SONY TA 70 stereo amplifier circuit required - UK Vintage Radio Repair and Restoration Discussion Forum

don200002 · 17th Jan 2013, 3:48 pm

Hi All,
My son came over last week with a Sony amp he had found in a skip. Its a Sony TA 70 stereo hi fi amp with one channel down. On initial inspection the outout transistors check out ok but I have found a 1 ohm resistor open cicuit and a 2sc634a short. These have been replaced and I now have some response from the duff channel albeit very low. On further inspection I have some strange voltages around some of the other transistors by comparison to the working channel. At this point I can carry on checking components but it would be much easier with a circuit diagram, can anyone help?
Thanks,
Don.

John_BS · 17th Jan 2013, 9:06 pm

Is it a TA-F70?

John

don200002 · 17th Jan 2013, 9:21 pm

Hi John,
Thanks for looking but it is definately a TA-70. I have searched the internet and found one or two for sale but no sign of a circuit diagram anywhere. It seems the only option is to remove and check the components individually, (I hate working blind) but thanks for your help and interest.

Don

sp10mk11 · 17th Jan 2013, 11:59 pm

These are little 8 watt per-channel amps i have had one as my workshop amp for more years than i care to remember, i havent a circuit diagram but they are simple to repair if blown as had to do mine many years ago.
and yes it is the black fronted TA-70 as you say
Good luck

Big jim · 24th Jan 2013, 7:18 pm

Hi. I have the manual I will scan it up for you this weekend.

Regards, Jim.

don200002 · 27th Jan 2013, 8:43 pm

Hi All,
My apologies for not checking the post for a couple of days and thanks Jim for the offer of a scan which I would still like although I have now got the amp working it would probably be very useful in the future.
On further inspection I found two more 2SC634A transistors faulty which were replaced using BC547s. The amp was then run up using the Variac and it came to life at about 110volts. However, increasing the voltage to about 125volts produced that nasty hum which tells you something is about to go up in smoke. I switched off quickly to find the two 2SD292 output transistors were running very warm, (so much for me saying they checked out OK in the first place). These were replaced with a couple of TIP41Cs and a shot of switch cleaner in the pots completed the repair. It has been running now for about 4 hours, the TIP41s are only just warm and although it is not a particularly powerful amp the sound quality is excellent.
Thanks everyone for your help and yes Jim I would like a copy of that scan.
Don.

Sony TA70 man · 13th Mar 2015, 6:43 pm

Hi there,

Sorry I know the thread is over two years old now but I am currently working on a very nice TA-70 (two 2SD292 transistors running very hot). I desperately need a schematic but its seems impossible to find. Unfortunately I missed one on ebay a few weeks back . just wondered if anyone could oblige with a scanned copy?

Many thanks,
Ray

sp10mk11 · 15th Mar 2015, 1:03 pm

Just out of interest these 8 watt amps were used in a few other models by Sony, the HMK33 music centre being one of them. Maybe a search for a manual for that model will help.

Gary

yoel.markus · 12th Feb 2016, 8:40 pm

Hi All,
I've inherited a Sony TA-70 unit that hasn't ever been updated/upgraded since it was bought in the 70s. I am looking for a copy of the schematic please so that I can do some preventative updates to make it last for another few decades.
Has anyone ever added a bluetooth module to this amplifier?

17th Jan 2013, 3:48 pm	#1
don200002 Pentode Join Date: Sep 2011 Location: Bideford, Devon, UK. Posts: 196	SONY TA 70 stereo amplifier circuit required Hi All, My son came over last week with a Sony amp he had found in a skip. Its a Sony TA 70 stereo hi fi amp with one channel down. On initial inspection the outout transistors check out ok but I have found a 1 ohm resistor open cicuit and a 2sc634a short. These have been replaced and I now have some response from the duff channel albeit very low. On further inspection I have some strange voltages around some of the other transistors by comparison to the working channel. At this point I can carry on checking components but it would be much easier with a circuit diagram, can anyone help? Thanks, Don.

17th Jan 2013, 9:21 pm	#3
don200002 Pentode Join Date: Sep 2011 Location: Bideford, Devon, UK. Posts: 196	Re: SONY TA 70 stereo amplifier circuit required Hi John, Thanks for looking but it is definately a TA-70. I have searched the internet and found one or two for sale but no sign of a circuit diagram anywhere. It seems the only option is to remove and check the components individually, (I hate working blind) but thanks for your help and interest. Don

17th Jan 2013, 11:59 pm	#4
sp10mk11 Octode Join Date: Feb 2009 Location: Cornwall, UK. Posts: 1,275	Re: SONY TA 70 stereo amplifier circuit required These are little 8 watt per-channel amps i have had one as my workshop amp for more years than i care to remember, i havent a circuit diagram but they are simple to repair if blown as had to do mine many years ago. and yes it is the black fronted TA-70 as you say Good luck

24th Jan 2013, 7:18 pm	#5
Big jim Tetrode Join Date: Sep 2006 Location: South London, UK. Posts: 86	Re: SONY TA 70 stereo amplifier circuit required Hi. I have the manual I will scan it up for you this weekend. Regards, Jim.

27th Jan 2013, 8:43 pm	#6
don200002 Pentode Join Date: Sep 2011 Location: Bideford, Devon, UK. Posts: 196	Re: SONY TA 70 stereo amplifier circuit required Hi All, My apologies for not checking the post for a couple of days and thanks Jim for the offer of a scan which I would still like although I have now got the amp working it would probably be very useful in the future. On further inspection I found two more 2SC634A transistors faulty which were replaced using BC547s. The amp was then run up using the Variac and it came to life at about 110volts. However, increasing the voltage to about 125volts produced that nasty hum which tells you something is about to go up in smoke. I switched off quickly to find the two 2SD292 output transistors were running very warm, (so much for me saying they checked out OK in the first place). These were replaced with a couple of TIP41Cs and a shot of switch cleaner in the pots completed the repair. It has been running now for about 4 hours, the TIP41s are only just warm and although it is not a particularly powerful amp the sound quality is excellent. Thanks everyone for your help and yes Jim I would like a copy of that scan. Don.

13th Mar 2015, 6:43 pm	#7
Sony TA70 man Retired Dormant Member Join Date: Mar 2015 Location: Wolverhampton, West Midlands, UK. Posts: 1	Re: SONY TA 70 stereo amplifier circuit required Hi there, Sorry I know the thread is over two years old now but I am currently working on a very nice TA-70 (two 2SD292 transistors running very hot). I desperately need a schematic but its seems impossible to find. Unfortunately I missed one on ebay a few weeks back . just wondered if anyone could oblige with a scanned copy? Many thanks, Ray

15th Mar 2015, 1:03 pm	#8
sp10mk11 Octode Join Date: Feb 2009 Location: Cornwall, UK. Posts: 1,275	Re: SONY TA 70 stereo amplifier circuit required Just out of interest these 8 watt amps were used in a few other models by Sony, the HMK33 music centre being one of them. Maybe a search for a manual for that model will help. Gary

12th Feb 2016, 8:40 pm	#9
yoel.markus Retired Dormant Member Join Date: Feb 2016 Location: Toronto, Ontario, Canada Posts: 1	Re: SONY TA 70 stereo amplifier circuit required Hi All, I've inherited a Sony TA-70 unit that hasn't ever been updated/upgraded since it was bought in the 70s. I am looking for a copy of the schematic please so that I can do some preventative updates to make it last for another few decades. Has anyone ever added a bluetooth module to this amplifier?