Hello, everyone , i'm repairing a YBA built-in Delta DT I already changed all the power transistors (TIP35 & TIP36) and also change the 2 transistors for bias adjustment (reference BC547?) Plus Two adjustable resistors for the bias, the amplifier turns on properly, but I can not adjust the bias, with a multimeter, the values do not move! I do not know if the 2 transistors bc547 are the right reference for this amp? Because the manufacturer has erased all the references of its parts on its components, does anybody could provide me the references of the parts of the transistors for the bias and also to what value it must be adjusted? 1.6millivolts ?? thank you.
Attachments
Hello sisko84,
I used to repair YBA equipment, and still occasionally do, and the transistor used for bias was BC651CS.
Make sure the pins are not reversed because I think that for the BC651 it is ebc and for the BC547 it cbe.
Make sure the output transistors are soldered correctly to both side of the pcb as it is a double sided pcb but without through hole plating. The same comment goes for the bias trimmer I see you replaced.
Bias should be adjusted so you measure no more than 2 mV (±0.2 mV) on any emitter resistor.
You should have that same 2 mv on all 8 emitter resistors.
If not, it means your output transistors are not matched.
If you have no way to match them, at least make sure the PNP output transistors are from the same batch number, the same goes for the NPN.
If you need any parts, I pretty much have everything in stock to fix any YBA equipment made prior to 2010.
Let me know how it went.
Regards,
Michel
I used to repair YBA equipment, and still occasionally do, and the transistor used for bias was BC651CS.
Make sure the pins are not reversed because I think that for the BC651 it is ebc and for the BC547 it cbe.
Make sure the output transistors are soldered correctly to both side of the pcb as it is a double sided pcb but without through hole plating. The same comment goes for the bias trimmer I see you replaced.
Bias should be adjusted so you measure no more than 2 mV (±0.2 mV) on any emitter resistor.
You should have that same 2 mv on all 8 emitter resistors.
If not, it means your output transistors are not matched.
If you have no way to match them, at least make sure the PNP output transistors are from the same batch number, the same goes for the NPN.
If you need any parts, I pretty much have everything in stock to fix any YBA equipment made prior to 2010.
Let me know how it went.
Regards,
Michel
Hi. I have some questions. I hope help me, thanks.
I have 8 transistors, 4 each channel. I don't know which are first two, secont two..,, etc.
Are the PNP, PNP, NPN, NPN and PNP, PNP, NPN, NPN or no?
How to solder BC 651? With ''face'' to radiator or with ''back'' to radiator.
Last question. Where to put multimeter +/- to set mv? Between which elements?
I have 8 transistors, 4 each channel. I don't know which are first two, secont two..,, etc.
Are the PNP, PNP, NPN, NPN and PNP, PNP, NPN, NPN or no?
How to solder BC 651? With ''face'' to radiator or with ''back'' to radiator.
Last question. Where to put multimeter +/- to set mv? Between which elements?
Dear Michel,
I know that you are a great expert of YBA amplifiers.
If possible, I kindly ask you how much should be the BIAS value for the old YBA 1HC Alpha power amp.
I measured 0.20 Ohm of emitter resistance. The amp now has BIAS=1.5mV (less than 8mA), but that seems
quite low to me. Do you have any suggestion, a part taking my -very long- time to set the BIAS of this amp...?
Trying higher BIAS (e.g. 4mV) THD at high frequency decrease a lot (eg 12dB at 20kHz, mainly because of
second harmonic).
Many thanks in advance!
Tino
P.S. It seems I don't know anymore how to send personal messages... sorry!
I know that you are a great expert of YBA amplifiers.
If possible, I kindly ask you how much should be the BIAS value for the old YBA 1HC Alpha power amp.
I measured 0.20 Ohm of emitter resistance. The amp now has BIAS=1.5mV (less than 8mA), but that seems
quite low to me. Do you have any suggestion, a part taking my -very long- time to set the BIAS of this amp...?
Trying higher BIAS (e.g. 4mV) THD at high frequency decrease a lot (eg 12dB at 20kHz, mainly because of
second harmonic).
Many thanks in advance!
Tino
P.S. It seems I don't know anymore how to send personal messages... sorry!