Scott LC-21

cduarte

cduarte

Well-Known Member
recently picked up a scott lc21 in a trade. It definitely fills a need as I have far more power amplifiers than preamps. It's already been rebuilt, but I'd like to perform some additional mods including the improved heyboer power transformer, and possibly replacing the multi section capacitors with higher capacitance. I'll be converting the tube rectifier to solid state, and adding an inrush limiter. I may also replace the volume pot with an alps. So far it sounds great with one of my rebuilt mc225s, I'll also be trying it with my dynaco st70 and eventually my heathkit w4-am and w4-b once I'm done rebuilding them. If anyone has a schematic, or the original kit documentation it would be greatly appreciated.

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Modifying it will reduce it's value,,,just sayin... If transformer is OK I would leave the rectifier and transformer,the selenium filament rectifier could be changed as well as electrolytic and coupling caps.If the volume control is good I would leave it,as the power switch is part of it.
 
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s-petersen said:
Modifying it will reduce it's value,,,just sayin... If transformer is OK I would leave the rectifier and transformer,the selenium filament rectifier could be changed as well as electrolytic and coupling caps.If the volume control is good I would leave it,as the power switch is part of it.
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resale is the last possible thing I'm concerned with, I listen and rebuild systems for friends. Sound quality matters to me, and my mods will be invisible from the outside. This one has mostly been rebuilt, but there are 2 original caps in the stereo switch .047uf/400v that will be replaced with film or russian pio. The original filter cap is still there and it looks to be a 20/20/20/10uf@450. Once I go to SS rectification, I can go much higher on those values, maybe even an 80/40/30/20@550v which I happen to have. Not sure what the can cap is with the clamp, I'll have to measure it, since it has no markings at all. The 3rd original can cap was 1000uf/50v, which doesn't show up on the schematic provided. That has been bypassed with a 2200uf/100v cap which I'll probably leave. The selenium rectifier has been replaced with a modern diode bridge block, so I'll leave that alone. too. All coupling caps have been replaced with decent quality film caps so I'll leave those alone too.
 
Crestwood23 said:
Very nice! What speakers are you using?
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right now I have them hooked to klipsch kg 3.5. This scott preamp is a lot better than I expected, even in it's current state. I don't find highs and lows to be rolled off at all as some have reported. That filter cap needs to go though.
 
Any idea what the half-round clamp looking thing on the underside next to the transformer is/was for?
 
yeah, this thing is already modified from stock, which is fine, I just don't like that the original multisection filter cap was left in place.
 
drew_t said:
Any idea what the half-round clamp looking thing on the underside next to the transformer is/was for?
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I plan on using that clamp to put the replacement multisection filter cap in, I'm going to use the authenticap 80/40/30/20 with 20 being the first connection after the rectifier so I should still be able to use the 6x4 if I want to. I may replace the 7 pin socket since it's pretty loose. That way I'll be able to get the thing into a case since as is the existing and replacement caps are way too tall to fit in a case.
 
I mistakenly purchased the building manual for the LC-21 a few years back, thinking I was getting the manual for my LT-110 and LK-48. I'll see if I can dig it out and scan it for you.
 
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