Simplest way to bias a power transistor || SANSUI A-7 amplifier
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- čas přidán 24. 11. 2022
- Simple way of biasing a output transistor of an amplifier. This is my way of biasing a solid state amp especially if I don't have the exact bias voltage no schematics or service manual. If any of you knows the exact bias voltage for this amp. please comment below and thank you in advance.
Thank you for this very informative video
Glad it was helpful! Welcome
We’ll explain. Thanks for advice
You're welcome
Thank you for this video. I just recently bought an a-7 and wondered if you can help me about the power switch, it has static sound when switching on and off the power. Thanks
Welcome... Try to replace the capacitor in the switch and clean the power switch.
not all vintage stereo had has the same biasing voltage.
There are .11 or .8 .7 and something.
The factory biasing settings of sansui a-7 is .7mv
But in my field of repair the sansui is not sensitive in lowering the biasing voltage not like the vintage pioneer stereo amplifier
The sansui integrated can be converted the trim bias into fix resistors. And if you were curious try to use 1k resistors or 1.2k series connection to replace the trim.
Thanks for the info.
From your measurements, what is then the Collector and Emitter Currents?, because from these you would know the power dissipation of each transistor and if your transistors are within the safe operating area (SOA), the SOA of transistors can be found from its specifications.
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That is good, can that be applied to any other similar amplifier, both VBE ~~ .500 Volts ?
Yes it is the safe way 0.5V bias actually this is cold bias. I don't have the schematic diagram of this unit and If ever you have the correct bias of your unit that's the best bias if in case you don't have then go for a cold bias. Or you can crack this up but do it little by little just observe the heat dissipation of your power transistors.
I've got a Pyle pt1200 amplifier that uses a pair of transistors 2sc5200 and 2sa1943 and has a small transistor in the middle of them (3421) on ch 1 and ch 2 and has 1 trim pot 100 k per channel can I use the same method you used connect my red probe to the base and black probe on the (e) of the pair and adjust the pot , Can I just do the adjustment on one of the 2 transistors in each channel ?
Each channel has only one biasing trimmer you need to get the nearest average bias voltage of the two transistor in each channel. Example if you set the one transistor at 0.5V the reading of the other transistor might be 0.49V or 0.52V in the real world you can't get the same voltage on both transistors just get the average of the two.
I switched my amplifier on and after a minute I tried adjusting the pot on channel 1 (red probe on base and black probe on the emmiter of the output transistors )it shows 0.500 on ch 1 and when I tried on ch 2 it reads 0.464 if I turn up or down the reading stays the same must I disconnect the fan cooling the sink ? It's my first time biasing a class ab amplifier any help will be greatly appreciated.
The 0.46 one channel and the other is 0.5 that's fine. Try to adjust the 0.5 back to 0.464 to have the same bias with the other channel. The 0.46 is just fine.