76 Concert bass wired wrong

[animosity^2]

I have a '76 red logo Concert Bass that I bought off a friend something minor fried inside...  He let someone who he thought to be good at electronics check it out, and I'm pretty sure they removed the power amp board and messed up the wires when it was put back together.

There are tons of connections on the board and I was wondering if anyone could help a guy out with a color-coded schematic or pictures from their working rig...

I would name my first-born after anyone who can help me get this thing working again!

[Isaac]

Well, if you were in the Willamette Valley, you'd have a deal!

[animosity^2]

Isaac is a storng name for a baby boy, help a guy out!

[Isaac]

Tough to do long distance. I can't see the fried components, nor trace the wires. The power amp section is different than the one in my older Concert Slave, I think. I really don't see what I can do for you.

There's a Concert Bass schematic on this site, here: http://sunn.ampage.org/site/schematics/concertbass.gif

That might help, if it's the right model.

Edit by Loudthud: Corrected schematic link

[animosity^2]

there are 10 wires coming from the transformer to the power amp board, all the way to the left (if facing from the front).  Immediately jumping from 4 of those go wires to the 2n3055s.  I think most of my problem is there.  There are a few misc. connections on the front and rear adges and a couple on the far right edge of the power amp board.  All I am wondering is the color code...  The schematic is for a different era Concert bass, probably newer looking at the way the power amp board is done.

There are a couple of blank spots as well, I would presume for test functions.  If anyone has a model similar to mine or what I am describing, I could give a picture pinout and you can tell me what color wife is there, since my problem is probably very slight.  Or pictures would help, anything I am desperate!

[animosity^2]

I am the only one in the country with this amp?  I can't seem to find anyone with a working model!

[Anonymous]

Hi,

I will be replacing some caps in mine the coming weeks. I'll take pics of the inside.. my cam doesn't do macro too well, so ill have to test to see if the pictures will be of any help.

[animosity^2]

desperately seeking "Guest" for good times...

*at wit's end*
AAAAAAAAAHHHHHHHHHHHHHHH!!!!!!!!!!!!!!!!!!


Is this amp servicable or am I humping a dead moose here?
Any thoughts?  

[animosity^2]

So, in the months i've been trying to get help on this thing, no one has any clue as to where wires run in this thing?  No one has a functional model i could compare it to?  What good is this forum?

[loudthud]

OK, see if you can follow this. I don't have an amp, just a book of schematics. This is from a schematic that is titled "Concert Bass" with a large "89" outside the title block. I can't read the dates but the last ECN is #353. The circuit board for the power amp is 32-0042 and 32-0040 for the preamp. This is the famous "flying bridge" circuit where ONE of the 2N3055 output transistor's emitter will measure about 0.27 ohms to ground and ONE of the collectors of the other transistors is grounded. The output circuit power supply is floating. I have a schematic for a "Concert Slave" dated 9/26/75 that is completely different.

The driver transistor Q1 (2N3055): base to 10, emitter to 11. Collector goes to brown wire on transformer. Black wire from transformer goes to +32V source which apparently goes to the + side of a 1000uF cap connected to pin 24 of the board.

other transformer connections
White to 4 (base of Q4)
Gray to 9
Yellow to 3 (base of Q3)
Green to 8
Blue to 5 (base if Q5)
Violet to 6
Orange to 2 (base of Q2)
Red to 7

Transistor connections: all emitters go through .27 ohm 10W resistors.
Q2: C-13, B-2, E-12
Q3: C-17, B-3, E-15
Q4: C-17, B-4, E-20
Q5: C-19, B-5, E-22

[animosity^2]

That is, coincidentally, the same schematic I've been trying to work off of, did I am not the best at deciphering schematics (mostly use to follow paths) and did appreciate an english explanation.

A comparison to how my power amp board is wired DID SHOW SOME DESCREPENCIES.  Here is how they compared:

There are 4 wires going to a 810 ohm 2W and a 22 ohm 2W resistor pair each directly from the transformer.  These four are colored as GREY, GREEN, VIOLET, and RED as per the schematics.  However, on my amp, they are colored VIOLET, ORANGE, YELLOW, and GREY.  2 out of 4 right if the colors didn't change from my model to the schematics model.

There are 5 wires, one of each going to a different output transistor, though it's hard to follow to which pin on each.  According to the schematics, they should be colored BROWN, WHITE, YELLOW, BLUE, and ORANGE.  On my amp, they are colored BLUE, BROWN, RED, GREEN, and WHITE.  Of course, these are the transformer wire colors going to the power amp board, there are different colored wires in most cases jumping back off the power amp board to the transistors.

This leaves me in the same boat.  I am not sure if the color code changed at all (doubtful), or if wires were incorrectly hooked back up to the power amp board.  Also, how are the output transistors numbered along the back panel?  If looking from the front, does it start with Q1 at the left and increasing as they go right, or reversed, or out-of-order?

Any help is and will be EXTREMELY appreciated!