New HH Scott LK-48 In The House - Restoration Ahead

[njcanuck]

Sometimes I just can't resist! Found this very nice condition HH Scott LK-48 for a reasonable price.
I checked the tubes and powered it up carefully on the variac and it works! Nice sound from both channels although the pots are a little scratchy. No hum at all. Not bad for an almost 60 year old amp! A good cleaning and a full restoration and she'll be like new again. Might try adding in Dave Gillespie's EFB circuit on this one - I sure like the way it works on a couple of my other amps. Time to start putting together the parts list.

 

[Blast]

Very nice! It should respond nicely after some love.

 

[Dave451]

Nice amps! Really like the dark front look. Watch those old can caps and for sure replace the Siemens selenium bridge rectifier in the bias/12AX7 filament DC supply.

 

[njcanuck]

Nice amps! Really like the dark front look. Watch those old can caps and for sure replace the Siemens selenium bridge rectifier in the bias/12AX7 filament DC supply.

Yup, new can caps, coupling caps, grid resistors, bias rectifier, bias controls and test jacks, plus a few other components that I haven’t remembered yet. I’ve restored several Scotts over the years. The workmanship looks very good for a kit. The only previous work appears to be a new volume / loudness pot.

 

[Dave451]

Mine was well-built as well, but I actually did find a couple of unsoldered joints in it. Interestingly, it had a precision audio pot installed for volume control and, since the on/off switch went with the old pot, re-purposed the Loudness switch to on/off duty. Sounded great.

Trying to figure out what "THIS ONE" written on top means?

 

[njcanuck]

Mine was well-built as well, but I actually did find a couple of unsoldered joints in it. Interestingly, it had a precision audio pot installed for volume control and, since the on/off switch went with the old pot, re-purposed the Loudness switch to on/off duty. Sounded great.

Trying to figure out what "THIS ONE" written on top means?

Since new volume pots with loudness connections are very hard to find, they are often replaced without the loudness function. This naturally frees up that switch for on/off duties. I actually wired a previous LK-48B that way. Never should have sold that one - think I’ll be keeping this one.

“THIS ONE” points to the power / volume switch. I think it was directions for the rest of the family.

 

[Dave451]

Exactly! Goof Off or the like will take that off, if you're confident you'll remember what "This One" is! (LOL)

The Scott 222 series amps have a lot to recommend them, and I could easily see this one being a prized keeper. It appears to be in quite good physical condition, particularly the front plate, and the sound will speak for itself. Good luck with it!

 

[Dandy]

Nice find NJ. Don't recap the tone section unless the Ceracaps there are definitely bad.

 

[njcanuck]

Pondering caps for the power supply rebuild. Currently there are six 20uF / 450V caps separated by resistors . I am going to replace them with JJ 500V caps. Originally I was planning to go with the 32uF’s but the 50uF’s are also an option.

Are there any downsides to upping the capacitance to the 50s? Spec says the 5AR4 rectifier can handle it but I am wondering about other downstream components.

 

[nj pheonix]

Happy to see you Rich,
I was thinking I haven't seen you in a while and I thought maybe something happened to you.

 

[nj pheonix]

As long as the first cap is under 60, you should be good to go
For sake of tolerance I think I'd maybe use a 47uf for the first cap off the rectifier.
You can bump the others over stock but there's little gain to going overboard. Maybe 20%

 

[njcanuck]

Happy to see you Rich,
I was thinking I haven't seen you in a while and I thought maybe something happened to you.

Hi Andy, been out fishing! It’s what we do down here. I’ve also been drooling over your Mac 225.
Good to hear from you again.

 

[Blast]

Pondering caps for the power supply rebuild.

I used a couple of JJ 40-20-20-20 in my 222C:

 

[nj pheonix]

Big iron for a EL84 amp



For reference
Eico 2036

 

[njcanuck]

Yeah, both this LK-48 and the previous LK-48B that I had have huge outputs. These amps really have balls in the bass department.

Just finished reading that too much capacitance can lead to arcing in the output tubes. Think I’ll stick with 32uF throughout the power section.

 

[Blast]

32... 33...

 

[Dandy]

While it's in the shop, consider adding the 222D bias circuit too.

 

[Blast]

While it's in the shop, consider adding the 222D bias circuit too.

Good call!

 

[njcanuck]

I had to lookup the 222D schematic. It appears to be the same bias setup as the 233 that I usually use.

 

[Bradbrews]

If you do add the bias circuit from the 222D, please post some pictures of how you do it.
I've been thinking about doing that to my KL-72, but so far have just been listening to it and enjoying!