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Kt-120 compatibility with Scott LK-150 tube amp

James Cox

James Cox

AK Subscriber
Subscriber
Hey everyone, I'm in the process of picking up a Scott LK-150 but unfortunately it has no tubes. I was wondering if anyone here has tried KT120 tubes on this amp or of they draw too much current to be safely used here. When it gets here this piece is going to need a decent amount of work before it's ready to be put in my system. Other than new caps underneath and restuffing the cans I'll also be replacing the rectifier bridge and the fuse holder. Anyone have any suggestions on where to get the replacement fuse holder?
My other main tube amp is a Citation II so on my first listen I plan on using the kt88 tubes from my citation to make the comparison as fair as possible but after that I'd like to order a new quad for the LK-150.
 
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I am very curious to see if you will like the 150 more than the deuce.
The Citation with kt88's and a tube preamp is pretty darn good sounding.
 
Same here, my preamp I've been using is a brown faced LC-21 so I've been looking for a matching LK-150 OR Citation I to match my citation ii. The LC-21 sounds great with the citation II plus I've fully "Jim Mcshaned" it so it's going to be tough to beat, I'm sure.
 
Ok so I've done a little more research and it seems the big factor to look at here is the difference in heater current needed for the KT120 tube. Looks like they typically draw anywhere from 1.7-1.95A whereas the 6550/kt88 tubes are around 1.65. not a huge difference but when multiplied by all 4 tubes the difference can be as high as 1.2A extra being pulled for a total of 7.8A. Anyone know what the Scott LK-150 output transformers are capable of putting out or know how I could determine that info?
 
its the power transformer, not the output transformer that will care.

Generally I don't expect that most makers over-built their power transformers, so unless you have solid evidence that you have the extra capacity I wouldn't take the chance. Just my 2 cents on it.
 
Don't recommend chancing it. Original iron which isn't knackered is good to have. 1.6 extra amps is significant in terms of most tube amplifiers in terms of filament current over normal operating parameters.
 
My mistake, should've proofread before posting haha
Yeah that's what I was thinking as well, I noticed a good deal for a quad of the kt120s on Bartertown and have always wanted to hear some but don't have any modern stuff that can handle them
 
Any chance you could find room for a 4A 6.3v transformer and feed one channel of output tubes?
 
I bet that a short run of putting KT120's in would not be a problem. Do it on a cool day and don't run it for more than 30 minutes. If it makes a difference to you, then remove some or all of the driver tubes and put them on a separate filament transformer for long-term use. If there is no difference, then you saved yourself the trouble.

I did this exact thing with my Citation II and they sounded no different to me than the KT90s nor did they measure any different.

Using KT120's is only 8 watts more draw on the power transformer. In the case of a Citation II that idles at approx 300 watts you can reduce the voltage via variac by 3 volts down from 120 and you'll get that 8 watts back. Of course the filament windings are still overloaded by 18% or so temporarily but the core isn't.

Another idea is to put KT120s in one channel only then you reduce the overload by half and can do a 1:1 comparison. Or do a mono comparison running KT120s in one channel and no tubes in the other.
 
nerdorama said:
Any chance you could find room for a 4A 6.3v transformer and feed one channel of output tubes?
Click to expand...
That's an idea but I'd like to avoid any serious mods if I can. I guess if I add the filament transformer I could still use 6550 and kt88 tubes right?
 
rustnrot said:
I bet that a short run of putting KT120's in would not be a problem. Do it on a cool day and don't run it for more than 30 minutes. If it makes a difference to you, then remove some or all of the driver tubes and put them on a separate filament transformer for long-term use. If there is no difference, then you saved yourself the trouble.

I did this exact thing with my Citation II and they sounded no different to me than the KT90s nor did they measure any different.

Using KT120's is only 8 watts more draw on the power transformer. In the case of a Citation II that idles at approx 300 watts you can reduce the voltage via variac by 3 volts down from 120 and you'll get that 8 watts back. Of course the filament windings are still overloaded by 18% or so temporarily but the core isn't.

Another idea is to put KT120s in one channel only then you reduce the overload by half and can do a 1:1 comparison. Or do a mono comparison running KT120s in one channel and no tubes in the other.
Click to expand...

That's a good idea to try first, that way I could decide if it's worth the extra effort
 
James Cox said:
Hey everyone, I'm in the process of picking up a Scott LK-150 but unfortunately it has no tubes. I was wondering if anyone here has tried KT120 tubes on this amp or of they draw too much current to be safely used here. When it gets here this piece is going to need a decent amount of work before it's ready to be put in my system. Other than new caps underneath and restuffing the cans I'll also be replacing the rectifier bridge and the fuse holder. Anyone have any suggestions on where to get the replacement fuse holder?
My other main tube amp is a Citation II so on my first listen I plan on using the kt88 tubes from my citation to make the comparison as fair as possible but after that I'd like to order a new quad for the LK-150.
Click to expand...
Why depart from KT-88 ? It's a more linear tube and it's possible to get without supporting putin's gang.
There is no technical reason, and KT120 is much more unlinear.
 
The grass is always greener as they say haha. Not so much about it being a better tube but more about trying something different.
 
Starting my restoration on this piece soon. Getting parts and stuff in order now. Do you guys think I should do a full restoration thread on it since there aren't many in here already? Transformers are pretty banged up so going to repaint those. Thinking about trying to match them to my Chocolate face LC-21 but may just go with the original black if I can't find something close enough.
Also going to need a full recap. Haven't decided if I'm going to restuff the cans myself or just order some hayseed caps. Goin with K40s on the coupling caps for sure. Does anyone know what value bridge rectifier I need to replace the original selenium one? I usually use a 4a 400v for the other Scott integrated amps Ive restored but this is my first time with an LK-150 and want to make sure I get it right the first time.
 
My vote is at any level of restoration (full or partial) would be very much appreciated for posting. I don't own a Scott LK-150. But I enjoy seeing restoration shared on AK. Regards.
 
Right on, i think I'll take some nice pics tomorrow and start a fresh thread. I'll be doing it in my leisure time so probably be 3-4 weeks of me working on it before I'm done
 
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