Overheating 100 ohms?

Sounds like the emitter resistor for the first transistor of a compound output transistor. The second transistor emitter resistor will be 0.5 to 3 ohms. Is it also overheating?

there will be two such transistor pairs per channel

This is a really interesting amp, brings back old memories.

 

Overheating 100 ohms?

Sounds like the emitter resistor for the first transistor of a compound output transistor. The second transistor emitter resistor will be 0.5 to 3 ohms. Is it also overheating?

there will be two such transistor pairs per channel

This is a really interesting amp, brings back old memories.

Thank you for your quote .
I will check & update .

Regarding the amp , yes it is an interesting one ,Also kind of an adventure to work on this amp. To be honest , this is the first time i ever opened up a amp such old & also it being a soviet machine.
Actually i am quiet amazed to see how good was soviet technology during early 80s.

Regarding your quote earlier about my collection of Amps, I have recently started taking interest in Amp collections , To date i have a collection of 3 amplifiers .

Technics SA-EH 7
Yamaha AS-700
Romantika Y-120 (this is the one i am currently working on)

 

I advised you to NOT change the transistors, only resistors and capacitors.

You ignored my advice and have changed the transistors anyway.

Since you changed the transistors, you have had one disaster after another.

Use the voltage readings at the various circuit points that I told you to take when everything was working well, to determine what areas the voltage is different now that it is not.

If you did not take the voltage samples that I DID advise you to do, and changed the transistors which I cautioned against doing, why would I waste any more of my time suggesting things for you to try when you probably won't listen to me anyway?

Good luck fixing it.

 

Something the 100 ohm resistor feeds current to is bad, causing too much current. You need to trace the wiring to see what part of the amp is involved. Do you have a meter to investigate voltage readings in the two channels?

Yes, I do have a meter, once i check them, i will update.
I am just worried about one thing , if the fault is in any of the small transistors, then i fear i wont be able to replace them, transistors are so old that the part number in almost every transistors are invisible.

 

I advised you to NOT change the transistors, only resistors and capacitors.

You ignored my advice and have changed the transistors anyway.

Since you changed the transistors, you have had one disaster after another.

Use the voltage readings at the various circuit points that I told you to take when everything was working well, to determine what areas the voltage is different now that it is not.

If you did not take the voltage samples that I DID advise you to do, and changed the transistors which I cautioned against doing, why would I waste any more of my time suggesting things for you to try when you probably won't listen to me anyway?

Good luck fixing it.

I would deeply like to apologies, but i really think there has been a misunderstanding .

Yesterday in my post , i brought to notice that, due to my lack of knowledge & carelessness , i wanted to renew the thermal paste (as they had Dried up) , once done , i did not use the insulator pads & blew the transistors (Damn i shouldn't have touched them) , now i really regret of what i did.
Since i blew them , i had to change the transistors.

Plz don't think i ignored your advise.

Secondly i do have the Voltage readings as per your advise.

Thirdly , why is it that the right channel is working absolutely fine with the new transistors installed ?

 

Transistors are all different. Even in the same batch, they will have variations.

Something has changed. You have one side that is working, and one side that is not working.

Fortunately for you, the two circuits were probably made identically. So, figure out what is different in the circuit that is not working from the circuit that is working.

 

if the fault is in any of the small transistors, then i fear i wont be able to replace them, transistors are so old that the part number in almost every transistors are invisible.

If you do not have a circuit diagram, it would be possible to fairly easily make one at least with the removable boards. Try shining a powerful light through to see both the track and component side together.

As regards the transistors a list would be very useful just number them tr1,tr2 etc if you can't find their type nos. Whilst the amp is working record the voltages at all three terminals. This will help identify if the transistor is NPN or PNP. I doubt vey much the Soviets went in for speciality transistors so it should be possible to determine equivalents against any replacement.

Back along Mullard (who were copied extensively) published a series of power amp designs with a small signal PNP input transistor whose emitter was coupled to the zero rail via a low value (47 - 100 ohms) resistor through an electrolytic capacitor from the centre rail.

This capacitor could also be your problem.

 

Check to make certain that the new power transistors are actually insulated from the heat sink. It is very easy to get the washers for the mounting screws off-center; and then the threads of the screw can short the transistor tab to the heat sink.

It LOOKS like everything is in place, but you still have a short circuit.

Measure the resistance from the mounting tab of each transistor to the heat sink. If you see less than about 10 Ohms resistance, you have found a problem.

 

Hello To all ,
Thank you for all your replies & Helps,

The amplifier is finally working well.
It seems during the de-soldering & re-soldering process of the Power transistors, a trace might have broken, i figured this out when i was comparing the voltage readings (which was fishy) from both the channel's removable board's pin connections (1-10), then i decided of removing the whole amp board & check if something was Short underneath (even check for power transistors making contact with the heat sink), when i turned the board upside down, Wallah!! i saw a broken trace which goes to pin 3 of one of the power transistor in the left channel , i fixed that , Checked for transistors making contact to the heat sink & reconnected the board , did a test run & every thing was fine, the 100 omh resistor doesn't heat anymore, the bass is good (no distortion).

Now, i'll try my best to totally avoid touching the Main Amp board.

 

Hello to all ,
Here are some pics of the amp (please ignore the dates in the pic as they are incorrect) .

Please note that the connector ports earlier were old soviet type, which were quiet impossible to use today, i modified it to modern ports.

The amp is Really powerful & offering Superb sound quality (clarity) .

Thanks to the following users for help & advises.

SGTWOOKIE , Thank you for co-operating & your patience.

STUDIOT , Thank you also for your help.

 

Nice to see someone gaining pleasure from their hobby.