Ampeg B200R Bass Amp

[Jazz P Bass]

How much current is flowing through each 0.33/10 watt resistor.

[J M Fahey]

Also there appears to be 4.5 volts ac on speaker measured one way reverse leads read. 1 volts on meter A/C range not sure if this. Is really A/C or not

No, it's DC .

But cheap multimeters get confused measuring DC, they think it's roughly 2.5X higher AC.

The telltale sign is that it measures 4.5V one way , 0.1V the other ... AC would be symmetrical so you actually have some 2V DC there .
Confirm by remeasuring on a DC scale, also measure both rail voltages.

Your amp will eat lots of current, even if using all new parts, if overbiased, but first answer the previous questions, then we go on.

[robgrif]

There is 49.5 milivolts through them I tried to adjust it down but it did not go lower the bias pot measures 500 ohmns and responds to adjustment down to zero.

[robgrif]

20.7 @source q8 20.8 source @q11

[robgrif]

Sorry wrong meter scale. Reading is 49.5 milivolts dc . On. 33 ohmns resistors

[robgrif]

ok replaced power supply caps one was causing more current to flow when touched.still drawing excess current. would it be possible for U3 to be causing this problem.?just guessing now.

[Jazz P Bass]

How about taking a few static (no signal) voltage measurements.
The drivers & the bias transistor.(EBC)
U3 output pin should sit at zero volts.

[robgrif]

How about taking a few static (no signal) voltage measurements.
The drivers & the bias transistor.(EBC)
U3 output pin should sit at zero volts.

ok thanks here are the values that I got
Q7 E=+.06 v C=+18v B=+3.16v
Q6 E=-.06 v C=-18v B=-2.6v
Q3=E 2.6v C=3.16v B=1.5 v
U3 ouput = 0v
light bulb limiter 60 watt bulb

[The Dude]

It would appear from your measurements that Q6 and Q7 are open. Also check R41, R43, R58, and R67.

[robgrif]

[QUOTE=The Dude;367281]It would appear from your measurements that Q6 and Q7 are open. Also check R41, R43, R58, and R67.[
ok checked those resistors all good

[robgrif]

It would appear from your measurements that Q6 and Q7 are open. Also check R41, R43, R58, and R67.

thanks
checked the resistors they are all correct values and good
as for q6 and q7 not sure what is happening there.

[The Dude]

If the voltage is the correct polarity from b to e on a transistor, the only way it can be more than .7 or so volts on a standard transistor is if the transistor is open/bad/defective.

[Jazz P Bass]

I am not too sure that this applies to the circuit.
The emitters are opposite polarity, so they blend to the voltages shown.

I would question why, with a 60 watt limiter, the 50 volt rails are sitting at 18 volts.

It may be time to ditch the limiter, as it may be upsetting the apple cart.

I would install a 1 amp fuse in the mains fuse holder & have at it.

[robgrif]

I am not too sure that this applies to the circuit.
The emitters are opposite polarity, so they blend to the voltages shown.

I would question why, with a 60 watt limiter, the 50 volt rails are sitting at 18 volts.

It may be time to ditch the limiter, as it may be upsetting the apple cart.

I would install a 1 amp fuse in the mains fuse holder & have at it.

ok thanks something strange is happening.when the emitter of q7 is touched with + probe from meter light limiter dims amp starts to hum and dc on speaker goes to -47 volts. i have two meters this behaviour only happens with one of the meters and does not require other test lead to be hooked to anything . why would this happen? is meter acting as some sort of capacitor or ???
shall i go for fuse install anyway

[robgrif]

I am not too sure that this applies to the circuit.
The emitters are opposite polarity, so they blend to the voltages shown.

I would question why, with a 60 watt limiter, the 50 volt rails are sitting at 18 volts.

It may be time to ditch the limiter, as it may be upsetting the apple cart.

I would install a 1 amp fuse in the mains fuse holder & have at it.

ok installed fuse it blew also both mosfets q5 and q8 blew as well oops fuse was 2amp my bad
any way this is the same problem originally so whatever it is remains a mystery i will purchase two new mosfets and install