new to forum, static like sound at all volumes

[oregonblues]

I just bought a fender bassman ten, the later model with a mid knob and advertising 70 watts.

The caps LOOK good, no messages from the interior

The tubes LOOK good, no whitecaps, no burnt bases

The tap test is OK I guess, the first AX7 is a little noisy but aren't they all? (noobie)

What should I try on my own to eliminate the low level static sound I am getting?
It is present at all volume/master settings, all 4 inputs, only when an instrument is plugged in.
I opened it up, made sure I wasn't standing in a puddle with lots of metal jewelry and rings on, and blew air through all the pots, looked at the solder joints and wiggled stuff with a pencil. While I had it open, I replaced the power cord (it was missing the ground prong)

The only other tube amp I have ever owned is my Blues junior and it is going on 10 years old without a single problem- I love that amp.

I am hoping this bassman will be a decent bass practice amp and am looking for a rhodes to go with it eventually. I heard one played through one of these amps and have been thinking about copying that setup since.

Thanks in advance, looking forward to possibly getting into doing some mods someday, I have a basic electronics understanding and enough common sense to know I don't know enough to do anything more than just the basic stuff. maybe someday. It looks to me like I found a good forum to start up with.

[km6xz]

What type of sound? With the master volume down, there should be no signal from any of the 4 inputs and any noise that might be contributed by the preamps and tone circuit. The confusing point is that it occurs only when a guitar is plugged in. There is no jack or input muting function so you might have to look somewhere else for the problem. Are you using any outboard powered united such as peddles at the input?

[akimball442]

I just went through similar troubleshooting with my Twin-Reverb. Tube sockets can make all sorts of crackling noises, I've run across that in the past. My most recent crackling turned out to be a loose heater wire on one of the tubes, and it drove me nuts finding it. Check all of the solders using a chopstick or something similar (insulated) and poke all of the connections. The old Fenders built on the 'paper' board can do some strange things.

[oregonblues]

What type of sound? With the master volume down, there should be no signal from any of the 4 inputs and any noise that might be contributed by the preamps and tone circuit. The confusing point is that it occurs only when a guitar is plugged in. There is no jack or input muting function so you might have to look somewhere else for the problem. Are you using any outboard powered united such as peddles at the input?

Sorry for the confusion, it does make the sounds without an instrument plugged in. My best description is like radio static, or like a noisy pot that just doesn't stop. The amp sounds great otherwise, nice range of tone with the active jazz bass I play most. I think I will really like this amp if I can get it to behave.

[txstrat]

The tubes LOOK good, no whitecaps, no burnt bases

Does the noise go away when you pull the tubes? Have you changed the tubes for know good ones?

[überfuzz]

I've encounter the same kind of noise. Could be a bad tube, tubes can be bad even if they look good. The silver is mostly there to reveal cracked glass.

[oregonblues]

I am going to try the new tubes this next weekend, I don't have a good 6L6 but I have tried the others and they were fine but old, I will keep them but I am going to replace them too.

talking to some local more experienced tube owners, it looks like I have a pretty good chance of fixing it. I even found out that an old friend of mine once played bass through this amp helping the owner audition drummers and it was known to be a good rocking amp just a few years ago, he doesn't remember any problems with it and even tried to buy it.

thanks for everyones help, I promise to post results when I have them.

[txstrat]

For an easy testing you could pull the preamp and PI tubes. If the crackling stops it was either of them.

[oregonblues]

For an easy testing you could pull the preamp and PI tubes. If the crackling stops it was either of them.

I didn't know I could do that! I would have thought that just pulling tubes would make the amp inoperable, unless replaced with a known good tube.

So... I pulled the 2 preamp tubes and the noise continued, but when I pulled the inverter tube, no noise. Is that the answer? Should I just buy the 1 tube first and hope it does the trick?

[txstrat]

You could try to interchange the PI tube with one of the preamp tubes. If the hum comes back it's likely not been the tube. Unless the other tube is faulty too.

[oregonblues]

You could try to interchange the PI tube with one of the preamp tubes. If the hum comes back it's likely not been the tube. Unless the other tube is faulty too.

the PI is a different animal, same base, same size but a different number on the tube. I wouldn't want to do that would I? Again, I am a total Noob with tubes, it's not like puting a 40 watt bulb in place of a 60 on the front porch is it?

[txstrat]

If the tube reads 12AX7, 12AU7, 12AT7, 12AY7, 5751, 7025, ECC83, ECC81, ECC82 (I'm sure there are some more) you can interchange them for testing purposes with no risk to damage your amp. The tubes I mentioned above have the same pinout but a different amplification factor. You can indeed use the light bulb analogy.

[oregonblues]

I tried the swap on the tubes with a borrowed 12AX7 and got noise after swapping all 3 tubes out individually. Next suggestion was to let it sit and warm up for awhile, an hour or two, and then play it for awhile and see if it would blow up or not. It worked as usual, noisy as usual, and I shut it off. Next day, all I could get out of it was heat and lights, no sound.

It's off to the shop. I am paying for the full meal deal, full caps, tubes, blackface conversion, and a change in the circuit that will allow a proper bias on the power tubes. I get all the good tubes back, we aren't going to touch the speaker cab until we hear it with the originals, if it will work for now I'll give the oldies a chance, if not I can try a few different cabs at the shop and that will get done before I bring it home.

I am glad I got it for a song up front, I am going to be into it for a bit by the time I have it plugged in again back home. I could have bought a decent new amp for the same money, I could have bought an outstanding new amp for the cost if I end up doing new speakers too, but instead I have a really cool old amp that I am hoping will sound great for a really long time and do everything a brand new amp will do plus hold it's value into a few more decades, it already has over four of them and it doesn't even make noise right now.

[txstrat]

Good call IMHO. A decent "vintage" amp is always the right choice.

[Euthymia]

Those can be great sounding amps with a bit of modding, which it sounds like your tech is going to do.

I bet they'll also be replacing the plate resistors in the PI (likely source of your constant crackle).