Technics SU-G70 Integrated

[DonQuixote99]

Just got one at Goodwill. Anyone know about it? Info on the web is sparse, can't find published specs. Board chat says it's 120 WPC, and based on the power consumption of 430 watts that's credible. Those that have them seem to like them. Sounds good in brief initial testing--actually made me like a pair of Infinity RS-2001s! Nothing else ever managed that....

One person called the sound 'bright;' haven't listened enough to have an opinion yet myself. There's a fan on the back, and on the front it says "New Class A." Someone said this is 'fake' class A. Hmmm....

One thing I notice: on the back it specifies 8 and 16 ohm speakers. 4 ohm conspicuously not mentioned.

It's got some early-days surround function, some Dolby 'delayed rear' thing. Probably won't mess with that.

I opened it up and the component set is not of a familiar sort to me: the amplifier devices consist of two big heat-sinked modules. The are labled "Stereo Power Amplifier SVI 3206 A" and "SVI 3100 B Stereo Power Amplifier."

PICS:

 

[rally]

taken from brochure for system SC-S310;
output power (20Hz- 20 kHz, 0.05 THD) 110W per channel (8 ohms)
total harmonic distortion (half power at 1 kHz) 0.03% (8 ohms)
Frequency response phono RIAA standard curve +/- 0.8 dB
tuner/cd/tape/vcr1/vcr2/tv 10Hz-80 kHz (-3 dB)
S/N (IHF A) phono 71 dB (73 dB, IHF '66)
tuner/cd/tape/vcr1/vcr2/tv 75 dB (94 dB, IHF '66)
16 15/16" x 5 5/32" x 11 23/32" 19.4 lbs
total harmonic distortion is measured by the digital spectrum analyzer (HP 3045 System)

I added a computer fan as a precaution to the overheating tendancy and have
had no problems (so far)

 

[vintageboy]

I have G95 home that is 130wpc. These amps can handle a lot

 

[SVI2004A]

Those G70s were the last of the original SVI amps... The 3206A is a 130Wpc power amp, New class A is a sliding bias setup. These are a great amp electronically, but definately where Technics were cutting corners. Points here are the plastic fronts, the cheaper phono stages ( no mm/mc sel), the questionable ribbon interconnects to the power xfmr ant the biggest issue that TINY heatsink! <this definately is why no 4 ohm speakers>

Keeping your lovely amp alive...
The biggest threat to these amps are heat. As you can see the heatsink isnt much bigger than the SVI bolted to it. Technics answer to compensate for that tiny heatsink was to tack in a cooling fan. The problem with this is over the years, the bearings dry up which strains the motor, making it draw more current which in turn takes out the fan drive transistors. Other case dust/bad contact in the comutator in the motor makes it open circuit. Either way this equals a stopped fan. If you are playing it louder the SVI will happily keep amplifying till it gets so hot, that the output transistors actually desolder themselves and slide down into other output transistors or drive components (BLOCKSLIDE) terminal for such a lovely IC.

I will add a pic of this soon

Simple test... Run the amp with no speakers and play some music through it. With speakers A or B switch on when the power meters get around halfway up, the fan should be kicking in... Over the 10w indicator it should be blowing out s nice breeze.


If thats not happening check the fan motor and fan drive transistors

I am always here to help with any inquiry

Regards Baily

 

[DonQuixote99]

taken from brochure for system SC-S310;
output power (20Hz- 20 kHz, 0.05 THD) 110W per channel (8 ohms)
total harmonic distortion (half power at 1 kHz) 0.03% (8 ohms)
Frequency response phono RIAA standard curve +/- 0.8 dB
tuner/cd/tape/vcr1/vcr2/tv 10Hz-80 kHz (-3 dB)
S/N (IHF A) phono 71 dB (73 dB, IHF '66)
tuner/cd/tape/vcr1/vcr2/tv 75 dB (94 dB, IHF '66)
16 15/16" x 5 5/32" x 11 23/32" 19.4 lbs
total harmonic distortion is measured by the digital spectrum analyzer (HP 3045 System)

I added a computer fan as a precaution to the overheating tendancy and have
had no problems (so far)

Thanks Rally. I saw a ad that indicated the G70 was sold as part of a system stack, but didn't know it's designation.

 

[DonQuixote99]

Those G70s were the last of the original SVI amps... The 3206A is a 130Wpc power amp, New class A is a sliding bias setup. These are a great amp electronically, but definately where Technics were cutting corners. Points here are the plastic fronts, the cheaper phono stages ( no mm/mc sel), the questionable ribbon interconnects to the power xfmr ant the biggest issue that TINY heatsink! <this definately is why no 4 ohm speakers>

Keeping your lovely amp alive...
The biggest threat to these amps are heat. As you can see the heatsink isnt much bigger than the SVI bolted to it. Technics answer to compensate for that tiny heatsink was to tack in a cooling fan. The problem with this is over the years, the bearings dry up which strains the motor, making it draw more current which in turn takes out the fan drive transistors. Other case dust/bad contact in the comutator in the motor makes it open circuit. Either way this equals a stopped fan. If you are playing it louder the SVI will happily keep amplifying till it gets so hot, that the output transistors actually desolder themselves and slide down into other output transistors or drive components (BLOCKSLIDE) terminal for such a lovely IC.

I will add a pic of this soon

Simple test... Run the amp with no speakers and play some music through it. With speakers A or B switch on when the power meters get around halfway up, the fan should be kicking in... Over the 10w indicator it should be blowing out s nice breeze.


