'74 Sony TA-1055 Recapping Project

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#41
Original resistors are always 0.25 W on these old amps. The only exception is if the resistors are huge - then they might be 1 W parts.

It doesn't matter what you use, wattage rating or resistor type. Just get whatever you can find of the intended values.
 
#43
The new resistors have arrived, I've put the proper value Rs in place. Have also replaced some of the caps, all I have left is the main supply caps, and the smaller ones that will be replaced with film caps. I fired the amp thru the DBT and it shows that the amp is working well. I'll probably finish everything by tonight and have a listen by the weekend.
 
#47
Mooly said:
Pleased to hear you are pleased 🙂 Its good fun bringing old gear back up to scratch.

Enjoy the amp.
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Thanks Mooly. This amp is beginner-friendly, and yet very satisfying. Thanks for your kind assistance.
Trileru said:
How does it sound?
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Bob, the amp sounds like it was, well, new! Very powerful, both channels are now balanced, the tonal range are also very balanced, I just set the volume and put the bass and treble at 0 and I'm happy. Bass section has changed a lot, more power and articulation. I played it overnight non stop, so far it's been running 11 hours or so at low volume and it's working nicely.
Thank you so much for steering me in this direction and guiding me thru the recapping stage.
 
#49
Please enlight me about DC offset. I measured my amp using a method explained here
When I got the amp it measured 90mV on the left channel and 10mV on the right channel. After I recapped and installed new transistors, they measured -99mV on the left and -8.5mV on the right channel. So basically the same figures, only this time it's negative value.

My questions: Does DC offset affect sound and performance of the amp? Do I measure the amp after it's been turned on/playing for some time, or measure it cold? What other parts do you suggest me to replace?

This may explain why the amp sometimes only play on the right channel especially at low volume. Usually quickly switching between input modes take care of it, but it may be a good idea to fix it properly.

Thanks.
 
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#50
The method is fine. Historically, DC offsets of up to around a 100mv were always considered acceptable. Its only in recent years that amps have been developed with more attention paid to DC stability... and an old design like this just isn't one of them. It will wander with temperature.

The normal levels of offset has no effect on sound quality.

Swapping the input transistors around might get you a lower value but you would have to be prepared for quite a bit of trial and error.
 
#54
Gents, this amp was left unused for more than a year, and when I tried to fire it up, it keeps blowing a fuse. I did some reading and came to a conclusion that the output transistor is dead. In order to check the condition of the transistor, I need to take it out of the circuit and measure, right?
Original transistor is 2SC1061, I used MJE15032 as replacement. Could it be the replacement is not suitable? I might look for TIP41C and replace all four. What else should I check?
As you can probably see from the pages back, I humbly need some handholding.
Thank you in advance.
 
#58
Most conventional linear amps with conventional power supplies should be fine on a variac.

Exceptions could include depletion mode FET output stages (like the original Sony VFET), class D amps and amps using switching power supplies.
 
#59
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