KT120/150 SE UL Build

[srb02]

A new build is up and running.
History behind it: I had built Kegger's KT88 SE UL (6EJ7 version) several years ago. I asked for a pair of KT120's for Xmas 2 years ago, and Santa obliged. They dropped right in and wow, they took this amp to a new level, but it wasn't optimized for the bigger tubes, nor did it have big OPT's.
10 months ago, I decided to do an all-out build for the KT120 tubes.

And here we are: 50 pounds of the most awesome sounding amplifier I've ever had the pleasure of listening to.
Yup, it's downfall is weight. Transformers and chokes alone are 40 lbs. All motor run caps in the power supply, CXSE25-5K 25 watt OPT's, 400-0-400 325Ma Power transformer, B+ = 475.

Kegger helped tweak the layout, designed the power supply, and setup the schematic to get these big tubes to sound their best. This thing just sings. Smooth, powerful, big tight hard bass, the mids are full, real full, and the highs, just unbelievably pretty. Its incredible, transparent really, and sound stage.....WOW.

Your wondering: he's keeps talking about KT120, but it has 150's in. Yup, one of the later conversations the comment was made: If the 120's sound this good, what would the KT150's sound like? And a pair showed up within 7 days... They are "as good as" the 120's. Time will tell, we're letting them burn in, and get some hours, and there might need to be a few tweaks, maybe not.
Tubes: 2-KT150, 2-6EJ7, 2-5AR4 rectifiers.

My two cents Stu

 

[Brice]

Awesome !! In all counts. Love the film caps tucked in under the hood and heat shielded.
Beautiful design and execution.

Wish I could hear it

 

[sKiZo]

Have a chance to measure the power output of that bad boy? I'd expect some drop in a UL build, but then again, you've got a LOT of potential to work with.

Love the KT120's just doing what you did, dropping them into a KT88 amp. Very strong and tight on the bottom, and clean power all the way to the top. Also very competitively priced compared to most decent KT88's. Word of warning to any readers ... DO make sure your iron can handle the extra demand these tubes will demand!

 

[RUmad]

Absolutely love it

 

[srb02]

Thanks for the comments guys. and no Skizo, we haven't measured it yet, still burning in.
The plan was for 14 watts or so, w/ the 120's, so now w/ the 150's 17 watts, maybe. I don't plan on pushing these things to their limits.
Now it's a "tweak" in progress. Bypass caps and other minor things to try.

 

[Don P]

i want one.lol nice
Don

 

[kward]

The KT120 is a really good sounding tube, IMO. But you won't get any additional output power with the 150's unless you increase B+ voltage or change bias.

What brand of 6EJ7 are you running?

 

[srb02]

Yes, with the current setup I feel the 120's are really happy there. As they do sound really, really nice. Still a bit nicer than the 150's. Maybe that's because the 150's son't have a lot of time on them.

6EJ7: Kegger recommended Mullards screen plates, and low and behold, I had a pair in a bag of tubes I got at a yard sale.
So currently Mullards and Black plate Sylvania's w/ yellow lettering are my 1's.
Sylvania black plates w/ green lettering seem a bit dark, but still nice -- #2,
GE solid grey plates are nice (usually cheap) #3, the Russian ones (don't remember #'s) are not bad --#4, everything else Zenith--yuck, #5 and lower.

My two cents Stu

 

[NOSValves]

I suspect you have an error on the schematic. I wouldn't think you would feed the plate of the driver tube via the winding of the output transformer.

 

[Kegger]

Actually he has it correct,

The plate voltage is being fed from the power supply, then 2 75k plate resistors in parallel.
But also 150k feedback resistor from the plate of the output to the plate of the driver as well.

 

[NOSValves]

Ahh okay I see. It was kind of drawn funny. When I seen the 150K 2 watt I just assumed it was the plate resistor.

 

[Kegger]

Yah I had to look at it a little harder to..

 

[drtool]

Great job. Love it. SE 120 kudos. My maggie was the first SE I have tried. Now I can't get enough of tubes.

 

[primosounds]

Nice amp! I was wondering why you decided on 5K for the primary of the output trans. From what i have read for KT88 most builders use 3 or 3.5K primary impedance for the OPT. Also is this schematic one of your own design? cheers.

 

[srb02]

thank you. I wished I had the skills to design one of these amps. But that's not going to happen any time soon.
No, I get the enjoyment out of reading a schematic, acquiring all the parts and pieces, than building it and listening to the wonderful music. Still plenty of enjoyment.
This is one of Kegger's designs. He has provided the technical expertise and advice, for which I am most grateful.
My two cents, Stu

 

[Kegger]

As to the primary impedance, it's a choice/trade-off.
Anything from say oh 3-6k will work in this type setup.

The lower the primary: The higher the power, higher the distortion, and less linear.
With it being the opposite on everything as you go the other an Increase the primary.

5K is where I've settled to my needs/wants for the overall outcome..

 

[Tucker99]

Very nice.
PMing the OP with with an off thread question.

 

[djnagle]

nice build. I like to build an amp with the 150 just because it looks so cool.

 

[Tubeglowpio]

Yes, with the current setup I feel the 120's are really happy there. As they do sound really, really nice. Still a bit nicer than the 150's. Maybe that's because the 150's son't have a lot of time on them.

6EJ7: Kegger recommended Mullards screen plates, and low and behold, I had a pair in a bag of tubes I got at a yard sale.
So currently Mullards and Black plate Sylvania's w/ yellow lettering are my 1's.
Sylvania black plates w/ green lettering seem a bit dark, but still nice -- #2,
GE solid grey plates are nice (usually cheap) #3, the Russian ones (don't remember #'s) are not bad --#4, everything else Zenith--yuck, #5 and lower.

My two cents Stu

I am planning a build around keggers kt-88 but using kt-120 with higher voltage and more current, how much better does this sound then the kt-88 amp? and was the 6EJ7 chosen because the 120's needed more to drive them?

 

[sKiZo]

Haven't been able to determine from the pics whether the socket mounts are drilled all the way thru for ventilation? If so, nice touch - my tubes run a LOT cooler due to chimney effect by being able to draw cool air from under the chassis plate ...