If thats not happening check the fan motor and fan drive transistors

I am always here to help with any inquiry

Regards Baily

Wow, lots of good info, thanks.

I've seen the fan running some, but I'll do the test you mention. Also sounds like removing dust a good idea. Is it possible to relube those bearings? It seems like a nice quiet fan.

The SVi seems to be an example of what I know as a 'hybrid' module, combining IC and discrete components. Very impressive technology for consumer electronics.

I've got a pre-amp and equalizer feeding into the 'main in' now, using the G70 as a power amp only. Phono stage therefore not an issue. Have to see what speakers it likes best. Since it did good with the little Infinities, I think I need to hurry up and refoam the RS-6s I've got.

 

[riverrat]

I picked up a somewhat earlier SU-V9 for $25 earlier this year. Seller said he thought it had a grounding issue, turned out it just needed a good cleaning. Compact, HEAVY amp with a number of nice features. It is also "New Class A".

I certainly feel it was worth $25. It sounds very nice and pushed my Apogee Centaurs pretty well. I think some of these Technics amps are very under-rated and go under the radar of most people. A lot of bang for the vintage buck here.

 

[SVI2004A]

From the looks of your amp, its been well kept. For the fan motor use a light machine oil like sweing machine oil etc

 

[DonQuixote99]

Oh darn.

The speakers I was hoping to use with this amp, Infinity RS-6s, aren't RS-6s. I took a stylized 'b' for a '6.' They are the earlier model RSb.

Specs are very similar, except for impedence. RS-6, 6 Ohm; RSb, 4 Ohm.

I don't suppose just putting a resistor on the + terminal would work real well....

 

[justdreamin]

I just picked up the g70 amp with what looks like the full meal deal of technics matching components; st-k50 tuner, sl-bd270 turntable, rs-tr167 double cassette, and sh-8017 eq, pair of sb-a51 speakers. It was all free because the amp doesn't power on.

So that's the issue. It clicks inside as if it's going to power up but it doesn't. All the other components work. Just wondering if there are any ideas as to what to look for...or what to tell somebody that knows what they're doing to look for

Thanks in advance!!!

 

[SVI2004A]

Resistor failure Green resistor to the left hand side of the relay R717 iirc the other resistors are R6**... Components in the 700s are power supply related... The resistor that failed feeds the +15V regulator, This resistor often is what fails in this series of amp... The click you hear is indicating all is well with the power amp. Nice score

 

[justdreamin]

Resistor failure Green resistor to the left hand side of the relay R717 iirc the other resistors are R6**... Components in the 700s are power supply related... The resistor that failed feeds the +15V regulator, This resistor often is what fails in this series of amp... The click you hear is indicating all is well with the power amp. Nice score

Hey, thank you so much for your reply! I really appreciate it!

 

[justdreamin]

Hi again. Is there any chance that you know what the resistance is for the 4 R7** resistors? When I try to read the band colors and type them into the "idiot proof" resistor calculator I don't get a standard reading. I can't really determine the colors... I'm getting 13ohm on the R771 and 17ohm on the R717. Also, do you know what the R6**'s are for? Thank you for your time!

 

[SVI2004A]

The green resistor to the left (xfmr side) is a 22 ohm fusible 1/2 w

The other 2 green ones R6** are relay related ( volt drop to have 24v to the relay)

 

[pioneersx780]

I had one of these about 6 years ago. Great sounding and powerful amp! Mine however was in operation when it failed. Like mentioned above the fan had stopped when the amp was being driven at a high volume, the amp and casing got so hot that it actually burned skin. After it cooled down it would clip at a low vol and so out to the garage it went. Honestly i don't think I took it when I moved.

 

[Dale Korsmo]

Happy to see somebody has some experience with this unit. I have an SU-G70P-K that has not been used in about 6 years. When you first turn it on, it either fires right up and works as it should, or you hear the relay click, but nothing happens. When it does fire up, the display is bright and clear and all functions seem to work, the fan even turns, but after a few minutes, the display goes blank and within another minute, the audio drops to mostly low volume static. Wondering if this could also be the green resistor mentioned earlier. Also, to clear up some confusion, on my unit, the green resistor next to the relay is R771, not R717. R717 is on the front left corner of the PC board. Finally, where does one source these special resistors? The manual says to only use their parts, but I doubt they are available any longer.

 

[SVI2004A]

The asterisk / safety note is because it's a fusible resistor, having said that once they fail they don't work again.... your fault is intermittent, I'd check regulator Q701 for dry joints - check all regulators whilst there. Yeah R771 1/2 watt fusible have come across sets with 22 ohms and sets with 12 ohms. G50/70 based on same pcb.

 

[Wraith272]

I grew up in a house that had a system with this G70 amp and recently inherited it, but the amp seems to randomly switch input to the tuner and reset the volume, audio also sounds a little crackly when first powered up. Are these symptoms that could be related to that common resistor failure mentioned earlier in the thread? I'm pretty mechanically inclined but don't know where to start with troubleshooting an amp

 

[SVI2004A]

Sounds like input selector resetting... default is tuner mode

I would remove the front panel of the amp, check for dry joints on the front pcb - and spray a little contact cleaner in the connector plugs on replacing front end...
See how it goes from there...

 

[kretinus]

as a side note, I've encountered a number of older IR remote controlled devices that will actually get interference from CF bulbs, one motel I worked at we had to put filters over the sensor windows of 120 new TVs because of the issue.