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Scott LK-150 restoration thread

After scouring the internet I've finally found a picture of one that ahs had the service bulletin performed and I'm pleased to say I was right. Looks like I just have to add the 6.8k ohm resistor and bypass the resistors on the bias pots and I should be good to go! Here's the pic in case anyone is curious. In the pic you can see the 2 resistors combined to make 6.8k connected from pin 2 c1 to pin 5 (ground lug) c1. Only a few more hours of work left guys, then this thing will be singing again!!Screenshot_20221109-140407.png
 
So hayseed is pretty backed up I guess so I'm still waiting on can caps but figured I'd go ahead and update with what I've got done so far. I went ahead and changed out all of the resistors that are over 1/2w except for 2. Probably not necessary but I had most of them on hand anyway so figured why not. I couldn't find a 1.2k/10w resistor and I missed the 220ohm since it wasn't on the parts list I was working with. Both measure pretty much dead on so I'm not going to sweat it. Once the can caps get here I'll change the 10ohm resistor and ad the 6.8k resistor and everything will be done!
 
James Cox said:
So hayseed is pretty backed up I guess so I'm still waiting on can caps but figured I'd go ahead and update with what I've got done so far. I went ahead and changed out all of the resistors that are over 1/2w except for 2. Probably not necessary but I had most of them on hand anyway so figured why not. I couldn't find a 1.2k/10w resistor and I missed the 220ohm since it wasn't on the parts list I was working with. Both measure pretty much dead on so I'm not going to sweat it. Once the can caps get here I'll change the 10ohm resistor and ad the 6.8k resistor and everything will be done!
Click to expand...

Hayseed can take a little time to deliver, but it is well worth the wait.
 
I checked most of the 1/2w resistors in circuit. I know that won't give a super accurate reading so I just compared left and right channel to make sure they were close. Everything looked good so I'm not going to mess with those yet. Maybe change them out in the future if I notice the amp being extra noisy or something.
And I agree Pete, hayseed cans are definitely the best in the market and worth the extra cost and wait if your restoring a nice piece!
 
The cans finally made it in and I had enough time to swap them out between customers today. Unfortunately I forgot to bring the power tubes from my citation at home to test it with so won't know how it sounds until I come back in on Tuesday. I'll update here when do some testing on Tuesday and let everyone know how it goes!
 
So I scored a set of early Svetlana "Winged C" 6550c's. The date codes look to be from 97. No winged C label on the tubes but I guess the first few years weren't actually labeled as winged c's even though they are the exact same tube. I have a pair of vintage Mullard rectifiers coming tomorrow and will finally be able to get this thing up and running. On a side note, does anyone know where I could get a metal ring manufactured for my power knob? The other knob has the ring and I could send that off to be copied if that's a possibility
 
Someone with a metal lathe and the skills could probably make the ring fairly quickly.

Before you fire up with the new tubes there are strategies you can use to minimize things like what happened last time you powered it up. I use a variac to limit the amount of wall voltage.

Check the HT at the rectifier tubes, without tubes and if the AC voltage on pins 4 and 6 looks ok try it with only the rectifier tubes.
Bring voltage up slowly and at some point the tubes will conduct and you can verify that it’s making DC voltage as it should.

Monitor current as you do this, or use in tandem with a dim bulb tester. If you made any wiring mistakes with the filter caps this is where you can catch it before there is damage.

If all looks good check for the presence of negative voltage on the power tube socket grid pin 5. Check all four sockets and this is without power tubes installed. If the voltage is adjustable, adjust it to the most negative voltage (farthest from ground).

There may be a few more startup tips but the ones I mentioned are specific to the work you did and honestly, they can be done in short order.

Gradual and methodical are the keys.
 
Those are some great tips! I usually fire it up with my dim bulb tester first and if there's no shorts present I'll dial the bias all the way down and set that before applying a signal. Gradual and methodical is definitely how I work, one component at a time, but once I get down to brass tacks and it's ready for testing I catch myself skipping the voltage checks because I'm too antsy to see how it sounds Honestly I just got too excited on this last one and skipped the dbt all together. There was no smoke or anything like that so I think I'm good and I still get the correct readings on the transformers. My rectifiers where delayed in the mail so gonna have to wait a few more days. I think I should get in the habit of checking voltages against a schematic BEFORE playing music though. Probably could have avoided extra work in the past.

And on a side note, I believe I purchased my Sansui 1000a from you a few years ago. I came to your house and we jammed American Beauty and you showed me some of your dead tapes collection. How've you been man? You'll be happy to hear the Sansui is still going strong. I ended up giving it to a really good friend of mine for his 50th birthday along with a dual 1218 I restored, a set of realistic speakers, and a crate of albums from my shop. He works from home and says that he plays it at least 6 or 7 hrs a day and has even forgot to turn it off overnight a few times and has never had a single issue with it!
 
Hey, yep, I remember it well. I’m doing fine, thanks. Been messing with turntables more than tube amps lately. It’s good to hear about the ‘Sui, that was a great gift and I am glad its getting played.

Sounds like you have a good process for startup; I could tell you were a bit anxious last time so that’s why I chimed in.
Let us know how it goes. Play Box of Rain!
 
Alright got some strange readings and decided to double check my work against the schematic. Everything looked good until i got to the diode. The original has the polarity marked backwards compared to how I'm used to reading diodes. On the schematic they have the cathode marked as positive and the anode marked as negative. Goin to grab some lunch and flip this diode around when I get back and see if my readings make more sense. Wish me luck!
 
Yup, the diode needed to be reversed. So for anyone reading this in the future the polarity markings on the selenium diode are reversed from a modern silicon diode. It holding bias and sounds sweet but there is a pretty significant channel imbalance. Would weak 7199 tubes cause that problem? I'm still waiting on new ones but pulled this marginal ones from my stash to use for now. They are pretty closely matched to each other butnon the weak side. Other than that there's only a handful of resistors I haven't replaced so guess that's where I'll start digging
 
Nevermind, I'm a dingus haha. Somehow I had the negative speaker connection hooked to the 4 ohm tap instead of the ground tap on one of the channels. Fixed that and now it sounds perfect! Thanks for everyone's help! Going to get this thing hooked up in my main system at home and report back in a few days with my final judgements on this one
 
Nice work diagnosing the diode problem ….. and the speaker connection. Glad to hear that it is singing; it’s a great feeling when your work comes to fruition.

What preamp etc are you using with it?
 
So for the initial testing I just hooked up my mp3 player directly to the amp since the mp3 player has a volume control. Now that I have it home I'll be taking my citation ii off the rack and connecting this to my Scot LC-21 preamp. Once I work up the strength on plan on moving my altec 19s from the shop to my main system at the house with the lk-150/ lc-21 combo.
 
Late to this thread but look up farmediacom

Daev restored some HHScott amps incl lk150 and has technical info posted.
 
Finally got everything hooked up and had time for a couple records this morning while making breakfast. Gonna sit down for some more serious listening this evening and I'll post my initial comparison of the LK-150 vs my citation II
 
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