stereo SE kt88 build ... abdellah diyaudioprojects design

[88man]

I am just curious if I did the above calculations correctly on PSUD2? It's my first time using the program.

[alexg]

Originally Posted by 88man

Thanks Alexg! I'll use a 560 ohm resistor on the KT88 cathode when using the 400V transformer. This project is a great evolution with many people having contributed to it's design. This is my first build. My experience with tube circuits amounts to only 3 months now, mostly from this forum. Honestly, beyond V=IR and P=[I*2]R, I am really shooting in the dark when I stray from an original circuit. However, I feel that 175ma is not going to give the headroom for stereo operation, and that is why I am aiming for 200ma.

I've tried to figure out PSUD2 for the first time for a 400V transformer @ 200ma. Here are my graphs for the 5U4-G and 5AR4:

Power Supply:
-Transf: Hammond 278X. Prim: 115VAC; Sec: 400-0-400 @200ma
-Caps: ASC Motor Run, 440VAC (600VDC)
-Choke: Hammond 193J 10H, @200ma, 82 ohm

Circuit:

#1: 400V - 5U4G - 40uF - 10H - 50uF - 680R/25W - 50uF in CLCRC: Vmax = 415VDC

#2: 400V - 5AR4 - 40uF - 10H - (2)50uF in CLC: Vmax = 554VDC

#3: 400V - 5U4G - 40uF - 10H - (2)50uF in CLC: Vmax = 471VDC

Questions:
1. I am getting a higher voltage with the 5AR4 (554VDC) than with the 5U4-G (471VDC). Did I do things correctly?...
2. Did I design circuit #3 correctly with a 680R/25W resistor between 50uF(C2) and 50uF(C3) caps?... How will this alteration affect the sound or electrical characteristics of the amp?...


I just checked the Hammond website just after just now, and the 273BX is now listed as 201ma. Everywhere else the Hammond 273BX is rated @ 175ma. Is it a typo or a new transformer?...
Here is the link: Hammond Mfg. - "Classic" Power Transformer - (263-282 Series)

You need to change the load in PSUD2 from the resistor into actual current load that you will be loading the PSU.

For the Abdellah KT88 SE, 160ma for the two KT88 and 8ma for the 6n1p. HTH.

[jmillerdoc]

Here is a Tubecad model of the SRPP stage I am going to try in place of the original gain stage.
Jeff

[porkchop61]

I've found over the years that all of the Hammond transformers are conservatively rated. You can ask a little more of them and get away with it. Again though, a bigger PT will run cooler
I had a case though where I went up a larger size on the PT and had to add power zeners between the center tap and ground to get the voltage down where I wanted it.

JMTC
Glenn

[88man]

Alex, Glenn, and Jeff - You guys have been awesome! Here is my second simulation ever on PSUD2. I used the sum of 168ma as the total load current, where the KT88 pair bias is 180ma + the 6N1P bias is 8ma (Hope that's the way). I assumed the internal resistances on the ASC caps to be 1 ohm each.

1. 400V - 5U4G - 40uF - 10H - 50uF - 80R - 50uF (mine): V(I1)= 405V

2. 400V - 5U4G - 40uF - 10H - 100uF: VI1)= 426V

3. 375V - 5U4G - 10uF - 10H - 100uF (Alexg circuit): V(I1)=386V

4. 350V - 5u4G - 40uF - 10H - 100uF (Porkchop circuit): V(I1)= 363V

I realized that I didn't use 5U4GB for #3, but the difference between 5U4G and 5U4GB was only 5-6V in the simulation.

Questions:

1. #3 and #4 voltages seem lower and not sure why it's below 400V?...

2. Alexg, I've read that you advocate a LM317 regulator for the 6N1P cathode bias. Is my calculation correct: 1.25/0.008A = 156ohm or 150ohm resistor placed between the A & O pins with the I pin to cathode and O pin to Gnd?...

3. Jeff, can you use a 6DJ8 in the existing circuit by just reducing the cathode resistor to 470 ohms.

Glenn, I've remember reading that Hammonds are conservatively rated. If so, then I might go with either the 350V or 375V and stop losing sleep over my first project. But, this little snag made me more familiar with PSUD2.

Thanks guys!

[alexg]

Also, please check the maximum capacitance after the tube rectifier.

I think (please check this), that the 5u4gb can only have a maximum of 10uf.

[porkchop61]

Per the Sylvania manual it's 40uf max.
http://tdsl.duncanamps.com/dcigna/tu...ia/syl-46g.gif

[scitizen17]

Hi,

Not trying to jump in too bad here, however, I just came across this thread. Thanks so much for all the valuable info. I too am collecting parts for this build. Got all the caps. Where are you guys sourcing the 5H 250R choke? I'm assuming 100 mA is sufficient for these if they can indeed be found. Thanks.

[Zekk]

Pardon me for chipping in .. I'm a newbie .. but am puzzled by all this talks about Tubecad, SRPP & PSUD2 which I'm totally ignorant.

Built mine according to porkchop's drawing, and everything is within spec and above all, sounds so sweet , no humming (using 604E of 101db).

This is my first built an it's exhilarating

Thanks guy, for all the great info posted.

Zekk

[scitizen17]

Originally Posted by scitizen17

Hi,

Not trying to jump in too bad here, however, I just came across this thread. Thanks so much for all the valuable info. I too am collecting parts for this build. Got all the caps. Where are you guys sourcing the 5H 250R choke? I'm assuming 100 mA is sufficient for these if they can indeed be found. Thanks.

I think I may have answered my own question. After a little more research it appears that this may be the correct part. The 6N1P maximum anode current will be less than 20 mA, please correct me if I am wrong.

http://www.hammondmfg.com/pdf/5c0032.pdf