Fuse Blown Bassman RI--Save me Skip from the Internet!!
Hey Skip,
Thank you for always saving me from the rabbit hole that is the internet, where I scour it for useless scraps of questionable ideas about harmonica amps! I really appreciate the excellent advice and information. I am so grateful to have such a phenomenal resource!
-I was recently playing at a Jam with my Bassman RI. I bought this amp used and it is 10-15 years old. It has a 5AR4 Groove tube for rectifier, 2 electroharmonix 6L6's for power tubes and the usual lower gain tubes for preamp.(These were added at some point from either of the two previous owners from the stock set up) I had the two resistors suggested on the "Bassman Chronicles" on this website, upgraded to allen bradley 1 watt just to be safe. I have not had the amp biased but my local tech remarked at how incredibly quiet this amp runs. It has no hums, buzzing etc at all. He thinks it runs very cool. It is about the most quiet amp I have heard. No issues with power, volume etc. It has always played great! I have owned this amp 1 year. I was playing last night and the amp sound stopped, the light on top went out. I always plug in with a surge protector. Surge protector was not tripped so I don't think a power surge happened. I checked the fuse and it definitely blew. I doubt the fuse was ever changed in the last 10-15 years.
-I have heard that the fuse blowing could mean an issue with the rectifier or one of the power tubes. David Barrett posted that he recommends having spare fuses in the rare event that a fuse blows. Is it possible that a fuse can blow because it overloads or is just too old? Or when a fuse blows, does it definitely mean I should look at the tubes?
Thanks as always for giving me solid advice from an expert!
Hey Skip,
Thank you so much for taking the time to answer my questions as always! You are a phenomemal resource to us crazy harp players. I replaced with a new fuse of the same value and turned the amp on for an hour (not playing) No problem. Turned on again and played hard for an hour, no issues at all. Played hard for 45 mins at an extremely loud jam where the amp is almost against the drum kit with guitar amps sometimes facing it. The amp was great as always. Hoping it was just a 15 year old fuse. I did swap out the rectifier for a brand new electroharmonix 5U4 that I had on hand. I will do as you suggest and turn on the amp with no power tubes and go from there. Thank you so much!
Hello Erik- Sorry for the slow reply. Yes, fuses can blow at times even though there is absolutely nothing wrong woth the amp. Put in a new fuse of the proper value and the amp works just fine. The most likely cause is a power surge at the AC outlet, but improper use of the standby switch can do it as well.
The fuse will also blow when a rectifier or power tube fails. I would guess that this is your problem. Put in another fuse, then turn the amp on without the power tubes. If the fuse doesn't blow, then there is a good chance that you have a bad power tube. If the fuse blows again, try it without the rectifier tube installed. If an amp blows fuses with no rectifier or power tubes, you're done. Call the tech.
One other Bassman-related item: take a look at the 470 ohm resistors that are soldered directly to the power tube sockets- a shorted power tube will often burn this resistor. If either are charred they will need to be replaced.