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Old 14th January 2008, 08:34 AM   #2021
Harry3 is offline Harry3  Australia
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Hi Bob,
you can cross my name off your list. I have recieve the diodes and boards from Mark.
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Harry
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Old 14th January 2008, 12:20 PM   #2022
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Quote:
Originally posted by TWS
Hehe, i can add another 70 kg to the collection if thats whats needed
And dont forget to add 70 to 80 kgs of big transformers too.....

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Old 14th January 2008, 12:54 PM   #2023
TWS is offline TWS  Denmark
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Default Grrrrr

Yeah i know these things get heavery, my stereo version weighs in at 80 kg, that more than myself lol.
But now to a different matter, to get a little "in shape" for this build i wanted to give my old mono's a overhaul, and i discovered this: When i power up amp 1, it initially pulls around 3 amps from mains, then it slowly sinks to around 2 amps and then stabilize at 1,8 (at 230 vac of course)
Amp 2 is quite different, it pulls 5 amps when turned on, and then slowly stabilizes around 1,8 too after app 30 mins.
I was measuring here and there, but i cannot find a reason for this difference, my worry is the surface temp of the 15024/25, it gets really high when around 1150 watts are running thrugh them during warmup. The bios trans if of course mounted with the drivers, so no help there.
As i said, i was measuring different things, all voltages seems to be identical im both, so im a little confused. My Q is, exactly what is responsible for the current draw when everything is cold ? I tried to take out the bios trans and mount it directly on top of one 15024, that helped ofcourse a lot, but i dont see why this is a problem with only one of the amps.....Anyone ?
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Old 14th January 2008, 01:00 PM   #2024
AndrewT is offline AndrewT  Scotland
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hi,
different ballast resistor/thermistor in the primary.
different ballast resistor/thermistor in the cap charge circuit.
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Old 14th January 2008, 01:37 PM   #2025
TWS is offline TWS  Denmark
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Thank you for the suggestion, and i wish that was the case, but the power trans in amp 2 gets much hotter than in amp 1 during "boot" im a little scared........
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Old 14th January 2008, 04:31 PM   #2026
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Power amps

has significant different bias current when cold at start up. After bias has settled in about 30 min the bias current is approx the same for both amps, right.

Could be a problem with the drivers due to aging and transistors ages by time with temperatures, especially if running hot for many years. Hfe could have change, also older electrolytic capacitors when running in hot environment, could have higher leaking currents etc..

Check especially the big power electrolytics, one or both could be faulty and they could have high leaking currents when powering up. Check for temperature rise after powering up that amp. If no change in temperature, they are probably fine.

Try measuring the bias voltage over the outputs emitter resistors (should be the same on both amps) and it should read approx. 0.625 V but is dependent on the quantity of outputs in use and chosen value for these resistors.

My two cents

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Old 14th January 2008, 05:03 PM   #2027
TWS is offline TWS  Denmark
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Thank you for your 2 cents, i think you are on to something.....
To make a long story short, i swapped the pcb's in the amplifiers, and the error followed the board. I guess my caps are in the clear then. When i measure the emitters during startup, of course they are different, amp 2 is getting around 50 % more current during startup, after warmup they are identical. I guess its time to change "suspicious" parts, already did the zeners and current regulators, no change. Any ideas about where to begin ? If i change the bios transistor to one with a higher hfe, it helps a bit but still far from the same. Its scary to see my vario max out a 5 amps and stay there for 15 minutes !
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Old 14th January 2008, 05:22 PM   #2028
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I was just going to post a tip for you: swap the two driver main boards, but you have already done that,

Yes, it seems to be some problem with one of the two boards. Try to measure the drivers for good hfe and check for second brake down, could be a small leaking current in one or more of the drivers (Q9-Q12 + Q13). Also compare the readings to a new transistor of the same type. Also check for the 39V (the zeners in LTP) is ok?

Oh, yes the power electrolytics are probably fine.

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Old 15th January 2008, 05:28 AM   #2029
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Great to see Mark is OK and all of the stuff is being sorted out. I'm looking forward to this thread coming to life again.

Blessings, Terry
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Old 15th January 2008, 12:46 PM   #2030
TWS is offline TWS  Denmark
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@ Flodstroem
Finally managed to get it running again within my current tolerance, i simply replaced every active component on the board
I think it was the drivers that was responsible, when the amps were build, they were matched pretty exact, and now they are off by 20 % easy ! Another thing was, i found an emitter resistor to be unstable, they are 0,2 ohms 1% caddoc types. I think i overtightned it when it was build, they really dont like that.
I guess living in 50 celcius for 10 years dosent do them any good at all.....maybe i should start to turn them off when not in use....
Anyway, thank you all for your input and suggestions, its highly appreciated !

Greetings

TWS
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