DIY Audio Projects Forum

Old thread but then I'm an old guy.

I've just tried out the KT120 in my Mikael Abdellah Single-Ended (SE) KT88 Tube Amplifier:

http://diyaudioprojects.com/Schematics/ ... lifier.htm

400V, GZ34, Angela Universal PT, James 6123 OPT@ 5k. 560 Rk per tube. This PT is underpowered for the KT120, Not enough filament or HT current. Oh dear......And the OPT Max idle is 100Ma where the KT120 wants about 165mA. So my amp is underpowered for the KT120.

Here are my thoughts.....

I was not happy with the sound with EL34 in triode or UL. Too thin to my old ears. Or maybe not enough power? My speakers are 99dB/W/m Goodmans Axiom 201 16 ohm full range in factory cabinets. This may be part of my harshness problem. But there is something entrancing about a full range driver that I like......

The amp sounded smoother and fuller when I doubled the current through the 6N1P.

Then I tried KT88. This was a great improvement for bass and top end smoothness. But still harsh vocals in UL. I prefer both EL34 and KT88 in triode mode in this amp. But still, a disappointing sound for my first SE tube amp

I've just tried some KT120's with no circuit changes. That's a cold bias and high OPT impedance for this tube, I know.

But the results are quite promising IMHO.

At these less than ideal operating points, triode mode sounds quite nice. It feels like there's less power than the KT88's (?) but there appears to be more headroom. I had always assumed that the CD player was overloading the 6N1P but it seems maybe it was the OP tube that was getting overdriven. With the KT120's I can wind the input pot up to full whereas with the KT88's and EL34's I could only get half way on the pot before the distortion got too objectionable. I guess this is because I am significantly under-driving the KT120's.

UL sounds a lot less objectionable with the KT120 than with the KT88 (or EL34). But it's by no means perfect. The top end harshness I have come to associate with UL is still there but not nearly so prominent. The congested midrange is still there too. But the bass improvement is (almost) worth it. I have read that this tube works well in UL and I believe it. This could be a significant advantage with this tube.

My better half likes the increased bass, bless her.

My next move will be to increase the anode current to about 100mA (max idle current for the James 6123).
This will still significantly under-drive the KT120's however.

And I plan to try the 3.5K UL option on the OPT.

I like these tubes. They sound quite promising even running under these less than ideal conditions.

The KT120s run great in push-pull class A U/L. roughly 45 watts RMS and all the bass you could ask for. I just hope they don't screw them up in future production runs.

EDIT: Just posted to the site are my schematics for such mono blocks and here is a link to a review of the assembled commercial version: http://www.analogplanet.com/content/vc- ... lifier-kit

Good listening
Bruce

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Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

I built a bread board amp with the KT120 and thought it fine. But I recently built two EL34s with 6n1P driver like yourself and absolutely loved them. I did have some excellent NOS Svetlanas that I'm sure ensured the perfect sound. I ran both in UL mode and both sold far too quickly.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic

Wow, that is just what I wanted to hear.

Thanks for the fast and interesting responses.

I must have a look around for some NOS EL34's. I think from what I've read here, maybe I should run more current through the output tubes?

I've been wanting to try a PP amp for some time now and, thanks again to what I've been reading here (did I mention this is a great forum?), it sounds like KT120's will suit me nicely.

I only got to hear my new KT120's in SE U/L for about a 1/2 hour yesterday.
Today, I turned the volume up full, sat down in front of the speakers and clicked play on the CD remote.

I almost had a heart attack! I had no idea it was going to be so loud. It's a huge power increase over the KT88. It's like the whole amp has been supercharged! Today, I prefer U/L over triode mode. It's great having both with the KT120 in SE at least.

In the meantime, though, the KT88's are out and the soldering iron is warming up.

I'll be using the Supercharged SE U/L until I get the class A PP U/L built. Then I will convert it back to EL34 for some tube rolling. Thank-you so much for being so generous with all your research, gentlemen.

I love the smell of flux in the afternoon.

I was listening to a Consonance KT88 integrated amp tonight, 100Wpc (8 X KT88), with a La Fontaine $23,000 CD player and $11K tower speakers. Amp new is only $3400!

Great sound.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic

What is the recommended Edcor power transformer for the singe-ended KT120 version (not the OddBlock push pull? Thanks much.