blues Jr Problem

[Snivly]

I made the mistake of plugging my BJ into 4x12 16ohm speaker cab...
Sounded great.. then it blew ... All tubes are lit...
R47 is clearly fried!... Is it possible someting else could have been damaged also ?
the fuse did not blow.... Can any one advise on the ohms value of R47?

[52 Bill]

I made the mistake of plugging my BJ into 4x12 16ohm speaker cab...
Sounded great.. then it blew ... All tubes are lit...
R47 is clearly fried!... Is it possible someting else could have been damaged also ?
the fuse did not blow.... Can any one advise on the ohms value of R47?

According to the schematic R47 is 470K ohms, but R47 is at the input of the reverb return chip. I don't think that this cooked from what you described you did.

Is the amp making any sound now? If you turn up the master and then listen to the speaker do you hear any hiss or hum at all?

Have you checked the speaker and wires?

[Snivly]

See below from another fourm...
"I'd guess that an output tube failed, shorted out, and blew the fuse. This often toasts the first power supply resistor, R47. Look for burns and discolored resistors when you open it up. Also check the two screen resistors, R35 and R36."

The amp does have a slight hum when i turn it on R47 is clearly fried
the schematic i have is hard to read...#0057275000 dated 4/20/01

[52 Bill]

See below from another fourm...
"I'd guess that an output tube failed, shorted out, and blew the fuse. This often toasts the first power supply resistor, R47. Look for burns and discolored resistors when you open it up. Also check the two screen resistors, R35 and R36."

The amp does have a slight hum when i turn it on R47 is clearly fried
the schematic i have is hard to read...#0057275000 dated 4/20/01

Sorry... I pulled up the latest version schematic which is rev-D. What version is your amp?

In any case the value of R47 on older models is 2.2K 2 watt flame proof. If this resistor opens up, it will cut off the voltages to the entire amp, and could cause the symptoms that you describe.

As for the fuse, is it the correct value? How loud were you playing? The output tubes may or may not be damaged, but a big current draw could have caused the resistor to overheat and open up.

[Snivly]

Thanks for taking the time to help with this ...
The fuse is the original stock fuse 2 amp and is still good
I had the amp cranked up pretty good... Master up around 8 and volume around 3...The schematic i have is rev-A... R47 looks like ... Fr 2.2 2W
Any idea where I could get that resistor ?

Thanks again
Tom

[52 Bill]

...The schematic i have is rev-A... R47 looks like ... Fr 2.2 2W
Any idea where I could get that resistor ?

Thanks again
Tom

Mouser, Digikey, Allied, Jameco, you name it. Anywhere really just be sure it is a 2.2K ohm, 2 watt flameproof resistor. I don't know where you are located, but if you have an electronics store nearby you may find that they carry RCA or NTE brand resistor packs. It's a pretty common value, but not something that your local Radio Shack would have.

Before you order, do you own a multimeter? Have you read the resistance of the resistor to see if it is open or not?

[Snivly]

Great ....
Thanks again, i have a meter and will check it out
Will let you know how i make out...

[Snivly]

Reading on resisitor R47 seems to be good
Readings on transformer seem good as well... any other ideas ?

[Feramentum]

Replace the resistor anyway. unplug power tubes and measure plate voltages. Make sure you have some. It's a push pull amp. tubes glow because its main power transformer supplying voltage to the heater element. Your issue seems to sound like its in the power tube stage. I have seen things look great till they get operational voltage and then they fall apart.