ideas about what's going on? I contacted the seller, but haven't heard from them. Thanks.

coreyfyfe · #2 08-05-2010, 10:36 PM

These amps are really easy to open up, so if you're really careful about it, it's easy to give a quick visual inspection. You might have a fried component or short somewhere in the power section that is causing the arcing in the rectifier tube and causing the fuse to blow. If you do decide to do this, be very cautious, and don't touch anything on the inside. It's certainly work best qualified for a tech, but if you can see something discolored or burnt and can photograph it, it's likely someone here can identify the component and tell you what the issue is.

JimmyM · #3 08-05-2010, 10:43 PM

thanks johnk for telling me how to do this:

take all the tubes out, and put a fresh fuse in it, then plug it in and turn it on. if the fuse blows, you have a problem in the amp itself. if the fuse doesn't blow, try it with only the rec tube in it. if it blows, it's a bum rec tube (honestly, i think this will be your problem). if not, put all the other tubes in there. then if it blows, you'll know you have one of the other tubes on the fritz.

metalmariachi · #4 08-05-2010, 11:50 PM

Follow Jimmy’s advice.

MM

Beat me to it Jimmy LOL

melkinsbass · #5 08-06-2010, 07:47 AM

Awesome! Great advice; I'll try that this afternoon. I don't think it'll be the rectifier tube; this would be the 2nd one. I'll let you know what I find out tomorrow. Thanks!

melkinsbass · #6 08-06-2010, 10:39 AM

So, I pulled all the tubes out and turned it on: no problem. I put the rectifier tube in: no problem. I took it out and put the power amp tubes in: no problem. With the rectifier and power tubes in, it starts to pop and I smelled something burning so I turned it off. The rectifier seems to glow really hot with the power tubes in. I have no clue what that could mean. Any ideas?

JimmyM · #7 08-06-2010, 12:32 PM

maybe a bad power tube? i don't know...you pretty much tapped my knowledge...but i'll bump it for the smart guys.

melkinsbass · #8 08-06-2010, 12:38 PM

The rectifier and power amp tubes are new. It does the same with the old ones.

aborgman · #9 08-06-2010, 12:47 PM

Quote:

Originally Posted by JimmyM

thanks johnk for telling me how to do this:

take all the tubes out, and put a fresh fuse in it, then plug it in and turn it on. if the fuse blows, you have a problem in the amp itself.

In that case your problem is a short somewhere between the wall and the rectifier tube - sadly likely to be the power transformer.

Quote:

Originally Posted by JimmyM

if the fuse doesn't blow, try it with only the rec tube in it. if it blows, it's a bum rec tube (honestly, i think this will be your problem).

Or a shorted cap or resistor somewhere in the power supply down line from the rectifier tube.

Quote:

Originally Posted by JimmyM

if not, put all the other tubes in there. then if it blows, you'll know you have one of the other tubes on the fritz.

Or the output transformer, or...

http://paulrubyamps.com/info.html#FirstPowerUp

Has a pretty good "first power up" procedure to avoid destroying things unnecessarily.

melkinsbass · #10 08-08-2010, 11:15 PM

Well, one of the wire going from the rectifier socket to a diode had come undone. Looks like poor soldering. I re-soldered it and no more problems. The only issue left seems to be that the output is kind of quiet. I have a 35 watt tube guitar amp that's way louder. I'm not sure if some other connections aren't so great or what... The good news is that the tone is awesome! I just need to get it a bit louder so I can use it on guit*r gigs.