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Scott LK-150 rebuild/modification thread

I think this should have everything fixed. Re-drew a couple of connections for clarity, removed a duplicated capacitor, and fixed the MOSFET. It was drawn in backwards in the early versions.

 
Not many great ways to do that without punching holes in the chassis for more sockets.

Also, I happen to have a nice supply of 7199s, 6U8As and 6GH8As around. :)


s-petersen said:
Updates?
Click to expand...

Got the chassis completely stripped and scrubbed, opened up the octal socket holes a bit more for mil-spec ceramic sockets from the 1950s (not the most perfect job, admittedly, but they'd already been messed with in the past), and got the new ceramic octal and nine-pin sockets installed, along with the front-panel slider switches. Still need to drill holes on the top for the new bias pots and open up the terminal strip holes for the new collection of binding posts.
 
Still deciding exactly how to orient the caps. Soliciting opinions for both cosmetic and functional purposes.

Option 1:


Option 2:


Option 3:


Kinda leaning towards #1. #2 would give the 5AR4s a bit more ventilation room. I'm not too keen on turning the capacitor lettering outward. Option #4, not pictured, would be a combination of #2 and #3.

Considering that I'm working with mostly new parts, and I stripped everything that was still riveted off of the chassis, I decided to switch to the modern "red=right" convention and flip-flop the red and black switches. I got lucky and just happened to find that red Switchcraft switch, the exact one that Scott used when this amp was new, on eBay. Someone had just listed a bunch for sale when I happened to look, and they sold fast.

There are a couple of places where something stripped the gold anodization by the V8 socket. I'll deal with that later. I'm also going to fix the mess the previous lunatic made of the front panel where the logo was.

Considering that I only have one of the original knobs, and Scott only used that particular, large knob on the LK-150, I'm thinking about replacing the original rotary power switch with something like one of these:
http://www.radioshack.com/spst-lighted-rocker-switch/2750692.html
http://www.radioshack.com/spst-16a-125v-illuminated-round-rocker-switch-with-red-led/2750020.html
http://www.radioshack.com/spst-rocker-switch-red/2750694.html
http://www.radioshack.com/spst-heavy-duty-rocker-switch/2750690.html
http://www.radioshack.com/dpdt-heavy-duty-rocker-switch/2750691.html
 
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Sam,

Put up a picture of the Knob you have I might have a match on hand.

I see Dave has been up to his handy work on this! I did a ST35 with the EFB for a customer not long ago. It really does work well for that amp. I'll find it surprising if much is to be had doing it with this amp though. Just making it where you can bias the output tubes separately would have netted you about 99% of what EFB will do from a real world listening stand point. In fact in stock form the amp is already 98% there if nicely matched pairs of output tubes are used IMHO...

But what the heck as long as your having fun!
 
this has been a great thread so far...My LK-150 will be here soon,will likely listen to it for a week or so as its operationable and had been recapped in the past.
Then it will be going in to my buddy for full recap,

hunter
 
NOSValves said:
Just making it where you can bias the output tubes separately would have netted you about 99% of what EFB will do from a real world listening stand point.
Click to expand...

Don't underestimate what the source-follower screen reg will do for the output tubes. It is *NOT* a small improvement. The 6CB5A amps I had at the last 'Fest were rigged that way...:) Not a triode to be seen in those amps.
cheers,
Douglas
 
NOSValves said:
What brand are those filter cans? I think that gold screen print looks great in option 3
Click to expand...

Angela Instruments, glued to some NOS fiber twist-lock bases that I picked up on eBay (the little can has an extra fiber washer under it so that it would actually cover the holes in the base). Battradio turned me on to them after one of my Fisher 70s blew a cheap filter can from AES at one of Sheltie Dave's gatherings, when it had maybe 20 hours of run time on it. As long as I can get away with two-section cans, they're pretty much my go-to now. The performance is very good, and the price is unbeatable.

http://www.angela.com/electrolyticcapacitors.aspx

The two big ones are a 100uf/100uf 500V and a 50uf/50uF 500V, the smaller two are a 32uF/32uF 500V and an 8uF/8uF 500V that will be paralleled to make the two 40uF caps for the bias side of the power supply.

NOSValves said:
Sam,

Put up a picture of the Knob you have I might have a match on hand.

