Help! Troubleshooting a Fender Bassman 70...

cuffdc

cuffdc

chicken n waffles
I'll preface this by saying I don't know if it's the amp, but the last two practices I've felt like my tone is extremely muddy. I got this amp probably around 2010 and I've never changed anything (including tubes) or taken it to a technician.

First, is there a quick way to determine if the tubes are going (it powers up, it doesn't have much buzzing, etc.). Second, should I just give in and take it to an amp tech?
 
Start with your output tubes and replace them. Tubes are typically good for 10K hours but if you start to get issues with noise, crackling, squeals, feedback, muddiness or low output, it is time. Also note that Output tubes have a shorter life.

Make sure to get a matched pair.

If this doesn't solve you issue, then take it to a tech.

For me, I like to mess with preamp tubes I would look at that next if you were having issues with noise and squeals - usually V1.
 
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Reviving this old thread. I did swap all the tubes. Even before I did that, I was getting some static sounds like a radio that was between stations. Not loud, sort of background. The funny thing is that if I banged on the top of the amp Fonzie style, it went away for a time. Since I changed tubes, I don't think it's the tubes. I'm wondering if anyone's encountered that sort of noise from a tube amp and if you did, what was the eventual resolution.
 
cuffdc said:
Reviving this old thread. I did swap all the tubes. Even before I did that, I was getting some static sounds like a radio that was between stations. Not loud, sort of background. The funny thing is that if I banged on the top of the amp Fonzie style, it went away for a time. Since I changed tubes, I don't think it's the tubes. I'm wondering if anyone's encountered that sort of noise from a tube amp and if you did, what was the eventual resolution.
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"The funny thing is that if I banged on the top of the amp Fonzie style, it went away for a time."

I wonder if your tube sockets are loose or, need a good spray of Deoxit.
 
Basic rule is make sure every input, speaker, etc. jack nut is tight (they ground through their connection to the chassis) and the tube sockets and tube pins are de-oxidized.

But, honestly, take it to a good vintage amp tech. Time and heat takes it toll on components like electrolytic caps and carbon comp resistors. A thorough overhaul should make it gig-reliable for years to come. I do a lot of my own amp work, even build my own amps, but I still have a guy that I take things to when they develop intermittent issues or if my kid is going to gig with it. I know the circuits inside and out, but he has seen everything that will, and does, go wrong in old amps.
 
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I have not experienced muddy sound in an amp related to tubes. I’ve only experienced strange noise anomalies. Bad preamp tubes cause all kinds of noisy anomalies IME. Replacing preamp tubes has gotten rid of noise anomalies in multiple tube amps for me over the years.

Generally, preamp tubes are cheaper than power tubes. I typically start by replacing preamp tubes. But, I’ve never experienced preamp tubes causing muddy sound.

In my limited experience, preamp tubes fail sooner than power tubes. My power tubes seem to last longer than my preamp tubes.

I’ve also experienced noise problems related to amp potentiometers. Those are usually pretty obvious because they change as the pots are tweaked. DeoxIT helps sort those problems out.

The muddy thing is weird. I hope I never have that problem.
 
So I figured I spray some deoxit on the connectors and make sure all the screws were tight. First thing I notice is that one of the preamp tubes was cracked. I imagine that would explain why I was not getting the volume I thought I should be getting on the amp the last few weeks. While I was waiting for the Deoxit to dry I decided I would check out the capacitors. Took off the casing and I think I'll definitely need a tech to replace at least two of the caps, as can be seen in the pic here.
IMG_0395.jpeg
 
It's more than just those two caps that need work. This amp looks long overdo for some routine TLC.
 
BuzzBaloo said:
It's more than just those two caps that need work. This amp looks long overdo for some routine TLC.
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Yes, they might be original. I have no idea. I got the amp around 2010 and have never had it looked at. Fortunately, there's a guy in the area with a great reputation who can do the work.
 
cuffdc said:
Yes, they might be original. I have no idea. I got the amp around 2010 and have never had it looked at. Fortunately, there's a guy in the area with a great reputation who can do the work.
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Probably should just go ahead and replace all of the electrolytic caps. Even if the others look ok, they're not far behind those in terms of falling.
 
Folks, I took the bassman to a tech who was highly recommended to me and that was a trip in itself. Great guy who operates out of the basement of his house with his wife and seven cats and who knows he may have grown up in that house. At any rate, he took that bassman 70 and replaced the caps and a few other things and, as he says, "marshallized" the bass channel so now I have basically two amps in one. It sounds beautiful.
 
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