700/1 “Tim” WOPL driver board

[mlucitt]

Dude, the Aerosmith B's would take a chassis and a faceplate...they are ROUGH!!

Lee is a oilfield Roughneck. When he says something is rough, it IS rough.

 

[laatsch55]

True dat...

 

[AngrySailor]

High temp cut out works,,,

 

[AngrySailor]

Put an “ice cube” on the wound...

 

[mlucitt]

High temp cut out works,,,

You have to be careful when the temperature drops enough for the switch to close. Better turn your speakers down...
Ask me how I know?

 

[AngrySailor]

Hmmm fired Tim up today and the right channel getting hot. Pops borrowed my multimeter so I shut things down waiting for him to stop in I’ll check the bias... sounded great, just hot. I’ve pushed it pretty hard at times though too. Also, and I don’t have the schematics or the amp in front of me rn, but I’d like to make the meters more sensitive. They don’t hardly move until you’re really driving the amp hard near clipping. It’s just a resistor value change if I remember right no?

 

[Gepetto]

Hmmm fired Tim up today and the right channel getting hot. Pops borrowed my multimeter so I shut things down waiting for him to stop in I’ll check the bias... sounded great, just hot. I’ve pushed it pretty hard at times though too. Also, and I don’t have the schematics or the amp in front of me rn, but I’d like to make the meters more sensitive. They don’t hardly move until you’re really driving the amp hard near clipping. It’s just a resistor value change if I remember right no?

Turn your bias pots full CCW (all the way down) until you can retrieve your meter to measure it.

 

[AngrySailor]

Turn your bias pots full CCW (all the way down) until you can retrieve your meter to measure it.

Amp is off till then. Refresh my memory, bias is checked from the test point on the board to the emmiter at the DCP right?

 

[MarkWComer]

Amp is off till then. Refresh my memory, bias is checked from the test point on the board to the emmiter at the DCP right?

There are also two testpoints on the backplanes for bias+ and bias - in addition to the one on the driver board, which is positive. If you use the TPs on the backplanes, you should get the same values but opposite polarity.

It’s measured against the speaker/meter outputs OR the “output” TP on the backplane.

Given that there are bias +/- on the backplanes, does this mean that the NPN/PNP banks could “mis- bias” due to an emitter resistor or transistor fault independently and cause a thermal runaway in one column only?

 

[Gepetto]

Amp is off till then. Refresh my memory, bias is checked from the test point on the board to the emmiter at the DCP right?

If your output offset is zero, then you can check from the bias test point on the board to the ground terminal anywhere in the amp.

 

[Gepetto]

There are also two testpoints on the backplanes for bias+ and bias - in addition to the one on the driver board, which is positive. If you use the TPs on the backplanes, you should get the same values but opposite polarity.

It’s measured against the speaker/meter outputs OR the “output” TP on the backplane.

Given that there are bias +/- on the backplanes, does this mean that the NPN/PNP banks could “mis- bias” due to an emitter resistor or transistor fault independently and cause a thermal runaway in one column only?

It means that I put them on there so the inquisitive folks on this forum could check the top to bottom symmetry on their full comp amps

 

[Skratch]

On rev A board its between terminal 6 and 10

 

[AngrySailor]

Bias 350mV left, 580mV right with the pot full CCW. rises to 680mV full CW. DC offset 0v

 

[Gepetto]

Bias 350mV left, 580mV right with the pot full CCW. rises to 680mV full CW. DC offset 0v

What do you have on the back wall at this point?

 

[Gepetto]

Bias 350mV left, 580mV right with the pot full CCW. rises to 680mV full CW. DC offset 0v

And what is the left channel with the pot full CCW (minimum)?

 

[AngrySailor]

And what is the left channel with the pot full CCW (minimum)?

250mV full CCW

 

[AngrySailor]

Amp is cold

 

[Gepetto]

250mV full CCW

That is a good reading for full CCW

 

[AngrySailor]

What do you have on the back wall at this point?

didn’t see this post. All outputs and drivers in. Outputs are 2sd555’s.

 

[Gepetto]

didn’t see this post. All outputs and drivers in. Outputs are 2sd555’s.

What are the drivers in the bottom row?