Stereo build- Mikael Abdellah's KT88 SE amp

[porkchop61]

I think I'd like to start a new thread on this topic as it might help others when doing this build.

For a little background,
I'm in the process of building a stereo version of this project.
I've built 4 guitar amps, but this is my first hi-fi project. This is also my first non push-pull build, so I have a few new questions.

Sherman has been helping me with a lot of my questions, so I'm very grateful to him for all the advice.

Stay tuned, and I'll post pix as my build goes along.

Has anyone else built this design (other than Sherman), and if so, what to you think of the sound?

Thanks.
Glenn

[porkchop61]

Here's the last few questions I had on this topic to move this thread:

Originally posted by porkchop61
What voltage did you use for your .22uF Auricap coupling capacitors, 450V?
I just finished my "turret board", and all I need to order now are the 2 coupling capacitors. The Kimber Kaps look good from Parts Express.
Thanks
Glenn

Originally posted by Sherman
I did use the 450V Auricaps. I think they sound very, very good and the price is not too bad.

I considered all the usual suspects but the Auris were easily available and have a good reputation. At the time I didn't remember PE having the Kimbers available but if I were building today I might well use them.

Originally posted by porkchop61


Thanks Sherman. I only have to buy 2, so price isn't that much of an issue .

On another topic, I'm looking at the wiring diagram for the Hammond 1628SE OT's. On the primary side they list the the blue lead as common, then there is a red lead and a blue/yellow lead for the 40% screen tap. My question is, does the B+ go to the black lead, and the plate of the KT88 go to the red lead, or the other way around? I assume the screen (pin #4) of the KT88 goes to the 40% screen tap.

This is my first SE amp, I'm used of PP designs so this is a little different.

Thanks for all your help!
Glenn

BTW: I'll be posting pix of my progress as I go along. I just got my 1/8" thick aluminum chassis plate from UPS today. I'm going to work on the red oak base this week.

[porkchop61]

I haven't heard back from anyone on this question, so I thought I'd ask again.
Does the red lead on the OT go to B+, and the black lead go to the plate of the KT88, or is it the other way around.
I assume this makes a difference, as the screen tap is not at 50%, otherwise I don't think it would matter.
Thanks
Glenn

[porkchop61]

Has anyone ever used a cap-resistor-cap for power supply decoupling in the power supply of this amp?
I typically do this for all my guitar amplifiers. I usually use (2) 50uF 450V electrolytics, and a 10k 1 watt in between the caps.
If anyone has done this, what did you use for the resistor and capacitor values?
Thanks in advance.
Glenn

[Simpleton]

Glen, here's the answer to your tranny question:

http://www.hammondmfg.com/1627.htm

As for the second one...i'll let it to those more enlightned.

BTW, i showned my amp to some friends and they were amazed by the sound quality of it (i was expecting that ). They had never heard tube sound, and even though the amp was strugling at 88dB speakers at max volume, they couldn't hear distortion (that's the "difference" between sand and hollow state gear).

So, go on with the project Glen!

[Sherman]

Originally posted by porkchop61
Has anyone ever used a cap-resistor-cap for power supply decoupling in the power supply of this amp?
...

When playing my amps at high volume on a passage with a lot of bass I got some LF oscillation. I put in a decoupling filter but used only 1 resistor followed by a 47uF cap then the plate resistor. I adjusted the values of the resistors (can't remember what I ended up with off the top of my head) to get about the same plate voltage on the 6N1P. It cured my oscillation.

[Sherman]

Originally posted by Simpleton
Glen, here's the answer to your tranny question:

http://www.hammondmfg.com/1627.htm

...

So, go on with the project Glen!

Simpleton,

Today I finally plugged in the 6922 in place of the 6N1P. I haven't done any measurement and it is hard to do A/B tests as I don't have a balance control on my preamp, but it sounds at least as good as with the 6N1P.

[Simpleton]

It's good to hear that Sherman, i'm glad
Oh, if you happen to get hum problmes after this mod, try to change brands for the 6922/E88CC

[porkchop61]

Originally posted by Simpleton
Glen, here's the answer to your tranny question:

http://www.hammondmfg.com/1627.htm

As for the second one...i'll let it to those more enlightned.

BTW, i showned my amp to some friends and they were amazed by the sound quality of it (i was expecting that ). They had never heard tube sound, and even though the amp was strugling at 88dB speakers at max volume, they couldn't hear distortion (that's the "difference" between sand and hollow state gear).

So, go on with the project Glen!

Thanks Simpleton, but that's where I started.
The Hammond schematic still does not tell me which lead goes to the B+.
I think what's confusing me is the label of "common" on the black lead.
Does this go to the plate on the KT88, or to the B+?

Again, this is my first SE amp,
I'm more familiar with PP designs as on all my guitar amps.
Glenn

[porkchop61]

Originally posted by Sherman



When playing my amps at high volume on a passage with a lot of bass I got some LF oscillation. I put in a decoupling filter but used only 1 resistor followed by a 47uF cap then the plate resistor. I adjusted the values of the resistors (can't remember what I ended up with off the top of my head) to get about the same plate voltage on the 6N1P. It cured my oscillation.

Thanks Sherman.
I thought I'd have to play around with the values anyway.
I always have to do this on my guitar amps.
I'm still learning all these "Hi-Fi" tricks
Guitar amps are pretty narrow frequency-wise as compared with this stuff.

Thanks for all the help.
Glenn