Stereo build- Mikael Abdellah's KT88 SE amp

[cryo]

Here is the undercarriage.

[porkchop61]

I like the nice compact layout! I wish mine was a little smaller, and lighter
Who's power transformer is that? I personally prefer the lay-down type transformers.
Good work.

Glenn

[EDIT]
You've got to try the LED biasing for the 6N1P, VERY nice sounding!

[mhouston]

I think this thread is still about SE KT88s and the like. I just built a SE amp which started with KT88 but found the Back Sable EL34s gave more power and and better frequency response. I wanted to bring back the Bread Board amp (BBAmp said Be Bamp) but wanted it to look more than a science experiment. To this end I used a highly sanded and multi-beeswaxed Australian pine board and hid the wiring. Also the ugly Edor open OPTs were canned which also provided a fixture for the RCAs and speaker binders.

In this build there is no driver stage. I hope there was enough drive from my two stage tube preamp but this failed. So after cathode current and HT+ was increased matched Black Sables EL34s replaced the JJ BLue Glass KT88s to acheive more gain. Also a high performance OPAMP preamp (Prada627) was placed between my upgraded Oppo 980H and tube pre to give sufficient gain and drive. The amp is exceptionly quiet. PS has 100uf cap-10H 200mA choke-100uf cap. The quietest amp I have ever built. No NFB of course.

Through my 91db efficient Osborn Eclipse three ways towers there is plenty of volume. The amp tested 17hz to 47Khz with a 5.6ohm resistive load (speakers are 6ohm). The sound is neutral, very transparent with exceptional blacks.

[mhouston]

Originally Posted by cryo

Someone asked if there were any other builders besides Sherman. This is my iteration. Sherman actually helped me a lot on this.

It is very nice sounding, won't drive anything big, but that's not my need.

Good luck with yours!

-cryo

Beautiful craftsmanship. very well done. Million dollar base.

Here's a few of my latest SE UL/Triode KT88 offerings. I'm building under the retro-thermionic banner.

[mhouston]

I had recently posted under this thread that I used Black Sables in my Be Bamp. I had to go back to KT88s. Reason being I was pulling about 32 watts RMS from the Sables which would have stuffed them very quickly. I have gone back to the JJ Blue Glass KT88s which can take the 365 volts plate to cathode and the 92mA cathode current.

I have picked up a bit more bottom end and when driving my entire system I can get 25hz into the speakers as a lower 3db point. Even 20hz is quite audible. This has been tested with a function generator at the preamp right through the entire system. Max power is 6W RMS at 1Khz into the speakers which are 6 ohm and bi-wired.

Seeing this is the Mikael Abdellah KT88 thread I must add that this is the third of his style amps that I have built. And for this bread board build I am going to build remote swapable driver stages which will share the PS from the original bread board amp. I will be able to swap in and out different front-end driver stage. DIY decadance.

[mhouston]

I think I have scared every one else away. Anyway I built a remote driver stage for my bread board SE UL KT88. It is the original stage Mikael used. Except in this case I upped the cathode by-pass caps to low ESR 220uf caps which are snubbed with 220nf polies. I used the Russian military caps (0.22uf) for the interstage caps added a 220 ohm grid block resistor and a 470K resistor from grid to ground.I don't use a volume control here.

I built the driver stage in a Tea Box which is lined with bitumanised Al foil. I used a 7 pin plug to carry the 400V and filament voltage. I can now build other driver stages and try them against the power stage.

[mhouston]

I would hate to see this thread go cold.This is my retro-thermionic Pinot "KiSharn" for which I am very proud. The best amp I have ever built. I don't think I have posted it on this site but if I have - forgive me. This is a two stage SE amp a true SET.

The amp is small and based on the 6AS7 tube for which now I have a lot of respect. The tube is also badged the 6080. The driver is a 40 year old Australian made AWA 12AX7 and the rec. tube a rare JAN CBXL-5R4GY brown base.

Once more the amp base is Mirbeu. I sprayed the top plate blue to match the Edcor OPTS. No input caps but the inter-stage caps are the same as used on my Twinnings Tea box preamp - Jensen pure copper, paper and oil.
There is two ferrite chokes on the power cord plus a complete power filter under the bonnett. The PS is tube rectified and choked. The power tube is a Svetlana "Winged C". Low ESR caps and a mix of carbon and metal oxide resistors are used.
Though only a 3W output this baby goes 12hz to 50khz on -3db points. Bass is weighty and deep and mids are detailed and heavily textured.

[arold19]

There's the original schematic of Mikael Abdellah Single-Ended (SE) KT88 / 6550 Tube Amplifier Schematic and there an other one KT88 Single Ended (SE) Tube Amplifier using a 5H inductor between the 400V + and the GN1P tube. Is that an upgrate? How much rate "rate" need this choke... 0.02A???

Thank you.

[scott17]

Originally Posted by arold19

There's the original schematic of Mikael Abdellah Single-Ended (SE) KT88 / 6550 Tube Amplifier Schematic and there an other one KT88 Single Ended (SE) Tube Amplifier using a 5H inductor between the 400V + and the GN1P tube. Is that an upgrate? How much rate "rate" need this choke... 0.02A???

Thank you.

Each channel of the 6N1P draws about 4mA, so the 0.02A choke would be fine. I used a Hammond 155H, one for each channel. Many folks did not use the choke in their build, but I believe it can provide better filtering in conjunction with the 10uF capacitor.

[mhouston]

Originally Posted by scitizen17

Each channel of the 6N1P draws about 4mA, so the 0.02A choke would be fine. I used a Hammond 155H, one for each channel. Many folks did not use the choke in their build, but I believe it can provide better filtering in conjunction with the 10uF capacitor.

Choked PS(s) in both SS and tube amps will always sound better. This is not just my belief but also that of some very well known amp builders. Try Hugh Dean to start with.

Most try to drop the choke because of cost, weight, chassis realestate and even looks. But some very pricy preamps etc. come choked. Then there is tube rectification. But that's another thread.