Biasing at 3.2V is about twice the current of the original circuit. To run this tube correctly, biased at 3.2V, you would be running at 8mA instead of 4mA. The plate resistor would be 22.2K. Conventional RC cathode resistor would be about 400R.
Have not used a CCS in this circuit. May be worth a try.
I would say try the circuit as designed first, 47K plate resistor, 1K cathode resistor, then proceed from there.
Scott
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You could also run at 3.2V bias with a 33K plate resistor at 6mA. It can be calculated several different ways. Just follow the load lines.
I have been looking at the curves and will try a few operating points. I will of course build it stock and then experiment with it. Should be a lot of fun.
I want to try the led bias and maybe a ccs plate load.
looking forward to building the amp
Debra
I want to try the led bias and maybe a ccs plate load.
looking forward to building the amp
Debra
Finished building the amp. What a great sounding amp. Very warm and detailed.
It was a lot of fun to build.
Debra
It was a lot of fun to build.
Debra
Wow Debra! No time like the present so they say. That was very quick. What are you going to do tomorrow? 😀
I'm very glad you like the amp. Looks great! What are those KT88s? EAT?
I suppose experimentation with the driver cathode bias is next?
Best regards,
Scott
I'm very glad you like the amp. Looks great! What are those KT88s? EAT?
I suppose experimentation with the driver cathode bias is next?
Best regards,
Scott
The KT88s are Shuguang Treasures. I have been very impressed with the Treasures and Psvane line of tubes.
Next I want to play around with led cathode bias. I also want to experiment with a CCS, I have some DN2540 mosfets in my parts bin I can use.
The amp is great as it is, it is dead quiet, and there is something to be said about it having no sand. But I like to play around and tweak things.
Debra
Next I want to play around with led cathode bias. I also want to experiment with a CCS, I have some DN2540 mosfets in my parts bin I can use.
The amp is great as it is, it is dead quiet, and there is something to be said about it having no sand. But I like to play around and tweak things.
Debra
Been putting the amp through it's paces. Just played the album I always play first with a new amp. UHQR vinyl release of Supertramp Crime of the Century.
Other components used are a Bottlehead extended foreplay preamp, Bottlehead Eros phono stage. Speakers are Madisound BK-20 backloaded horns,with Fostex FE206 drivers.
The amp is dead quiet, quieter than my DIY 300b amp
On rock music the amp sounds better than my 300b amp. The Bass is deeper, and the music has great presence. Very good sound stage. I can sit on my couch with my eyes closed and easily become immersed in the music.
On solo piano music that I like to listen to alot. It is close to my 300b amp. The 300b is slightly more liquid and more detailed.
In all fairness, I expect this amp to improve as it breaks in. I didn't take the time to preburn in the coupling capacitors. The Mundorfs silver/gold oil I used in the build take a little time to smooth out, and the tubes are new also.
After some burn in time I will play with LED bias on the 6N1P, and maybe a CCS plate load.
All in all this is a fantastic sounding amp! The circuit layout is very well thought out. The instructions are very well done and the amp is a lot of fun to build.
Debra
Other components used are a Bottlehead extended foreplay preamp, Bottlehead Eros phono stage. Speakers are Madisound BK-20 backloaded horns,with Fostex FE206 drivers.
The amp is dead quiet, quieter than my DIY 300b amp
On rock music the amp sounds better than my 300b amp. The Bass is deeper, and the music has great presence. Very good sound stage. I can sit on my couch with my eyes closed and easily become immersed in the music.
On solo piano music that I like to listen to alot. It is close to my 300b amp. The 300b is slightly more liquid and more detailed.
In all fairness, I expect this amp to improve as it breaks in. I didn't take the time to preburn in the coupling capacitors. The Mundorfs silver/gold oil I used in the build take a little time to smooth out, and the tubes are new also.
After some burn in time I will play with LED bias on the 6N1P, and maybe a CCS plate load.
All in all this is a fantastic sounding amp! The circuit layout is very well thought out. The instructions are very well done and the amp is a lot of fun to build.
Debra
Been playing the amp a lot over the last two days. Have about 20hrs or so on it. It is noticeably smoother now.
I will let it break in for about 100 hours or so and then try the led bias.
Debra
I will let it break in for about 100 hours or so and then try the led bias.
Debra
LED Bias for beginners
Hi KT88 SE community,
I'm running this amp now for about a year.....
....and I just opened it to try some other components.
Can somebody explain to me exactly what to solder where for LED bias....I build this amp with Scotts excellent manual ...but I feel still like bloody beginner when I hear you talking about circuits aso
Thanks
Gregor
Hi KT88 SE community,
I'm running this amp now for about a year.....
....and I just opened it to try some other components.
Can somebody explain to me exactly what to solder where for LED bias....I build this amp with Scotts excellent manual ...but I feel still like bloody beginner when I hear you talking about circuits aso
Thanks
Gregor
I have read on the forum that it is possible to switch between triode, ultralinear and pentode mode. Is it possible to implement pentode mode on this design?
Its been a year since I first built the kit so I decided to do a rebuild with some tweaks. Heres some pics of the new version. Tweaks: led bias on driver, cap changes to PIO, and a few resistor changes. Still loving every note that sings from this amp.
Attachments
I added LED bias for the 6N1P. I used a pair of HLMP 1302 red leds (Digikey part number 1080-1042-ND) for each cathode. This led has a 2v drop so a pair of them will give about the same bias point the original resistor did.
I bought 10 of the leds and measured the voltage drop across each one and picked the four that were the closest matched. This was probably not necessary, they were all within 0.03v
The led bias made a very noticeable improvement in detail. The music sounded clearer and more accurate. It still very much had the tube warmth, but now with more clarity.
I think it is well worth the upgrade. It is easy to do, and does not cost much (leds $0.46 a piece or $0.33 each if you buy 10).
I think this made enough of a difference that if I were to build this amp again, I would use led bias to start with.
Deb
I bought 10 of the leds and measured the voltage drop across each one and picked the four that were the closest matched. This was probably not necessary, they were all within 0.03v
The led bias made a very noticeable improvement in detail. The music sounded clearer and more accurate. It still very much had the tube warmth, but now with more clarity.
I think it is well worth the upgrade. It is easy to do, and does not cost much (leds $0.46 a piece or $0.33 each if you buy 10).
I think this made enough of a difference that if I were to build this amp again, I would use led bias to start with.
Deb
Hello Deb,
Can you post a simple schematic of how to connect the LED? Cathode side to ground? Should the bypass capacitor stay in place?
Thanks!
Can you post a simple schematic of how to connect the LED? Cathode side to ground? Should the bypass capacitor stay in place?
Thanks!
It is very simple. Connect two leds in series. then connect the string to the tube with the cathode to ground. Remove both the resistor and bypass capacitor
Debra
Debra
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