Hi all,
Looking at a Scott LK-48 for sale and wondering how much work has or needs to be done. Anyone know?
Looking at a Scott LK-48 for sale and wondering how much work has or needs to be done. Anyone know?
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All the electrolytic and paper coupling capacitors should be replaced.
The tubes should be checked, and all contacts and controls should be cleaned.
Resistors are carbon comp, and should be checked for being within tolerance.
That said, it might actually work ok as-is, it looks pretty good. How much are they asking?
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Probably replace all those 0.1uF coupling caps with decent film types, as the paper caps often go leaky and screw up the bias.
If there is a selenium rectifier in the bias supply, replace it with a silicon bridge and re-tweak the bias
Either re-form the HV electrolytics (if they still have any life left), else replace them with fresh multi-section cans (pricey and a PITA). Another dodge would be to leave the old cans in place, trace out the connections one by one, cut each and add caps below decks to take over the duty, leaving the old cans in place for cosmetics. Better electrolytic caps are made these days, and the caps can be placed exactly where they need to be.
The unit looks really clean....
If there is a selenium rectifier in the bias supply, replace it with a silicon bridge and re-tweak the bias
Either re-form the HV electrolytics (if they still have any life left), else replace them with fresh multi-section cans (pricey and a PITA). Another dodge would be to leave the old cans in place, trace out the connections one by one, cut each and add caps below decks to take over the duty, leaving the old cans in place for cosmetics. Better electrolytic caps are made these days, and the caps can be placed exactly where they need to be.
The unit looks really clean....
Thanks wrenchone. I'm a newbie and was hopeful that this unit would have some or all of the necessary mods done but couldn't tell looking at the photo. It does look clean and supposedly works once it gets tubes (has none) but I'd be concerned about running it without the upgrades you discuss and am not sure I want to spend the $500+ to have someone else do it! With shipping it's $500 as is....
The unit looks stock, with no upgrades. The coupling caps are the old wax paper things one used to see in 50s/early 60s TVs and HiFi stuff, though a step above bargain basement.
Yeah I hate to admit it but....you're right. If I could do the upgrades myself I'd take it on....🙁
The coupling caps maybe ok. They are not wax caps but ceramic tubes with epoxy or something like that end seals. I have found that they are sometimes good depending on how much use or abuse the amp received. The LK48 is a very good sounding amp and you might kick yourself in the .... if you pass it up and regret not buying it. Scott amps are very well made and sometimes even after all these years they are running perfectly. It is usually the ones that look nearly mint that are like that.
For what it's worth, I wouldn't pay $500. More like $350, maybe 400 (What I think it's worth, I wouldn't buy one period because of all the trouble to go through and I'm not fond of the "shiny" look) But, again for what it's worth, the transformers in here are amazing. The power transformer is adequate, and the output transformers...Well, i had one a while back and built an amp using just the PT and OPT's from the Scott. A 6bg6ga push pull, with 6SN7 CCS LTP driver. It was probably the most transparent and silky smooth amp I have built to date. Nothings perfect, but the mids/highs from that amp were damn close.
You risk any or all the transformers and maybe output tubes if you don't recap it fully (PS including can caps & coupling caps).
Coupling caps are very low cost even for good ones and can caps can be left in place for looks (unhooked)and for much lower cost individual caps can be wired in under the chassis. Some people buy skinny caps and re stuff the cans also.
Not hard on those as at least there is room. Just take lots of pics with lots of detail first. One cap at a time so no mix ups and then test. You can use the old leads to solder the new caps to.
Always have speakers hooked up when testing or you can ruin output transformers and tubes don't like short cycling ( let cool off well before restarting) .
If it's $500 CDN maybe not bad when you consider what $300-350 US will cost shipped and exchange!
Coupling caps are very low cost even for good ones and can caps can be left in place for looks (unhooked)and for much lower cost individual caps can be wired in under the chassis. Some people buy skinny caps and re stuff the cans also.
Not hard on those as at least there is room. Just take lots of pics with lots of detail first. One cap at a time so no mix ups and then test. You can use the old leads to solder the new caps to.
Always have speakers hooked up when testing or you can ruin output transformers and tubes don't like short cycling ( let cool off well before restarting) .
If it's $500 CDN maybe not bad when you consider what $300-350 US will cost shipped and exchange!
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Actually they're not - they are American Radionics film caps in ceramic bodies, regardless they need to be replaced because due to thermal cycling (Scott amps get hot!) they tend to become intermittent or open up altogether. A shame really as they are otherwise pretty decent performers.
Depending on the number of hours on this unit the can electrolytics might be OK if properly reformed, but probably better to not make the assumption.
$500 seems pricey to me, but Scott gear these days does command a pretty hefty premium if it's in great shape. This one looks very good.
Note that the bias/filament filter cap is common POSITIVE, a normal can will NOT work here.
http://www.vintagevacuumaudio.com/schematics-manuals/hh-scott/hh-scott-lk48-b-schematics.pdf
Note also that this was a kit amp. This one appears to have been assembled very competently, but that is not always the case.
$500 seems pricey to me, but Scott gear these days does command a pretty hefty premium if it's in great shape. This one looks very good.
Note that the bias/filament filter cap is common POSITIVE, a normal can will NOT work here.
http://www.vintagevacuumaudio.com/schematics-manuals/hh-scott/hh-scott-lk48-b-schematics.pdf
Note also that this was a kit amp. This one appears to have been assembled very competently, but that is not always the case.
I had an LK-48... 25 years ago. Time does fly, doesn't it.
And yes, those ceramic coupling caps were stock with the unit. The first thing I did - back then - was to replace those with some Wondercaps (remember those?!) and some Wimas. It was an improvement - weird thing is the new coupling caps seemed "louder" - ie, the volume control was more sensitive and I didn't have to turn it up as much to get to my preferred listening level. I never figured that one out.
Those, and the electrolytics - including the big can cap - should be replaced.
The carbon comps will also be out of spec... not such a big deal for some positions in the circuit. Replacing the resistors, however, will be a painful exercise.
And yes, those ceramic coupling caps were stock with the unit. The first thing I did - back then - was to replace those with some Wondercaps (remember those?!) and some Wimas. It was an improvement - weird thing is the new coupling caps seemed "louder" - ie, the volume control was more sensitive and I didn't have to turn it up as much to get to my preferred listening level. I never figured that one out.
Those, and the electrolytics - including the big can cap - should be replaced.
The carbon comps will also be out of spec... not such a big deal for some positions in the circuit. Replacing the resistors, however, will be a painful exercise.
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