GK 250ml amp transistor replacements

[nosaj]

Notice the key letter?

"C"

I just verified they are the c version. Something upwind must be pulling it.

nosaj

[The Dude]

When you fired it up sans limiter, where the speakers hooked up? If so, unhook them next time and check for DC on the output before hooking them up.

[nosaj]

When you fired it up sans limiter, where the speakers hooked up? If so, unhook them next time and check for DC on the output before hooking them up.

Will do gotta see what I have left in stock.
nosaj

[nosaj]

Will do gotta see what I have left in stock.
nosaj

Ok put in tip 35 and tip36s. No limiter Amps moves up to 3.5a not seeing any DC on speaker outputs(speakers disconnected). Thing gets really hot so I shut it down.
Kinda of at a loss on where to go next.

Thanks,
nosaj

[nevetslab]

Notice the key letter?

"C"

Important detail, as the letter suffix on the TIP parts specify the Vceo/Vcbo ratings. Very significant detail when you look at the Safe Operating Area graphs.

[nosaj]

Important detail, as the letter suffix on the TIP parts specify the Vceo/Vcbo ratings. Very significant detail when you look at the Safe Operating Area graphs.

They are the C version that I put in.

They are a 100vDc for the Vceo/Vcbo. so they're equivalent to the tip33/34c called for.

nosaj

Ps. Because the thing is heating up so much and not showing DC on outputs I'm gonna scope the output to see if it's oscillating.

[g1]

They can be idling way too hot and still not have DC on the output. What kind of voltage are you seeing at each of the output devices emitter resistors?

[nosaj]

They can be idling way too hot and still not have DC on the output. What kind of voltage are you seeing at each of the output devices emitter resistors?

q13 2vdc
q17 2.4vdc
q27 3vdc
q31 2.1vdc


q27 and q31 right before I quit they started to register 30vdc on both. Had 2 multimeters hooked up so I could do 2 measurements at a time.

nosaj

[52 Bill]

Like most power amps, you need to measure the voltage across the output emitter resistors with no signal and no load. If I remember correctly, GK lists the correct bias setting as 10mV across the resistors.

Look at the schematics for the bias pot and the bias setting data.

Additionally, you may still have a circuit problem that is causing the output to run hot. Have you checked all of the driver transistors and related resistors?

[nosaj]

Like most power amps, you need to measure the voltage across the output emitter resistors with no signal and no load. If I remember correctly, GK lists the correct bias setting as 10mV across the resistors.

Look at the schematics for the bias pot and the bias setting data.

Additionally, you may still have a circuit problem that is causing the output to run hot. Have you checked all of the driver transistors and related resistors?

I will be on that Sat morning I appreciate the input from everyone.

Thanks,
nosaj

[g1]

q13 2vdc
q17 2.4vdc
q27 3vdc
q31 2.1vdc


q27 and q31 right before I quit they started to register 30vdc on both.

If you had 0VDC at the outputs, and 2 or 3 V at those emitters, you would have 6amps or more through the output devices. (2V across .33 ohms)
Not good. The 30V at the emitters right before you quit was probably the emitter resistors opening up.

[nosaj]

Not sure I read them right, but the outputs are toast again. I went through the schematic for the resistors matched up to the layout.
Some of my readings I took notes to lift a leg tomorrow on some of them to get the true values.
I did not find any burnt or open ones.
But with the outputs out and it fired up something is still pulling current. How might I divide and conquer this? Would cutting a power trace for one of the amps be a feasible way to tell which side is pulling down?

Thanks,
nosaj

[The Dude]

Did you have the speakers disconnected when you fired it up? Most likely the bad side will be outputting DC. That would be my first check.

[nosaj]

Did you have the speakers disconnected when you fired it up? Most likely the bad side will be outputting DC. That would be my first check.

No speakers were not connected. And output transistors are not installed at the moment. But firing it up right now ammeter will run up to almost an amp which to me says something is pulling that shouldn't be. Which is why I asked if I could separate the amps somehow.
Thanks,

nosaj