Amps Bassman challenge amp.

CapnDenny1

CapnDenny1

Student Of The Blues
I've been working a nice looking Fender Bassman for a couple months. It looks great, but it has been kicking my rear end trying to fix it. It had a problem where it worked fine for 5-10 minutes, then the tubes would start flashing, and the speaker started popping really loud. It put my bias probe ammeters on it, and they would start pegging the current. One of the difficulties is you can't leave it that way, so there is no way to troubleshoot it when it happens.

I've tried, new tubes, phase inverter coupling caps, tube sockets, bias adjustment pot, and lastly the output transformer. I suspected the OT from early on, but they are $120, so if I bought it and I was wrong, well I get to eat the $120. The other things were bad, or at least were due for replacement, but the OT is another matter.

So far it appears to be working, but maybe I just haven't waited long enough for it to happen. One of the first amps I worked had a bad OT that caused by a bad coupling cap and tube socket causing the tube to red plate. I fixed that problem but it had already damaged to OT. Let's hope I got this one finally!
 
CaptainMoto

CaptainMoto

Blues Voyager
Everything I know about amp repair can be captured on the back of a match book.
As I read this, It immediately brought to mind an amp repair vid I watched just yesterday.
Maybe there's a tidbit on the vid that you can use

 
JPsuff

JPsuff

Blackstar Artist
Maybe give this guy a try.
His specialty seems to be vintage amps and other vintage tube-driven electronics.

 
CapnDenny1

CapnDenny1

Student Of The Blues
I enjoy both of their videos. Unfortunately watching them fix another amp isn't too helpful.

I don't always agree with them, but they are two of the better ones.

Some of the other techs videos are not that good, and give bad advice, and are very opinionated.
 
JPsuff

JPsuff

Blackstar Artist
CapnDenny1 said:
I enjoy both of their videos. Unfortunately watching them fix another amp isn't too helpful.

I don't always agree with them, but they are two of the better ones.

Some of the other techs videos are not that good, and give bad advice, and are very opinionated.
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I was just thinking that maybe one of their vids would hit upon something similar to what you're experiencing and that you might glean some insight.

Unless it's something specific, the internet rarely supplies "one source" solutions but rather a variety of opinions/examples from which one can formulate their own solutions.

It's a scavenger hunt most of the time but the "variety of sources" method has helped me solve a variety of problems over the years.
 
CapnDenny1

CapnDenny1

Student Of The Blues
If you watch a bunch of them you can find a general process or method of troubleshooting a problem.

But you can't just watch videos and learn how to do it. You need to do it.
 
dvs

dvs

Green Mountain Blues
Not to hijack your thread, but since it seems to be heading in this direction anyway, @CapnDenny1 I wonder if you've run across either of these channels, and if so what do you think of them? I like to watch these videos once in a while - not sure why, but I find them interesting and relaxing; I don't have any aspirations to jump into amp building or repair myself (though I did accomplish a couple of mods or fixes from Psionic on my Blues Jr!), but I appreciate your insight.

Psionic Audio: https://www.youtube.com/user/psionicaudio/videos

Fazio Electric: https://www.youtube.com/c/FazioElectric/videos
 
JPsuff

JPsuff

Blackstar Artist
dvs said:
Not to hijack your thread, but since it seems to be heading in this direction anyway, @CapnDenny1 I wonder if you've run across either of these channels, and if so what do you think of them? I like to watch these videos once in a while - not sure why, but I find them interesting and relaxing; I don't have any aspirations to jump into amp building or repair myself (though I did accomplish a couple of mods or fixes from Psionic on my Blues Jr!), but I appreciate your insight.

Psionic Audio: https://www.youtube.com/user/psionicaudio/videos

Fazio Electric: https://www.youtube.com/c/FazioElectric/videos
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Those are my two favorites.

I'm partial to Fazio because she has a vary calm and personable way of explaining things. Psionic is good too, but he can sometimes come off as a bit condescending. That's not a deal breaker just more of peeve.

But if I want reliable info and proper procedures, both are excellent sources.
 
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CapnDenny1

CapnDenny1

Student Of The Blues
The psionic guy is a bit condescending. He does know his stuff. But he appears to be one of those guys who knows more than the original designers, and likes to make mods to the amps. I prefer to leave them stock. If your not happy with an amp, sell it buy a different one. There are so many great sounding amps. I just hate when people put different tubes in an amp, like a 12AU7 instead of a 12AX7, or el34 in place of 6l6. I also spotted his Master Volume on 10. A clear indication that his has all the answers. Not to be judgmental or anything. He must be charging $75 per hr, or more.

