Looking to see if anyone can help steer me in a different direction than I’ve been going with a Sansui G-5500. It belongs to a friend of mine who asked me to diagnose a problem that I could not duplicate, and once we knew it was pretty solid we decided to do a restoration on it; change out the caps, trim pots, full cleaning etc.
So this worked out originally, and the unit was perfectly fine after the work. A month or so later he told me it was popping through the speakers even at low volume, so I have it back here again.
I have not been able to duplicate the issue he was having, but instead somehow introduced a new one which was that the unit was now going into protection when I was about halfway up on the volume level (sinewave test). In playing around with stuff I’m not sure how I did it but I managed to blow the outputs on the right channel. So I replaced them with the NJW equivalent subs and once I knew those were ok I also replaced all the sketchy driver transistors that I didn’t feel needed to be done the first time around. Now I am getting the relay to click into protection at about a quarter of the volume. Same input level, and also still no right channel.
I’m not sure if I’m concentrating in the right area right now because I’m getting flustered on this one. Anyone here familiar with the G-5500 by chance? I did check the stupid stuff like open emitter resistors, and I have pulled all my replacement parts and double checked. I’ve also replaced the HA12002 protection IC because I thought maybe I had damaged it when I was cleaning the corrosive glue away on the board. All the voltages look fine there, as well as on both channel outputs I’m getting my +/- 43v. I’m just a bit stumped at the moment…
So this worked out originally, and the unit was perfectly fine after the work. A month or so later he told me it was popping through the speakers even at low volume, so I have it back here again.
I have not been able to duplicate the issue he was having, but instead somehow introduced a new one which was that the unit was now going into protection when I was about halfway up on the volume level (sinewave test). In playing around with stuff I’m not sure how I did it but I managed to blow the outputs on the right channel. So I replaced them with the NJW equivalent subs and once I knew those were ok I also replaced all the sketchy driver transistors that I didn’t feel needed to be done the first time around. Now I am getting the relay to click into protection at about a quarter of the volume. Same input level, and also still no right channel.
I’m not sure if I’m concentrating in the right area right now because I’m getting flustered on this one. Anyone here familiar with the G-5500 by chance? I did check the stupid stuff like open emitter resistors, and I have pulled all my replacement parts and double checked. I’ve also replaced the HA12002 protection IC because I thought maybe I had damaged it when I was cleaning the corrosive glue away on the board. All the voltages look fine there, as well as on both channel outputs I’m getting my +/- 43v. I’m just a bit stumped at the moment…
I can't help you with details of working on it... but I do have a rebuilt G7500 and I was involved in getting parts for the restoration.
The output transistors for the Sansui G series receivers were a "high speed" version. Somewhat unreliable and the design put them in a "hot valley"... there are no "substitutes" for them... and they are unobtanium... your only hope is to find someone who's parting a receiver with good output transistors.
If you replaced them with non high speed "subs" you are changing the sound of the receiver. It took us five or six months to find a replacement set... used from someone who had parted one.
Those output transistors are what makes the G series so good sounding (High Slew Rate). If you replace them with others, then it's likely not worth it.
The output transistors for the Sansui G series receivers were a "high speed" version. Somewhat unreliable and the design put them in a "hot valley"... there are no "substitutes" for them... and they are unobtanium... your only hope is to find someone who's parting a receiver with good output transistors.
If you replaced them with non high speed "subs" you are changing the sound of the receiver. It took us five or six months to find a replacement set... used from someone who had parted one.
Those output transistors are what makes the G series so good sounding (High Slew Rate). If you replace them with others, then it's likely not worth it.
I'm not sure about that one. I have read other threads where people have changed the outputs to NJW0281G/NJW0302G with no ill effects. I'm also not discounting what you're saying because clearly I have a problem that got worse after changing out the originals, I'm just thinking that if others have been able to make it work, then it should technically work, whether or not it changes the sound of the receiver.
Technically, you can swap the output transistors... in some cases you might have to tweak the circuit ( bias I guess ).... but the SOUND will change. That's how it was described to me. I didn't dwell on it. I had no interest on re-designing a vintage unit.
Those receivers were "High Slew Rate" designs. They output transistors like that are no longer made.
Yes, I guess you can swap the output transistors... but then you won't have the same sound. Anyways, hoping you fix the protection circuit.
Just my two cents.
On schematic find by me on the internet the slew-rate is noted to be 56V/µsec which is normal not fast. Fast means to over 100-150V/µsec.
An the transistors are 2SC2578 and 2SA1103 witch are 20Mhz. Most modern transistors for audio amplifiers are 30Mhz so I do not understood what is with first post of @tonyEE .
An the transistors are 2SC2578 and 2SA1103 witch are 20Mhz. Most modern transistors for audio amplifiers are 30Mhz so I do not understood what is with first post of @tonyEE .
In the late 70s, Japanese audio components went into a High Slew rate race.
The Sansui G series were advertised as such.
Those transistors are no longer being made.
If you want to replace the output transistors with "modern" types, well you have a different circuit and a different sound.
Which, IMHO, defeats the purpose of "fixing" a vintage component.
Again, IMHO, if you're going to "fix" a vintage component by redesigning it with new parts, you might as well spend the time building a nice XA252. The end result will sound FAR better. I ought to know, I got both a collection of rebuilt, to OEM, 70s receivers and "modern" amps. For clarity, the modern amps are far superior... but the vintage units, all of which are noted for being 'good sounding' (*) have a much darker sound.
