help this mikawa amplifier, cheap but weird

[Mooly]

I am give up...
Sorry i can not do it like what you said before...
I am so sorry...

I have plan for use their origin value of passive components

But i have small plan like my 2N3055/MJE2955
I put a resistor after Q5 to Q6...
It was 150 ohm...
But one question
Is R7 33K contributing give hum

That's all right A fixed bias amplifier like this is critically dependent on the exact semiconductors that were used in the initial design. Change those and the bias could be way off.

R7 !

Well amplifiers in themselves don't hum. The hum comes from elsewhere, perhaps the power supply, perhaps poor electrical layout, there could be induced hum from the transformer etc.

R7 sets the gain of the amplifier. The higher the gain, the more noticeable hum problems might be however altering the value of R7 isn't good because that could alter the stability of the amplifier and make it prone to high frequency oscillation.

 

[fandi bin stress]

That's all right A fixed bias amplifier like this is critically dependent on the exact semiconductors that were used in the initial design. Change those and the bias could be way off.

R7 !

Well amplifiers in themselves don't hum. The hum comes from elsewhere, perhaps the power supply, perhaps poor electrical layout, there could be induced hum from the transformer etc.

R7 sets the gain of the amplifier. The higher the gain, the more noticeable hum problems might be however altering the value of R7 isn't good because that could alter the stability of the amplifier and make it prone to high frequency oscillation.

i have 20K resistor stocks, can i use them???

cause i have no idea for buying more another parts...

you are right about the stability of the amplifier...

my TIP42C is hotter than TIP41C only about 10 seconds after turning on(after put a 150ohm resistor)...

and feel something like shaking in heat heat sink...

that was so strange...

 

[fandi bin stress]

That's all right A fixed bias amplifier like this is critically dependent on the exact semiconductors that were used in the initial design. Change those and the bias could be way off.

R7 !

Well amplifiers in themselves don't hum. The hum comes from elsewhere, perhaps the power supply, perhaps poor electrical layout, there could be induced hum from the transformer etc.

Can i take my words --- >>> I AM GIVE UP ???
I have been found some troubles in this circuit...
Now i.will solving it...
Thanks boss
You are great

 

[de Ocampo]

 

[fandi bin stress]

That's all right A fixed bias amplifier like this is critically dependent on the exact semiconductors that were used in the initial design. Change those and the bias could be way off.

R7 !

Well amplifiers in themselves don't hum. The hum comes from elsewhere, perhaps the power supply, perhaps poor electrical layout, there could be induced hum from the transformer etc.

R7 sets the gain of the amplifier. The higher the gain, the more noticeable hum problems might be however altering the value of R7 isn't good because that could alter the stability of the amplifier and make it prone to high frequency oscillation.

Update :

After some experiments, some searchings...
Amplifier circuit is ok and no hum again after give it the original value components and add a 150 ohm resistor before Q6

Other problems just rising...
TC tone control somehow nothing short by eyes sighting and measuring
But it produces bad sound and one channel dead
Well, changing some caps(the origin has bad value) and some transistors(the origin is bad)
But still dead one

So i have an idea
I have old tone control and same topology, 2 transistors each channel
But i need to add more cables for fixing variabel resistors position...

Wish it will solving my problem

Regards

 

[Mooly]

It sounds like you are having fun and learning

A faulty tone control should be fixable if measure the DC conditions and then trace the signal through from input to output.

 

[fandi bin stress]

It sounds like you are having fun and learning

A faulty tone control should be fixable if measure the DC conditions and then trace the signal through from input to output.

"it sounds like you are having fun....."

those words uggghhhh...

my head almost being some pieces dude

this amplifier have many faults...

but if i didn't save amplifier section from first time(testing sounds using my tone control and my active cross over at mid section = great no problem)...

it will gives me more headache...

well, DC conditions is okay but the tone control itself...

i don't know what's wrong or not but changing the tone control section is better idea...

you know, i am so tired at amplifier section before

next post, i will show you what i've done

 

[fandi bin stress]

A faulty tone control should be fixable if measure the DC conditions and then trace the signal through from input to output.

Yups...
I have been realized this amplifier has 5 problems...
1. Amplifier section, weird schematic, dead channel, hoarse sound
2. Amplifier power supply section, crack on the solder area, caps looks like too old
3. Tone control power supply, dead of power transistor supply 12VDC(change it from s9014 to 9013)
4. Variabel resistor for volume control, change the old to new one, bad solder manufacturer
5. Tone control(this is the last thing i've touched), dead one channel, solder crack, bad pcb

So far this amplifier was alive again...
1 and an half week confused for this one...
After finishing problem no 1 to 4, i think it's done but not...

Thanks for your help Mooly...
Once again you are great...

 

[fandi bin stress]

#update

Final touch for reposition cable, reposition variabel resistor, securing cable join, making new base for its new parts and re-soldering all of the section cause this amplifier is an old product, it was 18 years ago...

Those TIP41C/TIP42C only get warm not hot or fever using its original transistor...

 

[de Ocampo]

...and you are doing this all for free, you should be given a medal

 

[fandi bin stress]

...and you are doing this all for free, you should be given a medal

not free at all...
you know...
my relative(usually) will give me some money, not big not much but just some money as "thank-you note"...
they will said "just some money for buying cigarettes"...


but for some parts which is broken, i said they should pay it cause there is an agreement "reimbursement of the purchase of spare parts"...

 

[fandi bin stress]

FINALLY... yep!!! finished...

well, after fighting with this amplifier for some days...
after some helps from great buddies here...

FINALLY...

FINISHED!!!

sounds so good, no hum, final transistors only warm after 2 hours playback music at 50% volume...

my last jobs is last finishing...

Thanks everyone...

note : first picture is important parts for amplifier section, second picture is last sight before final touch and during testing only

 

[Mooly]

Well done So it was a solder crack stopping the tone section working.

And when you look back you will see that you were having fun

 

[fandi bin stress]

Well done So it was a solder crack stopping the tone section working.

And when you look back you will see that you were having fun

actually for tone control section it was not crack

after searching for some many times i am still can't figure out what's wrong even with many times measuring(next time i will take it to my friend place using his microscope)

so i change tone control section with my old(my old experimental, long time not use about 6 years)

just ex-change some their discrete components

but re-soldering is not an option for normal repairing but i choose re-soldering for another section and completely done

well, personally without you i can't solving this one

thank you very much buddy...

you are great

 

[fandi bin stress]

this is before and after ex-change tone control section

 

[Mooly]

You're very welcome I'm just pleased it all worked out OK for you in the end.

 

[fandi bin stress]

You're very welcome I'm just pleased it all worked out OK for you in the end.

And we will help others too...