a few years ago my friend built me this hybrid amp,now he move to other country and i lost contact with him.
this amp now damage,it has distort sound,such like clipping on every volume.
after i turn off the amp,i measure the dc offset on one channel,it show -50vdc,after the relay click on.
somebody can help me please..
here is the schematic for input stage (tube) & output stage
lot of thanks for the help
this amp now damage,it has distort sound,such like clipping on every volume.
after i turn off the amp,i measure the dc offset on one channel,it show -50vdc,after the relay click on.
somebody can help me please..
here is the schematic for input stage (tube) & output stage
lot of thanks for the help
Attachments
transistors information:
q42= a970
q58= c2240
q43= d669
q57= b649
q44= 2n6488 (not mje 3055)
q56= 2n6491 (not mje 2955)
q45= c3281 ,4 pcs each channel
q52= a1302 ,4 pcs each channel
the emitter resistor for q45 and q52 are 0.47ohm,they are not bypass such on pic
the supply are +/- 55vdc
q42= a970
q58= c2240
q43= d669
q57= b649
q44= 2n6488 (not mje 3055)
q56= 2n6491 (not mje 2955)
q45= c3281 ,4 pcs each channel
q52= a1302 ,4 pcs each channel
the emitter resistor for q45 and q52 are 0.47ohm,they are not bypass such on pic
the supply are +/- 55vdc
Member
Joined 2002
q45= c3281 ,4 pcs each channel
q52= a1302 ,4 pcs each channel, toshiba's 😀
So are you saying there is 55V on the speaker output ?
yes, -50,... vdc on the speaker output ,when the relay turn on,but when the relay still turn off,there is no significant dc on output speaker,and that just on one channel,other channel is normal,but the sound is distort,like clipping.
thanks
thanks
.
You verify before the fuse on negative and positive rail. If it is Ok, then it miss the bias in the upper half. If fuse is broken, then you have a transistors short circuit in the relative side.
Francesco.
Just quickly looked at this.
If it only gives DC offset when relay closes it must be that 0.22mfd cap on the valve output.
If it only gives DC offset when relay closes it must be that 0.22mfd cap on the valve output.
thank you,all transistors were check and they are normal,the fuse also ok,and i don't know where to set the bias for that amp,there is no bias pot as you see on schematic
cheers
Yes, i not be seen your answer before: if you have dc offset only with relay on, then you have the 0,22 cap in short.
Francesco.
thank you very much,i was ever try to swap the cap 0,22uf for left channel and right channel,but the problem is still on same channel,the tubes was swap also for left and right,the result is the same
uuufffhhh... very headache
Are you saying you have swapped the cap and it's still faulty ?
If you only get an offset when the relay at the output of the valve closes then either the cap must be leaky or there is some strange wiring fault/short etc.
It's not possible for it to be anything else.
Remove the cap and see if the offset problem remains when the relay closes.
Extremely obscure is the posibility that the valve stage is oscillating, you would need a scope to check... or remove the valve.
If you only get an offset when the relay at the output of the valve closes then either the cap must be leaky or there is some strange wiring fault/short etc.
It's not possible for it to be anything else.
Remove the cap and see if the offset problem remains when the relay closes.
Extremely obscure is the posibility that the valve stage is oscillating, you would need a scope to check... or remove the valve.
is it something wrong with the circuit?,maybe anyone have an idea for modify it?,add capacitor for prevent oscillation?,add feedback?,or change driver stage?etc,etc..
thanks
thanks
Tomat,
Another thought. Is the circuit correct ?
Is the relay really where you have drawn it, or is it at the speaker output which would be more "normal" ?
Another thought. Is the circuit correct ?
Is the relay really where you have drawn it, or is it at the speaker output which would be more "normal" ?
thank you ,yes i swapped the cap and the problem still there,when relay is not connect with the valve stage (relay shorted to ground),there is no dc offset on output
yes,the circuit is correct,and the relay is true on there,between valve stage and amp stage
thanks
Try removing the cap then.
If you have put 50 volts across the speaker that may well not have survived.
If you have put 50 volts across the speaker that may well not have survived.
very sorry,i forget something on circuit,there is caps 47pf on collector to base q42 and q58, if i remove those caps the 50vdc is gone,but this happen only in one channel,the other channel still fine altough the caps still on there.
and the other problem,the sound is very distort on both channel,very weak,such like clip on every volume
thank you
and the other problem,the sound is very distort on both channel,very weak,such like clip on every volume
thank you
Hi Tomat,
You need to step back and start again 🙂
The relay is drawn incorrectly... you mention it shorting the input to ground... yes !
If so it's possible there is a problem in the power amp and the effect of shorting the input is masking the problem... particularly with you saying removing 47pf caps stops problem.
You need to isolate the where the fault lies, power amp or valve stage/relay.
You need to step back and start again 🙂
The relay is drawn incorrectly... you mention it shorting the input to ground... yes !
If so it's possible there is a problem in the power amp and the effect of shorting the input is masking the problem... particularly with you saying removing 47pf caps stops problem.
You need to isolate the where the fault lies, power amp or valve stage/relay.
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