stereo SE kt88 build ... abdellah diyaudioprojects design

[scitizen17]

Originally Posted by scitizen17

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

Whoops, forgot to include the part#: 155H

[88man]

Thanks Alex and Glenn. I'll try to stay within the limit of the 5U4-G. The power trans is my last purchase, if all is well, this is the CLC PSU that I'll use:

Hammond 274BX 375V @ 175ma
Sovtek 5U4-G
10uF to 40uF for C1 (ASC motor run)
10H 200ma choke (Hammond 193J)
(2) 50uF parellel = 100uF total for C2 (ASC motor run)

PSUD2 simulations:
- Assuming "off-load current" is 375V (rated voltage), then a 40uF C1 yields 392V B+.
- Assuming "off-load current" is 392V (1.05X rated voltage), then a 10uF C1 yields 410V B+.
Close enough...

Questions:
1. How do you calculate ripple on PSUD2 for the above circuit?...
2. Alex and Glenn, what are your PSUD2/measured B+ voltages on your PSU?...
3. To calculate the resistor value for a LM317 regulator for an 8ma 6N1P cathode bias, is this right: 1.25/0.008A = 156ohm resistor?...
(resistor placed between the Adj & Out pins with the Inp pin to cathode and Out pin to Gnd)?...

Thanks again, guys!

[porkchop61]

My measured B+ voltages are listed on my web page for various tubes:
http://webpages.charter.net/porkchop...issipation.jpg
I used 175mA for my load:
http://webpages.charter.net/porkchop...wer_supply.jpg

[scitizen17]

Originally Posted by scitizen17

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

Has anyone built this design using the 5H choke/10uF capacitor for the plate source of the 6N1P?

Is this additional filtering pointless?

[porkchop61]

I'm also curious about this, I personally haven't tried it on my build.
What is the point in adding these components? Is it for decoupling, filtering?

Glenn

[scitizen17]

Originally Posted by porkchop61

I'm also curious about this, I personally haven't tried it on my build.
What is the point in adding these components? Is it for decoupling, filtering?

Glenn

Could this be possible?: If you calculate the LC filter formed by the 5H choke & 10uF cap, and based on 10mA current for the 6N1P plate current, this should provide 29dB of filtering for the 120Hz AC component of the B+. It should also drop the B+ by 2.7V

I have also read that the use of a plate choke will increase the dynamic range of the preamp tube.

I'm not an expert by any means, so someone please chime in.

[scitizen17]

Originally Posted by scitizen17

Could this be possible?: If you calculate the LC filter formed by the 5H choke & 10uF cap, and based on 10mA current for the 6N1P plate current, this should provide 29dB of filtering for the 120Hz AC component of the B+. It should also drop the B+ by 2.7V

I have also read that the use of a plate choke will increase the dynamic range of the preamp tube.

I'm not an expert by any means, so someone please chime in.

Hello,
I noticed that you added a 1K resistor feeding the control grid of the KT88. Can you tell me about this?

[jmillerdoc]

Originally Posted by 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.


Zekk

Zekk,
I wanted to have a more symetrical layout on my chassis with some flexibility on the preamp/gain stage so I actually have built this with x2 6N1P tubes and plan to try it 2 different ways. One will be the original circuit using 1/2 of 2 seperate 6N1P or 6JD8 tubes. Then I will try the SRPP circuit above in place of the orginal gainstage. The SRPP requires a whole 6N1P (twin triode) for each channel.

The PSUD2 is a power supply modeling software available free at Duncanamps.

Jeff

[jmillerdoc]

Originally Posted by 88man

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

Thanks guys!

Actually my plan was to parallel a 1K with the original 1k to get 500R (470R). So in essence, yes.
Jeff

[porkchop61]

Originally Posted by scitizen17

Hello,
I noticed that you added a 1K resistor feeding the control grid of the KT88. Can you tell me about this?

That's a grid stopper resistor. I'm just used of putting them in my guitar amps for oscillation prevention. I'm not sure it's needed in this amp, as I haven't scoped it to see if this is happening.
Here's my post on the need for this part:
Grid stopper resistor required (KT66)?