Concert head, burned up resistors - need help

[boxnife]

I have a 70's blackface concert bass. I turned the amp on without a load and didn't catch if for about 40 minutes. It seemed ok at first, but then smoked a little and gave up the ghost. I was told that the burned up part of the board is the resistors - the bottom 3 of the 4 blue resistors are burned. Can someone steer me in the right direction for parts? I will get someone else to handle the soldering if it isn't safe for me.

Here's some pics, any advice would be appreciated!!

[Oli]

Hi,

I'm just working on my Concertbass aswell. Here is a link for the schematics:
http://sunn.ampage.org/site/schematics/

I would take out the whole board to check it. Maybe the transistors are bad aswell but the construction is quite simple and it's no problem to get the parts (exept the f**** ON/OFF button).

Here is a link for the coulor-code of the resistors (sorry just in german but that doesn't matter):  http://www.tabelle.info/widerstand_kennzeichnung.html

I think all resistors are 10% tolerance.

Remember to be careful whatever you do with the open amp and electricity!

Hope I could help,

Oliver

[loudthud]

The schematic referenced by Oli is the later one. You can tell which version you have by the number and type of filter caps. The details are given in my post in the following thread.

http://sunnforum.ampage.org/index.php/topic,4369.0.html

[mckinnon audio]

  Hi there,sorry to but in,just curious,doesn't the older version have a Boost and Distortion feature that's foot switchable and the red knob version has just the Boost? Thanks,Mel.

[loudthud]

The whole Concert Series is a mystery to me and the schematics I have aren't much help. The one in this thread appears to be the newer model. Power amp schematic D1085. It  has the 5W resistors which should be 1.5K. It has the 15 ohm 1/2Ws and the diodes that form a protection network on the base of each power transistor. But the blue (flameproof?) resistors should be 22 ohm 2W. (Color code red-red-black-silver) Did they get so hot the red turned white?

I have an old Concert Bass fixer-upper that I got on ebay. Tested 9-28-74. It has an older circuit with the Distort control and footswitch. It's gonna take some work before it can be turned on. Some blown power transistors and wires disconnected. For resistors in the output section there are 910 ohm 2W and 22 ohm 2W. PCB layout is different from the one shown here. Schematic for this model is D1003.

[boxnife]

Where can I pickup the parts that I need for this?

[Isaac]

Just a comment: with solid state amps, there should not be an issue with turning it on with no load connected. The output transistors just don't pump as much current through, and are perfectly happy. So, unless there is something very strange about the Concert series (which is always possible), this was not caused by running it without a load.