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Fender Bassman 300 Pro - No output

G

glummoon

Guest
Jan 5, 2012
12
1
Oklahoma
#1
Recently my amp has powered up, and all of the controls on the front look normal with the exception of the Power LED. You can turn on the EQ, compressors, see input level via the LED, but there is no output. I am about to crack it open to see if there is something obviously blown, and I wanted to toss this out to the community to see if anyone had any ideas as to what might be going on with it.

Thanks in advance!

Jon
 
#4
I take a shot at this, my first question is when the amp is in stand-by, are the Led's glowing red? ... they change to green when you switch the amp out of stand-by, also there are some fuses by the power tube sections ...... did you check the mute switch?
There are no internal fuses on that amp, and thosep amp store 600+ volts in the caps ....so be very careful if you decide to open the amp up .... you really need to be pretty experianced to work on those amps ... IMHO
 
#5
I have checked the fuses in the back of the amp and they look good.

The LEDs do go from Red to Green when the amp is brought out of Standby, but today I am noticing that none of the tubes appear to be glowing. I am pretty sure they were the the other night when I first noticed the issue, but they definitely are not now.

I had a run in with the Tuner Only switch the other day(it being on and me wondering why there was no sound), so that was one of the first things I checked.

I believe these are the original Fender tubes that came with the amp, or an OEM Fender set, and I haven't had any work done on the amp since it was delivered two years ago.

Thanks for the help! I have a tribute show to play on the 14th, so any help in getting it back on the road is greatly appreciated.

>>>

When reseating the tubes I decided to try turning it on with just one pair of power tubes in place and an odd thing happened. All of the LEDs were Red, as I would expect, but when I came out of Standby they all turned green even though there were only two tubes installed. I am not sure if this is normal, or sheds any light on the situation, but I thought I would mention it.
 
#7
Indeed! I have seen pictures of the guts and at this point I don't have any plans of opening the innards on my own. It makes my 70s Bassman look like something a caveman built.

At this point I am hoping to get some information that could help a professional perform the repair quickly.
 
#8
I got up the guts to pull the amp out of the chassis today and found more fuses. I think I will replace all of them in hopes that one is actually bad. All of those 450v caps are pretty fearsome looking.

By the way, listened to the Monobrow stuff. Kept me going all the way through, thanks for the advice and the soundtrack for working on this.
 
#12
glummoon said:
I got up the guts to pull the amp out of the chassis today and found more fuses. I think I will replace all of them in hopes that one is actually bad. All of those 450v caps are pretty fearsome looking.

By the way, listened to the Monobrow stuff. Kept me going all the way through, thanks for the advice and the soundtrack for working on this.
Click to expand...

Glad the album came in handy :D.

Hopefully you can get the amp sorted out soon, curious to see what the problem is .
 
#13
I did get the fuses tested using a D cell and a multimeter. I will get in touch with the tech I have had recommended tomorrow and throw myself on his mercy.

In the meantime I have dusted off my old Bassman 135, and so far it has performed better than I could have hoped at practice tonight.

Thanks for all of the help, and I will be in touch with a resolution once he sorts it out.

Thanks again!
 
#15
Hey folks, just got my amp back from the shop and I am preparing to give it a test run. They said one of the transformer wires had been rubbing against a screw and had shorted out. Luckily the transformer didn't melt down and they were able to get everything up and working in less than 24 hours. They were surprised that no one got shocked and that the transformer survived the ordeal.

They said that Fender had put out a suggested modification raising some of the capacitors and resistors by an order of 10, i.e. some of the 47 micro farad to 470 and some resistors from 3.3 ohms to 33 ohms. This is supposed to combat some of the heat issues that the amp experiences. I am going to hold off on this until after the show, but I want to keep this amp until I am old and gray, so I will be getting it done.

Thanks again for all of the help, and I hope this helps someone else in the future.

Jon
 

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