Results of light bulb current limiter ?

[gtrplayr1976]

Ok...I get that...but if the voltages are different, how would you find a problem ? I mean if you go by the TPs on the schematic, and they don't read correctly. I really like the fact that the limiter allows you to do this, but I guess I'm not experienced enough to figure how to track down the issue.

Thanks for the help ,and Jazz ..I will try disconnecting the speaker also, and checking for voltage.

[stokes]

When troubleshooting a tube amp,you plug the amp into the limiter,the bulb indicates a short,you pull the first power tube,the lamp dims,you have a shorted tube,if the bulb stays bright,you replace that tube and continue pulling tubes one at a time till you get the bulb to dim.If it doesnt when pulling any tube you move on to your power filters and so on.As Jazz P pointed out,it does appear your problem could be in the output,I myself dont work on solid state,I was merely pointing out that the bulbs wattage could give you false readings if not big enough,but if the bulb dims when you disconnect the speaker,you have found at least one issue.

[gtrplayr1976]

Thanks Stokes...That's where I'll start. I've changed a few of the parts on that circuit board...actually most of the major components...I'll get a 100 watt bulb,and go through it again.

[52 Bill]

For now don't worry about the wattage of the bulb. Do as Jazz P Bass suggested and read the voltage on the output with no speaker attached.

When the amp is in fault mode, the power supply will not get up to normal levels. The light bulb will cause a drop in voltage that will save your new fuse and new parts. That's the point of using the light bulb, to limit the current draw of the amp if there is still a problem with the circuitry.

You need to continue troubleshooting the amp circuit.

[gtrplayr1976]

Thanks Bill... I'm taking a look at that first chance I get. probably tomorrow since I have a 16 hr work day today...

[Jazz P Bass]

O/k.
It's a Crate 165B amp rated at 60 watts output.
At idle I would assume a working amp draws around 15 watts from the AC mains.
Class A/B.
At full power it "might" draw 120 watts.
I would remove the output transistors & the drivers & diode check them on the bench.
Something is pulling way too much current.
It sounds like the problem is in the output section.
You had a dimmly glowing lamp without the speaker connected.
Then it went bright with the load connected.

[gtrplayr1976]

O/k.
It's a Crate 165B amp rated at 60 watts output.
At idle I would assume a working amp draws around 15 watts from the AC mains.
Class A/B.
At full power it "might" draw 120 watts.
I would remove the output transistors & the drivers & diode check them on the bench.
Something is pulling way too much current.
It sounds like the problem is in the output section.
You had a dimly glowing lamp without the speaker connected.
Then it went bright with the load connected.

Ok...would that be Q7, Q8, Q9,Q10 ? Diode check?

Thanks Jazz

[Jazz P Bass]

Do you have a schematic that you could post.
I do not know Q7-Q10 from Adam.
Diode check is a function of a Digital Multi Meter.
It allows you to check the junctions of diodes & bipolar junction transistors.

[gtrplayr1976]

Do you have a schematic that you could post.
I do not know Q7-Q10 from Adam.
Diode check is a function of a Digital Multi Meter.
It allows you to check the junctions of diodes & bipolar junction transistors.

Hoepfully this will work...

[Jazz P Bass]

Q7 is the driver for Q9 output transistor. NPN stage
Q8 is the driver for Q10 output transistor. PNP stage.

The input signal enters the differential pair, Q1/Q2.
Q1 drives Q3.
Q4( Edit) is the bias transistor.
Q3 drives Q7/Q8 & they drive the output transistors Q9/Q10.
Q5/Q6 (edit ) are protection transistors. When turned on they rob driver current.

[gtrplayr1976]

Q7 is the driver for Q9 output transistor. NPN stage
Q8 is the driver for Q10 output transistor. PNP stage.

The input signal enters the differential pair, Q1/Q2.
Q1 drives Q3.
Q7 is the bias transistor.
Q3 drives Q7/Q8 & they drive the output transistors Q9/Q10.
Q4/Q5 are protection transistors. When turned on they rob driver current.

What does Q6 do?

[Albert Kreuzer]

Some numbers in the schematic are barely readable.
Q4 is the bias transistor.
Q5/Q6 are the protection transistors.

[gtrplayr1976]

Some numbers in the schematic are barely readable.
Q4 is the bias transistor.
Q5/Q6 are the protection transistors.

Thanks for the info. I think it looks a little clearer if you save the picture , and expand it .

[gtrplayr1976]

Q7 is the driver for Q9 output transistor. NPN stage
Q8 is the driver for Q10 output transistor. PNP stage.

The input signal enters the differential pair, Q1/Q2.
Q1 drives Q3.
Q4( Edit) is the bias transistor.
Q3 drives Q7/Q8 & they drive the output transistors Q9/Q10.
Q5/Q6 (edit ) are protection transistors. When turned on they rob driver current.

Thanks Jazz

[gtrplayr1976]

Well..I guess there is obviously an issue...I checked the voltage on the speaker out with speaker disconnected....28VDC...geez