The Fazio appears to do good work, but she didn't really explain things. At least not in the video I watched.

But if you enjoy their videos watch them. They are both knowlegable, and aren't wrong.

I liked the psionic guy's argument about replacing the old original caps in the amp, which some don't want to do He said it's like you have a 1965 Mustang with the original oil still in it. That's something, as long as you don't intend to drive it.
 
JPsuff

JPsuff

Blackstar Artist
CapnDenny1 said:
The psionic guy is a bit condescending. He does know his stuff. But he appears to be one of those guys who knows more than the original designers, and likes to make mods to the amps. I prefer to leave them stock. If your not happy with an amp, sell it buy a different one. There are so many great sounding amps. I just hate when people put different tubes in an amp, like a 12AU7 instead of a 12AX7, or el34 in place of 6l6. I also spotted his Master Volume on 10. A clear indication that his has all the answers. Not to be judgmental or anything. He must be charging $75 per hr, or more.

The Fazio appears to do good work, but she didn't really explain things. At least not in the video I watched.

But if you enjoy their videos watch them. They are both knowlegable, and aren't wrong.

I liked the psionic guy's argument about replacing the old original caps in the amp, which some don't want to do He said it's like you have a 1965 Mustang with the original oil still in it. That's something, as long as you don't intend to drive it.
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Fazio seems to live by 2 basic rules when it comes to caps in vintage amps:

1. Always remove "Death Caps" (and replace the two-wire power cords with three-wire grounded).

2. If more than one cap is leaking (or bulging or singed), then replace them all.

I get the idea of hanging on to vintage components. But if they're damaged or otherwise compromised there's no point in trying to preserve them for the sake of nostalgia.
 
CapnDenny1

CapnDenny1

Student Of The Blues
So I ran it with new output transformer for about 10 minutes. I decided it was probably fixed so I went ahead and fully replaced the original OT. I only had it wired in, sitting on the bench. I decided to try it with a guitar. It sounded pretty nice for about 15 minutes. But the pilot light is out again? I just replaced it? The the tube current sense meters started jumping way up and down again, just like before! Insert your favorite explicative here!

So I switched it off and went and hid in my room! I picked a fine time to quit sniffing glue!
 
MarkDyson

MarkDyson

Blues Hound Wannabe
"Did you try unplugging it and plugging it back in? How about Control-Alt-Delete?"

Sorry. I know this had to be frustrating as all hell. :Beer:
 
CapnDenny1

CapnDenny1

Student Of The Blues
I spent last evening planning my attack.

No, it does not involve a hammer!

I am going to remove the power tubes, and look at the signals that would be applied to the power tubes. Perhaps the problem is the phase inverter? Or even further into the preamp. I've never seen a preamp be able to do this, but I am running out of likely candidates.

It's a clue that the pilot lamp failed again.

Only thing I am sure of is that this problem is going down!
 
JPsuff

JPsuff

Blackstar Artist
CapnDenny1 said:
I spent last evening planning my attack.

No, it does not involve a hammer!

I am going to remove the power tubes, and look at the signals that would be applied to the power tubes. Perhaps the problem is the phase inverter? Or even further into the preamp. I've never seen a preamp be able to do this, but I am running out of likely candidates.

It's a clue that the pilot lamp failed again.

Only thing I am sure of is that this problem is going down!
Click to expand...

You may be on the right track.
My informal investigation of your issue turned up quite a few issues with power tubes that were somehow related to preamp tube behaviors, specifically phase inverters.

Though no specific connections were demonstrated, the many references to power tubes and preamp circuits definitely warrants further investigation.

I know very little about the nuts and bolts of tube amps, but it just seemed that there were too many references to phase inverters to be ignored or dismissed as someone's shot-in-the-dark guesswork.

Good luck.
 
JPsuff

JPsuff

Blackstar Artist
CapnDenny1 said:
After

Untitled by Dennis Kelley, on Flickr

Untitled by Dennis Kelley, on Flickr

About a $0.50 part. It was part of the phase inverter circuit. I've never seen this failure before. But it looked exactly like several other failures I did see.

So I need to put the old output transformer, since there is nothing wrong with it. But as I said I have an old Ampeg amp that needs an OT.
Click to expand...

Man, you are one dedicated S.O.B.

Congratulations! :Beer:
 
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