(*) Why waste your time rebuilding a Radio Shack receiver?
The Sansui G series were advertised as such.
Those transistors are no longer being made.
If you want to replace the output transistors with "modern" types, well you have a different circuit and a different sound.
Which, IMHO, defeats the purpose of "fixing" a vintage component.
Again, IMHO, if you're going to "fix" a vintage component by redesigning it with new parts, you might as well spend the time building a nice XA252. The end result will sound FAR better. I ought to know, I got both a collection of rebuilt, to OEM, 70s receivers and "modern" amps. For clarity, the modern amps are far superior... but the vintage units, all of which are noted for being 'good sounding' (*) have a much darker sound.
(*) Why waste your time rebuilding a Radio Shack receiver?
I know this and you are right, but you did not specify what "High Slew rate" means to you. I just specified that this amplifier is noted in the service manual as having a slew rate of 56V/µsec, which is not high at all, but normal.
High slew rate amplifiers are those with slew rates over 80-100V/µsec, in fact I would include only those over 150-200V/µsec here.
Moreover, the original transistors are 20Mhz, which does not mean that they are slow but not very fast, and now you can easily find 30Mhz.
You can see some examples that are still produced in the link: https://www.onsemi.com/products/dis...lfjJ+NjB+MjAwfjI1MDIyNjJ+cmFuZ2V+Mn4zMH4zMH4=
An example that would fit is the NJW1302G and NJW3281G
In order not to unnecessarily prolong the discussion in a sterile direction, I specify that I have about 15-20 vintage equipment from the '70s-'90s, of which I think 10 are power audio amplifiers and some even fall into the "high slew-rate" category.
High slew rate amplifiers are those with slew rates over 80-100V/µsec, in fact I would include only those over 150-200V/µsec here.
Moreover, the original transistors are 20Mhz, which does not mean that they are slow but not very fast, and now you can easily find 30Mhz.
You can see some examples that are still produced in the link: https://www.onsemi.com/products/dis...lfjJ+NjB+MjAwfjI1MDIyNjJ+cmFuZ2V+Mn4zMH4zMH4=
An example that would fit is the NJW1302G and NJW3281G
In order not to unnecessarily prolong the discussion in a sterile direction, I specify that I have about 15-20 vintage equipment from the '70s-'90s, of which I think 10 are power audio amplifiers and some even fall into the "high slew-rate" category.
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OK.... you realize that I'm discussing "High Slew Rate" as it was known in the late 70s?
Compare this with say a '74 Marantz 2325... ( which I own one ) or a '76 Kenwood ( I also own one )...
When I discuss vintage components, I discuss then in contemporary terms. That's because when I have one of them rebuilt, it's done to OEM specs. No sense getting involved in redesigning old stuff when so much great, more modern designs exist.
Compare this with say a '74 Marantz 2325... ( which I own one ) or a '76 Kenwood ( I also own one )...
When I discuss vintage components, I discuss then in contemporary terms. That's because when I have one of them rebuilt, it's done to OEM specs. No sense getting involved in redesigning old stuff when so much great, more modern designs exist.
@sesebe yes. I was going to dive in deeper with the scope later to check something along those lines to see why the new parts are acting different. I was monitoring the protection IC pins with my meter, trying to see if there was some type of fluctuation right before the relay disengaged, but there was nothing obvious. Maybe the scope will tell me something. I'm still down a channel also, which, after I had started my re-work, found that it had already been messed with and outputs were changed out also, but it must have been done ages ago. Also, just a quick note, if I move the balance pot to the right channel (the one that's out), the relay will not kick out. It's only when there is an active signal and load on what is only the left channel right now. Also doesn't happen on just an input; has to have an active load connected, dummy or speaker.
There is a peculiar detail with this power amplifier stage - the high frequency feedback (via C17 capacitor) is not taken from the speaker output (junction of output transistors' emitter resistors) but "earlier" from the signal path.
So change in output transistors properties may introduce a phase shift in feedback chain that may end up in oscillation. It may happen or not happen - who knows exactly, your scope investigations perhaps will reveal something.
So change in output transistors properties may introduce a phase shift in feedback chain that may end up in oscillation. It may happen or not happen - who knows exactly, your scope investigations perhaps will reveal something.
Well, it's fixed... and both issues 100% MY fault (which actually makes me feel better about it).
1. Tripping into protection: I accidentally ordered and used 33ohm emitter resistors
. That'tl do it. Supposed to be 0.33ohm, and I KNEW that. I even looked at them multiple times and it still didn't phase me.
2. Channel out: I ripped the ribbon connector cable right out of the volume pot board and it happened to be hanging by a thread on just the left channel.
Another one put to bed. And thank you to everyone who assisted with my frustration.
1. Tripping into protection: I accidentally ordered and used 33ohm emitter resistors
. That'tl do it. Supposed to be 0.33ohm, and I KNEW that. I even looked at them multiple times and it still didn't phase me. 2. Channel out: I ripped the ribbon connector cable right out of the volume pot board
and it happened to be hanging by a thread on just the left channel.Another one put to bed. And thank you to everyone who assisted with my frustration.
