mhz
New Member
Hello! I am new to AK but have been around quite a bit and have to thank everyone for all the great information here which has helped me a ton.
I recently picked up a Marantz 2238 (non-B) in need of some care from a local record store. Don't think it has ever been serviced before; lamps were mostly out and components were all original. When I got it one of the channels was at low volume cutting in/out but thankfully that turned out to be a combination of dirty pots and a bad aux cable so apart from a general restoration I didn't seem to have any major issues to figure out.
I bought a restoration kit with all the replacement caps along with some new trimpots and transistors. I'm a beginner with this sort of thing and felt more comfortable getting preselected components the first time around instead of matching them myself. After working through the filter caps, power supply, and tone board things are already sounding better (the filter caps made an instant difference, old ones were down to 8500μF); however, I left out the replacement transistors for now.
The seller included matching sets of 4x KSC1845 and 4x KSA992 transistors to replace the original 2SC1328 and 2SA722 transistors on the preamp/tone board, respectively.
They also included another 6x KSA992 transistors to replace both the original 2SA722 and 2SA733 transistors on the main amp.
Finally, there are another 6x KSC1845s to replace the 2SC1328s on the phono board, though I don't plan to use that much.
I wouldn't even think of replacing any of the transistors if there was no room for improvement but I do hear a light white noise in the background when I'm not playing audio. The noise is on both channels and amplifies with increased volume. Although it isn't exactly disruptive, it is noticeable without much effort when if I put my ears near the speakers.
I am worried about a few things though. Although a few threads here do recommend the KSC1845 and KSC992 transistors as replacements for the originals in question, other threads warn that replacing transistors with non-original parts can require resistor changes (not included with the components I have) or cause some kind of oscillation. I am not familiar with transistor specifications or circuit design so I can't really determine if there would be any issues here. Though the seller seems pretty experienced with restorations, I don't want to start changing these things out without double checking first. Some posts say that by desoldering one of these transistors you basically make it unreliable for future use with the heat which also makes me worried that if I come across an issue using the replacements there is no return.
Anyone here replace these transistors before with modern substitutes with improvement in noise or sound or have any issues after doing so? Any advice is welcome.
Also, sort of related question: is it normal for the power supply transistor (2SD330D, in one of the pictures) to get extremely hot? Obviously it is meant to give off a fair amount of heat since it is screwed against a heatsink but that heatsink burns to the touch after a few minutes of use. Power supply stays exactly on point at 35.0V during adjustments though so the board seems to be working good, just not sure how much heat is normal.
I will probably at least finish recapping the main amp and listen again before making any decisions but would like to take out as much noise as possible.
Excuse the all the dust in the pictures, some of it is just cloudy old glue on the PCB and I'm going to give the rest a more thorough cleaning later.
I recently picked up a Marantz 2238 (non-B) in need of some care from a local record store. Don't think it has ever been serviced before; lamps were mostly out and components were all original. When I got it one of the channels was at low volume cutting in/out but thankfully that turned out to be a combination of dirty pots and a bad aux cable so apart from a general restoration I didn't seem to have any major issues to figure out.
I bought a restoration kit with all the replacement caps along with some new trimpots and transistors. I'm a beginner with this sort of thing and felt more comfortable getting preselected components the first time around instead of matching them myself. After working through the filter caps, power supply, and tone board things are already sounding better (the filter caps made an instant difference, old ones were down to 8500μF); however, I left out the replacement transistors for now.
The seller included matching sets of 4x KSC1845 and 4x KSA992 transistors to replace the original 2SC1328 and 2SA722 transistors on the preamp/tone board, respectively.
They also included another 6x KSA992 transistors to replace both the original 2SA722 and 2SA733 transistors on the main amp.
Finally, there are another 6x KSC1845s to replace the 2SC1328s on the phono board, though I don't plan to use that much.
I wouldn't even think of replacing any of the transistors if there was no room for improvement but I do hear a light white noise in the background when I'm not playing audio. The noise is on both channels and amplifies with increased volume. Although it isn't exactly disruptive, it is noticeable without much effort when if I put my ears near the speakers.
I am worried about a few things though. Although a few threads here do recommend the KSC1845 and KSC992 transistors as replacements for the originals in question, other threads warn that replacing transistors with non-original parts can require resistor changes (not included with the components I have) or cause some kind of oscillation. I am not familiar with transistor specifications or circuit design so I can't really determine if there would be any issues here. Though the seller seems pretty experienced with restorations, I don't want to start changing these things out without double checking first. Some posts say that by desoldering one of these transistors you basically make it unreliable for future use with the heat which also makes me worried that if I come across an issue using the replacements there is no return.
Anyone here replace these transistors before with modern substitutes with improvement in noise or sound or have any issues after doing so? Any advice is welcome.
Also, sort of related question: is it normal for the power supply transistor (2SD330D, in one of the pictures) to get extremely hot? Obviously it is meant to give off a fair amount of heat since it is screwed against a heatsink but that heatsink burns to the touch after a few minutes of use. Power supply stays exactly on point at 35.0V during adjustments though so the board seems to be working good, just not sure how much heat is normal.
I will probably at least finish recapping the main amp and listen again before making any decisions but would like to take out as much noise as possible.
Excuse the all the dust in the pictures, some of it is just cloudy old glue on the PCB and I'm going to give the rest a more thorough cleaning later.
