So i know i have posted a few threads on here and jump around a bit on what my next project will be. But here is the final one. It will be a KT120 SE UL with switchable triode / UL and switchable feedback 0,3,6db . The KT120 will be run at 400v, 105mA, and 3.75K load. Cathode bias. The EL84 driver tube will be run at 400v, 8K load, 200vp, 150v screen, 25mA. The driver will have diode / LED bias and also a unbypassed resistor for global neg feedback. The feedback is taken from the secondary of the OPT.
All iron is Edcor. Dual mono blocks. 400-0-400 / 200mA power transformer. 2x 2H/29ohm chokes per channel. See attached images. One is just the power supply (mono bloc), the other is ripple for the output stage. The PS caps will be ASC oil caps. 5U4 rectifier tubes. Any good places to get the ASC caps? Allied?
Power output will be approx 10W triode, 20W UL (only according to online sims).
Could you look at the Power Supply sim and let me know if there is any glaring issues? Thank you!
More details to come... once i start building it! Probably bread board it first.
All iron is Edcor. Dual mono blocks. 400-0-400 / 200mA power transformer. 2x 2H/29ohm chokes per channel. See attached images. One is just the power supply (mono bloc), the other is ripple for the output stage. The PS caps will be ASC oil caps. 5U4 rectifier tubes. Any good places to get the ASC caps? Allied?
Power output will be approx 10W triode, 20W UL (only according to online sims).
Could you look at the Power Supply sim and let me know if there is any glaring issues? Thank you!
More details to come... once i start building it! Probably bread board it first.
Attachments
KT120 load? i simulated 3.75K vs 5K and wondering whether i should go with the 5K load. A little less power output but distortion drops. Thoughts?
No glaring issues, nice project, a little off mainstream with EL84 as a driver, go for it! Do run the KT120 in a similar fashion since quite a while, 460V@110mA on 3k5, driven by a C3M pentode. Still one of my favorite amps indeed!
any recommendations of a 3.5k vs a 5k output transformer? either one i can run it a bit hotter at 420v and 120mA. 10v drop on the OPT and 40v bias is still around the 470v . Using a 5AR4 will get me the 470v.
Last edited:
Did not verify 5k in comparision to 3k5. I use some nfb to decrease output impedance, do not recall how many db out of the top of my head though. It behaves well on different type of speakers.
Just wondering what would be "better" the 5K or 3.5K transformer? i guess its really personal preference... but seeing if anyone has any opinions about it?
Difficult. I'm sure research was done on operating points of a KT88 on different loads. But the KT120 is different. Perhaps you can find something on KT88 and assume the KT120 behaves ballpark like the KT88. I just have no experience. Except to say that I built an amp for a buddy of mine that uses a 5K output transformer and KT120 as output tube and that amp sounds fine.
yeah i am leaning towards the 5K as the output transformer. What did you use for driver tube if you don't mind me asking?
Last edited: