I have a SWR LA15 bass amp. I had to replace the power entry module, because it got shoved into the amp box. It took a long time to find the right power entry module. I finally found it, got it installed. Now, when I plug my bass in the input to play bass. Pluck the strings and nothing. Yesterday I plugged in my phone into the mix input, tunner input, and the bass input jack. It worked, but didn’t sound right at all.
Plugged my bass in again. After I noticed that with my phone I could hear some music.
I plugged my bass in the same three inputs as my phone. The same thing happened still no sound from my bass. I started to tap on the pickup. I could hear the tapping through the amp. I have some contact cleaner. So I sprayed each jack, and each of the potentiometers with contact cleaner. I still can’t play my bass through my LA15.
Would anyone be able to give assist me with figuring out? Why I can’t play my bass through a bass amp.
Another obvious confirmation: Does it work through the headphone jack?
Edit: Honestly, your description of “the power entry module…got shoved into the amp box” concerns me. Traumatic damage like that could have caused all sorts of collateral problems: a loose wire in a connector, a cracked circuit board, etc. etc. I repair and restore vintage vacuum tube (valve) radios, and working on amplifiers makes me nervous due to the high voltages and currents present inside the cabinet.
This is something a lot of people may not be aware of, especially with tube amps.
Back in the day I did a stint servicing microwave ovens part time and there was at least one, sometimes two huge capacitor associated with the magnetron tube. If you didn’t discharge it before working on the unit you would get knocked on your ass very quickly, or worse.
On the commercial microwaves there were SEVEN interlock safety switches to prevent people attempting to work on them if they did not know what they were doing but some people still tried to do a DIY repair without knowledge of what they were dealing with and in at least a dozen cases, I know of, people actually DIED.
I can believe that. I’ve heard about the capacitors holding electricity. When I started working on my SWR LA15. It had been unplugged for years. If I start something, but don’t have any knowledge of I’m doing. I’m surfing the net teaching myself what is going and why. My daddy didn’t have no stupid, dumbass, with no common sense period. I’m going to try the head phone jack in just a few minutes. Thank you
It still worked with the power entry module shoved inside. After I realized what happened. I did take it to an electronic repair place around me. They kept the power amp for about 6 months to a year. They did replace the power entry module. But, said that the fuse cap is on back order, which back in was 2019. They did say that my old fuse cap will work. Well today I can turn on the amp But, barely any sound I get.
I understand that you can literally fry yourself from working on amplifiers. Especially when the amp has a huge, heavy ass transformer, and big Caps to go with the transformer. Just remember to unplug it a few hours plus. Before, you think about working on it.
Ouch. You did everything right and you end up with an amp that works worse (i.e., doesn’t work at all) than before you sent it out. My sympathies.
I won’t attempt to troubleshoot it remotely, and I’ll bet that there are at least one or two competent amplifier techs here who could give you much better advice than I could.
Best of luck; I’ll be following this thread to see what kind of resolution you get.
Yep… I know little to nothing. But, I honestly think that it’s something really easy to fix. I don’t have any way to get to the shop. Nor do I have the cash to pay someone. So I have to figure it out by trial and error.
The transformer is one thing but really it’s the large capacitors you need to worry about. Capacitors, also known as condensers in some parts of the world, are what you need to worry about.
I would not trust the capacitors to discharge by leaving the amp unplugged for a couple of hours. Capacitors store electrical energy and can keep that charge for days, if not longer. You need to manually discharge them. Not sure how you would do that on a tube amp, but, as was mentioned before, there maybe someone on the forum who has that knowledge that will get back to you.
When I said about leaving the amp unplugged for a few hours. It’s was just an example from my f@#$&d up, twisted logic. I’m very happy that it was dead for a few years. If it wasn’t then I would have fried myself. I never knew what capacitors really did. But, I have had a few folks from different forums I’m with. I did know a little more about the transformers do. With my SWR LA15 being dual voltage. I really could have fried more than myself. Also, I don’t have a tube amp. It’s completely solid state energy. Each time I work on it. When I’m done for the day. I won’t touch for a few days maybe more. I have heard that tubes are easier to repair. I don’t care which one is easier to fix. I don’t want anything tube. I barely have enough cash to survive through each month. If I had to be replacing tubes. I think that I would quit. I’m going to check out the headphones jack. Even though I don’t have any headphones. I’ll try to come out the head phone jack and right into my other amp. Like I said earlier today. I will definitely try to remember to take a few videos of my SWR LA15, and post them.
This is one of my three basses. Along with my custom First Act ME80 Walmart Special guitar, and the two amps that I use all the time. (Right now; I’m playing Metallica with Dave Lombardo playing drums. Instead of Lars Ulrich.) My bass is a Rogue SX100B (my generic Pbass).
Okay, one suggestion if you are serious about working on the amp yourself: Google around for the terms “isolation transformer”, “variable transformer” or “variac”, and “dim bulb tester”. These are three things that you should consider having on your workbench. They won’t prevent you from roasting yourself, but they make it less likely to happen so long as you study up on safety practices and try to follow them. The iso transformer prevents a direct path between your amp (or other device under repair) and your house wiring. It can help prevent you and your test equipment from going up in smoke if you touch the wrong thing in whatever you are working on. The var xfrmr lets you bring up voltage very slowly on the unit so you can catch problems before applying full power. Likewise, a dim bulb tester (easy and cheap to build yourself) will flag a short circuit or other high-current draw problem before it has a chance to do more damage in the chassis. The isolation transformer is probably the most important IMO, but can be a little expensive to buy one off the shelf. The old-timer techs always preached keeping one hand in your pocket so you don’t allow an electrical shock to flow between your arms via the heart. But it’s kinda hard to work one-handed. In any case, best of luck.
Thank you for your support and input.
