200 Watt poweramp with 2 KT120

[es345]

For designer:

here is the result of a bass poweramp only evaluation with 2 KT120. It is running with Anode Voltage of ~850V idle and ~750V under full load. The OT has a separate winding for G2 (40%) running the G2 at ~600V. Primary impedance of the OT is 4K.

This machine is well suited for bass used mainly in clean mode. Very heavy overdrive would exceed the current limitation of the cathode.

[Cygnus X1]

Amazing looking work!

Where did you find those...what are they...terminal boards?
I'm a little skittish about that assembly on top of the filter caps though.

[dynaman]

Yowza! Bad ass!

[David Root]

Hubba! Hubba! Muy Grande Cojones! Looks awesome. Are those C-core transformers?

[surfsup]

Great use of aluminum angle iron for sure. I googled JRE transformers and any other key word I could think up and came up with zilch on those PT/OTs. Who makes 'em?

[es345]

I am from Germany, the most of the parts I ordered locally.

1. Transformers: German company http://www.roehrenendstufen.de/. The core of the transformers are EI130/72 (EI130i). The advantage of this company is that you can order customized OT's and PT's.
2. Terminal boards: Most of them I ordered here http://www.tube-town.net/index.html.

Regarding the assembly of the rectifiers on top of the filter caps: yes that could be done better, but this is an evaluation machine. This solution is good enough for that but not more. The "real build" will be more professional.

[harryk]

Congrats of the new baby. I bet it sounds good. I made last autumn one bass amp with 4xKT-120 power tubes giving some 250-300 W power depending on distortion level. Our band bass player wished to have a real tube monster and he got it. I wonder why people have not used more that particular tube in their projects. I find it very clean and dynamic sounding and it easily replaces the need of 6550/KT88-tubes taking less space in chassis etc.

I am now planning a tube monster for new metal music players using 2xKT-120 giving some 100-150 W output power using only two tubes. I think that it is enough for any guitar player Harry

[xtian]

Back breaker! How much does that amp weigh?

The wire in the trannies looks like coat hanger wire!

[es345]

Here are the dimensions: 50cm*15,5cm*15,5cm, weight 18,3 kg.

Regarding the sound: I have tested it with my Jazzbass over 2 vented 350W cabinets (15 inch Neodym, IMG stage line). It is an amazing clean sound up a to very high sound level. I like it.

Looking to the design itself:
In my next version I wil use a toroidal NT saving 4-5 Kg and I will go to 5K Raa and about 800V Anode at full load.
This should give about the same power with a somewhat reduced current at the cathode

[soma_hero]

Today, finished a bass amp with 2xKT120. Only about 580 on the plates and little less on the screens. Only breaks up at the very end of the volume pot (2 triode stages into LTP with CCS) and sounds really clean and great.

We've been using KT120 in the 300W bass amps my company makes since they exceed to electrical ratings of 6550s and KT88 we've used. Gives a little extra insurance and reliability. The 6550s have had reliability issues as have the KT88s (JJs).

The KT120 is great if you get it well packaged. We ordered bulk from New Sensor, and had to send back most of them due to microphonics. They didn't even put peanuts around them, just packed them up in a big box. That's how to screw up tubes for sure...

But the ones that work sound excellent!

[es345]

Great to hear that this tube is used more and more. Especially for a bass amp this is my favourite one.

Only about 580 on the plates and little less on the screens

What Raa OT value do you use?

[soma_hero]

5000. Hammond 1650R

[es345]

thanks, that means about 100W. I would guess you run the the tubes with 70-80 mA idle each.

Here is a little excel including a diagram which I use for rough estimation of the anode power dissipation and the output power to be expected.
The green cells are the input fields.

[es345]

double post