The owner of the local electronics supply shop (Norvac) contacted me a couple of days ago as I had asked him to order me 4 cans of Caig F5, which by the way they went back to their old spray top, woohoo! He is constantly giving me parts I need for free and when I need things like this pot cleaner I like to give him the business.
When I went to pick them up, he asked if we could work out some type of deal. His brother has a Marantz 2220 that completely stopped working in one channel and he asked if I could fix it and exchange for the cleaner, plus he gave me some other things. I told him I would fix it, but I would also go ahead and do a bit of a restoration since it’s his brothers. so I’ve been through the entire amp, it got a full recap, new Zeners, some new transistors to replace the ones known to go faulty, etc.
Onto the driver board that’s when I saw it had a catastrophic failure. An electrolytic had completely exploded, there were multiple resistors that had burnt and gone open, the two outputs on that channel were shorted, and there are a couple of transistors that had gotten very hot and exploded themselves, also both emitter resistors are open.
I have already replaced all of the capacitors and all of the burnt resistors. I still need to go through the rest of the board board, I’m going to check every piece of silicon there is including the germanium diodes, 1N60s. The two transistors in red are the physically damaged.
I do know that the drivers are toast, they were originally 2SC1509 and 2SA777. I could either go KSC2383/KSA1013 or go a little overkill with TTC004b/TTA004b. Not sure with the original Ft being 60 MHz it being better to step down to 20 MHz or up to 100 MHz. I’m thinking the Toshiba devices would be the better way to go.
That isn’t too much of an issue, the one I’m having the most trouble deciding on is H704 which is a 2SC1175…
Dan
When I went to pick them up, he asked if we could work out some type of deal. His brother has a Marantz 2220 that completely stopped working in one channel and he asked if I could fix it and exchange for the cleaner, plus he gave me some other things. I told him I would fix it, but I would also go ahead and do a bit of a restoration since it’s his brothers. so I’ve been through the entire amp, it got a full recap, new Zeners, some new transistors to replace the ones known to go faulty, etc.
Onto the driver board that’s when I saw it had a catastrophic failure. An electrolytic had completely exploded, there were multiple resistors that had burnt and gone open, the two outputs on that channel were shorted, and there are a couple of transistors that had gotten very hot and exploded themselves, also both emitter resistors are open.
I have already replaced all of the capacitors and all of the burnt resistors. I still need to go through the rest of the board board, I’m going to check every piece of silicon there is including the germanium diodes, 1N60s. The two transistors in red are the physically damaged.
I do know that the drivers are toast, they were originally 2SC1509 and 2SA777. I could either go KSC2383/KSA1013 or go a little overkill with TTC004b/TTA004b. Not sure with the original Ft being 60 MHz it being better to step down to 20 MHz or up to 100 MHz. I’m thinking the Toshiba devices would be the better way to go.
That isn’t too much of an issue, the one I’m having the most trouble deciding on is H704 which is a 2SC1175…
Dan
H704 is a 2SC1175, I’ve seen multiple places on Audiokarma that the KSC2383 is the recommended replacement.
Is going from 170 MHz to 20 a good idea when there are other possibilities?
These two look better, though still not up to the 170 MHz. The KSC1815 having slightly lower rated Ic, may not be an issue.
I was wondering about the 2N5551C, but is going from 170 MHz to 300 too big of a jump? I worry about the stability, but if people recommend dropping by 150 MHz then maybe it doesn’t matter all that much in this position.
The Zetex was another one I was thinking would make a good replacement. Ft is quite close and it’s overkill elsewhere. My only concern here is the gain. It’s going to be a huge jump. The lowest ZTX694b I have will probably measure 550-600 on a Peak Atlas DCA75.
Any other recommendations or suggestions as to which I should use?
Dan
Is going from 170 MHz to 20 a good idea when there are other possibilities?
These two look better, though still not up to the 170 MHz. The KSC1815 having slightly lower rated Ic, may not be an issue.
I was wondering about the 2N5551C, but is going from 170 MHz to 300 too big of a jump? I worry about the stability, but if people recommend dropping by 150 MHz then maybe it doesn’t matter all that much in this position.
The Zetex was another one I was thinking would make a good replacement. Ft is quite close and it’s overkill elsewhere. My only concern here is the gain. It’s going to be a huge jump. The lowest ZTX694b I have will probably measure 550-600 on a Peak Atlas DCA75.
Any other recommendations or suggestions as to which I should use?
Dan
More Hfe is probably a good thing in this circuit! More available feedback should reduce distortion.
The capacitance of the ZTX851 is a lot higher than the other options, not sure if that's an issue at all or not, considering the compensation caps around it...
Feed it square waves and see what happens. /shrug
The capacitance of the ZTX851 is a lot higher than the other options, not sure if that's an issue at all or not, considering the compensation caps around it...
Feed it square waves and see what happens. /shrug