Here's one for the transistor design gurus here...
I've been tasked with the nightmare of rebuilding one of these. Originally, the customer didn't want to spend much to fix it, because he paid near 2 grand for it non-working. I took it on because I'd worked on several other Sansui receivers for him and they were relatively easy to repair.
This G22000 has numerous issues, including bad capacitors in the tuner, bad relays throughout and the main one, blown output and driver stages.
As these parts were no longer available, I spent many hours researching cross referenced parts.
What I chose was Pre drivers: MJE340/350. Drivers 2SA1668 and 2SC4382.
Outputs MJ21193/94.
Initial results were high notch distortion at lower power levels (2.4% THD with 0.5 vrms sine wave out. I spent a few hours revamping the bias circuit to get rid of the notch, but the maximum output is still only about 34 vrms as compared to 42 vrms for the original channel.
Since I selected matched parts for the drivers/pre drivers, the best match was in the lower part of the hfe range. I had some parts in the P junction that were high hfe on the curve tracer, but no N junction devices that would match, so I ended up using low hfe devices throughout the driver PCB.
I called the customer today and discussed the many problems and that the cost of fixing this right is going to be way past his original $300-500 budget. The problems extend to shorted caps in the tuner, bad relays throughout preamp and power amp, bad fan thermostat, dirty controls and a dirty step attenuator (volume). We managed to up the repair budget to $1400, though now customer is demanding the unit be perfect for that money. Thus, I must solve how to get 100 more watts out of the left channel. I'm currently getting about 136 watts into 8 ohms at clipping. Rails are 83 volts.
My hunch is the low hfe devices are preventing enough drive to the output stage. Possibly the original RET outputs had more gain. Many amplifiers have bigger rails for the drivers than the outputs to enable proper drive of outputs, but this amplifier has the same rail potential on both, so that may be a factor. The amplifier operates nicely, other than the lower power output in the rebuilt channel.
The remaining other issues is finding replacements for the relays that mute the power meters and mute the preamp output. They are sealed. The speaker relays are bad, too, but I might be able to remove them, disassemble and clean the contacts.
Any leads on where to get the same or equivalent relays would be a help, too. Thanks!
I've been tasked with the nightmare of rebuilding one of these. Originally, the customer didn't want to spend much to fix it, because he paid near 2 grand for it non-working. I took it on because I'd worked on several other Sansui receivers for him and they were relatively easy to repair.
This G22000 has numerous issues, including bad capacitors in the tuner, bad relays throughout and the main one, blown output and driver stages.
As these parts were no longer available, I spent many hours researching cross referenced parts.
What I chose was Pre drivers: MJE340/350. Drivers 2SA1668 and 2SC4382.
Outputs MJ21193/94.
Initial results were high notch distortion at lower power levels (2.4% THD with 0.5 vrms sine wave out. I spent a few hours revamping the bias circuit to get rid of the notch, but the maximum output is still only about 34 vrms as compared to 42 vrms for the original channel.
Since I selected matched parts for the drivers/pre drivers, the best match was in the lower part of the hfe range. I had some parts in the P junction that were high hfe on the curve tracer, but no N junction devices that would match, so I ended up using low hfe devices throughout the driver PCB.
I called the customer today and discussed the many problems and that the cost of fixing this right is going to be way past his original $300-500 budget. The problems extend to shorted caps in the tuner, bad relays throughout preamp and power amp, bad fan thermostat, dirty controls and a dirty step attenuator (volume). We managed to up the repair budget to $1400, though now customer is demanding the unit be perfect for that money. Thus, I must solve how to get 100 more watts out of the left channel. I'm currently getting about 136 watts into 8 ohms at clipping. Rails are 83 volts.
My hunch is the low hfe devices are preventing enough drive to the output stage. Possibly the original RET outputs had more gain. Many amplifiers have bigger rails for the drivers than the outputs to enable proper drive of outputs, but this amplifier has the same rail potential on both, so that may be a factor. The amplifier operates nicely, other than the lower power output in the rebuilt channel.
The remaining other issues is finding replacements for the relays that mute the power meters and mute the preamp output. They are sealed. The speaker relays are bad, too, but I might be able to remove them, disassemble and clean the contacts.
Any leads on where to get the same or equivalent relays would be a help, too. Thanks!