I see Dave has been up to his handy work on this! I did a ST35 with the EFB for a customer not long ago. It really does work well for that amp. I'll find it surprising if much is to be had doing it with this amp though. Just making it where you can bias the output tubes separately would have netted you about 99% of what EFB will do from a real world listening stand point. In fact in stock form the amp is already 98% there if nicely matched pairs of output tubes are used IMHO...

But what the heck as long as your having fun!
Click to expand...

This is going to have individual output tube bias as well. I borrowed that section of the schematic from the Citation II, with some values tweaked to bring the resistances back around to what Scott specified in their rather more complex setup.

Here is the knob, on the right, next to a standard Scott LK-series knob:

As far as I can tell, the only thing they used it on was the LK-150, and it wasn't an off-the-shelf part from a supplier. It's bigger than the "standard" knob, both in diameter and thickness, the sides are straighter and fluted, and the center is flat instead of cone-shaped.
 
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PakProtector said:
Don't underestimate what the source-follower screen reg will do for the output tubes. It is *NOT* a small improvement. The 6CB5A amps I had at the last 'Fest were rigged that way...:) Not a triode to be seen in those amps.
cheers,
Douglas
Click to expand...


Trust me Pak I'm not underestimating anything....You should follow your wild exaggerations with IMHO.... that is IMHO
 
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Sam Cogley said:
Angela Instruments, glued to some NOS fiber twist-lock bases that I picked up on eBay (the little can has an extra fiber washer under it so that it would actually cover the holes in the base). Battradio turned me on to them after one of my Fisher 70s blew a cheap filter can from AES at one of Sheltie Dave's gatherings, when it had maybe 20 hours of run time on it. As long as I can get away with two-section cans, they're pretty much my go-to now. The performance is very good, and the price is unbeatable.

http://www.angela.com/electrolyticcapacitors.aspx

The two big ones are a 100uf/100uf 500V and a 50uf/50uF 500V, the smaller two are a 32uF/32uF 500V and an 8uF/8uF 500V that will be paralleled to make the two 40uF caps for the bias side of the power supply.



This is going to have individual output tube bias as well. I borrowed that section of the schematic from the Citation II, with some values tweaked to bring the resistances back around to what Scott specified in their rather more complex setup.

Here is the knob, on the right, next to a standard Scott LK-series knob:

As far as I can tell, the only thing they used it on was the LK-150, and it wasn't an off-the-shelf part from a supplier. It's bigger than the "standard" knob, both in diameter and thickness, the sides are straighter and fluted, and the center is flat instead of cone-shaped.
Click to expand...

Actually they used both those styles during the production of the LK-150. But with both styles they were always that large. I personally think the amps look better with a smaller all gold anodized aluminum knobs like the earlier power amplifier came with. I have some of those also. I'll have to dig through my stash and see if I have one to match the style you have. Give me a few days I'm buried with work around here. If I have one its yours for the cost of priority small box flat rate. If you don't hear from me by the end of next week rattle my cage via PM.
 
The LK-150s I've seen for sale have all had the fluted knobs.

Just looked at the back of both knobs - made in Japan. Huh. Would not have guessed that.

I figured the Angela caps were probably Chinese, but they seem to work well. Unlike the cheap AES cans... :no:
 
Sam Cogley said:
The LK-150s I've seen for sale have all had the fluted knobs.

Just looked at the back of both knobs - made in Japan. Huh. Would not have guessed that.

I figured the Angela caps were probably Chinese, but they seem to work well. Unlike the cheap AES cans... :no:
Click to expand...


Oh don't read anything into my Tiawan/Chinese comment those cans are decent. I don't see a 50/50uF @ 500V on Angela's website. Geezzzz I haven't been there in years. I used to buy a good bit of parts from them 10 to 12 years ago before I started buying most everything direct from the manufacturers.

I bought about 40 of the 32/32uF @ 500V Ruby Gold's directly from Ruby a few years ago and tried them out, I thought they were darn nice and my cap analyzer showed they did a nice job all around. At the time the 50/50uF they sold was too tall for the Scott integrated amps to still get a factory case on it by about a 1/4" so I complained but they never did anything about it at the time. What is the height of that 50/50uF you have?

Heck I even cut these things apart to investigate the quality....the Ruby and JJ are very similar inside....the AES cheapo not so much ;)

I never noticed the Japan markings....interesting. But really not that surprising the fluted Marshal style Scott knobs they used were made in Germany. All the vintage manufacturers were very much global shoppers...heck they almost exclusively used imported tubes.
 
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