hopjohn
Silver Face
I'm working through a KR-7600 and thought I would share a few modifications ideas that I implemented.
Lamps
Having worked on many Sansui Tuners and also the KR-9600 I've come to dislike the Stanley rubber based 8V 300mA lamps that mount on the two posts. These lamps have no base to them on their own so the only way to provide an original fit is to use some type of G3.5 globe lamp and remove the bases of those which is a PITA. If you're successful in removing the lamp you likely still have to solder on longer leads to make it work.
Going the LED route is okay and I've been successful putting 10mm style LEDs in place of these. It's been a while so I don't recall all of the details, but the end result is always a compromise to incandescent lighting which gives you the nice warm glow you'd expect from vintage gear.
Moving on to the solution. I decided to use #50 7.5V 220mA lamps which have E10 bases. I incorporate them by using an E10 socket with solder tabs that extend outward 180 degrees from one another. These can be found on that auction site in lots of 10. One tab has the perfect length for mounting. The other needs to be bent up and then out again for the correct spacing to slide onto the posts and be soldered on (Hint: abrade the posts first or you'll have trouble getting the solder to take). Adding some heat shrink to the base body and also the posts eliminates any potential for shorts. The height will be a bit greater once the bulb is installed compared with the originals but on the 7600 (and probably the 9600 as well) there is plenty of depth within the lamp assembly to spare so there are no issues with fit.
Filter cap ground strap
The 7600 has some healthy sized filter caps (12,000uF 63V) but I think the grounding strap on them is a bit wimpy. In place of the original braided strap I used a nice piece of solid core copper from some industrial Romex and soldered two ring terminals to each end. The copper strap is wound around the chassis tang and soldered up with a high wattage iron.
Original
Replacement
Moving the regulators off board
The regulators on the KR-7600 on are in close proximity to several resistors which get pretty darn hot. Qk1 is particularly vulnerable and is why it is given such a large heat-sink. Rather than try to keep those cool next to components that will always run hot, I've moved them off board underneath the PS.
I make use of the heat-sink from the original odd-ball rectifier which I had replaced. There are three holes in the chassis rail where the PS screws down, but only 2 holes are used so adding a third hole through the PS board allows me to take advantage of that hole and mount the heat-sink. Both regulators are then isolated with mica and plastic shoulder washers. After adding some thermal compound I screw them into the existing threaded holes. I follow that up by adding some split washers, nuts, and thread lock to the back to make sure they stay in place. Using some hook-up wire I route the appropriate BCE connections to the board and tidy it up with some heat-shrink insulation.
Lamps
Having worked on many Sansui Tuners and also the KR-9600 I've come to dislike the Stanley rubber based 8V 300mA lamps that mount on the two posts. These lamps have no base to them on their own so the only way to provide an original fit is to use some type of G3.5 globe lamp and remove the bases of those which is a PITA. If you're successful in removing the lamp you likely still have to solder on longer leads to make it work.
Going the LED route is okay and I've been successful putting 10mm style LEDs in place of these. It's been a while so I don't recall all of the details, but the end result is always a compromise to incandescent lighting which gives you the nice warm glow you'd expect from vintage gear.
Moving on to the solution. I decided to use #50 7.5V 220mA lamps which have E10 bases. I incorporate them by using an E10 socket with solder tabs that extend outward 180 degrees from one another. These can be found on that auction site in lots of 10. One tab has the perfect length for mounting. The other needs to be bent up and then out again for the correct spacing to slide onto the posts and be soldered on (Hint: abrade the posts first or you'll have trouble getting the solder to take). Adding some heat shrink to the base body and also the posts eliminates any potential for shorts. The height will be a bit greater once the bulb is installed compared with the originals but on the 7600 (and probably the 9600 as well) there is plenty of depth within the lamp assembly to spare so there are no issues with fit.
Filter cap ground strap
The 7600 has some healthy sized filter caps (12,000uF 63V) but I think the grounding strap on them is a bit wimpy. In place of the original braided strap I used a nice piece of solid core copper from some industrial Romex and soldered two ring terminals to each end. The copper strap is wound around the chassis tang and soldered up with a high wattage iron.
Original
Replacement
Moving the regulators off board
The regulators on the KR-7600 on are in close proximity to several resistors which get pretty darn hot. Qk1 is particularly vulnerable and is why it is given such a large heat-sink. Rather than try to keep those cool next to components that will always run hot, I've moved them off board underneath the PS.
I make use of the heat-sink from the original odd-ball rectifier which I had replaced. There are three holes in the chassis rail where the PS screws down, but only 2 holes are used so adding a third hole through the PS board allows me to take advantage of that hole and mount the heat-sink. Both regulators are then isolated with mica and plastic shoulder washers. After adding some thermal compound I screw them into the existing threaded holes. I follow that up by adding some split washers, nuts, and thread lock to the back to make sure they stay in place. Using some hook-up wire I route the appropriate BCE connections to the board and tidy it up with some heat-shrink insulation.
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