I've put loadlines aside for a while... - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd May 2003, 09:12 AM   #1
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
Question I've put loadlines aside for a while...

but, I could use som thought on another problem.

Here is the amp I'm building. http://213.67.45.70/se_kt88_3.gif

When I firts tested the circuit I noticed that the input stage clipped quite early wich was expected. However, on my inital measurements on just the input stage I got almost 120V PP signal, but when I hooked it up to my KT88 I didn't even get half of that. Then I got an idea. I knew that the 6n1p didn't have any problem driving a 470k load, so I inserted a 470k resistor right after the 0.22uF cap. That way the lowest possible load for the input stage would be 470k. (This is just a crazy test) Now I got my 120vpp again. But instead the KT88 clips almost as early as the 6n1p did before. Clipping only occurs at one side of the signal. I've posted a question similar to this one just a couple of weeks ago, but that time, I wanted to know if it was possible to offset the input stage. This time I wonder if it's posible to offset the KT88 so that it doesn't clip so early. One half of the 6n1p shouldn't be able to drive it into clip, should it???
  Reply With Quote
Old 2nd May 2003, 02:21 PM   #2
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default KT88.

Hi,

Have you checked the bias on the KT88 ?

Cheers,
__________________
Frank
  Reply With Quote
Old 2nd May 2003, 02:27 PM   #3
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
I have roughly 36V at the cathode. When I had a 470ohm resistor I got 68mA at the plate and 8mA at the screen. This might be a little low, but the next resistor value seem to be 330ohm which I think might be a bit too low. I tried it breifly and I think I got something like 90mA at the plate and 10mA at the screen.
  Reply With Quote
Old 2nd May 2003, 02:39 PM   #4
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default RE:KT88

Hi,

Taken from the E12 series of resistors the next value dowm from 470R would be 390R.

Cheers,
__________________
Frank
  Reply With Quote
Old 2nd May 2003, 02:40 PM   #5
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
Sounds great. Any idea where I can get a 390 resistor? Preferably a low/non-inductive type.
  Reply With Quote
Old 2nd May 2003, 02:46 PM   #6
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default RE:RE:KT88

Hi,

Haven't checked but Farnell could have those.

Cheers,
__________________
Frank
  Reply With Quote
Old 2nd May 2003, 02:47 PM   #7
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
Great! Thanxx!!
  Reply With Quote
Old 2nd May 2003, 04:14 PM   #8
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
330ohm try it..as long as the plate dissapation is not exceed what is the problem?

90mA and around 360vdc on the plate???

Would give you 32,4 watts of dissapation...the KT88 can handle 35Watts..
  Reply With Quote
Old 2nd May 2003, 04:27 PM   #9
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
But I have 400V at the plate. What do I have to gain from running the tube a bit hotter?

[edit]

When I have 36V at the cathode... Do I in reality have 400V-36V at the plate?
  Reply With Quote
Old 2nd May 2003, 04:35 PM   #10
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Do you have 400v on the plate? or 400v b+ connected to the transformer.....?

Remember the transformer drops around 20-40v..
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Mikael Abdellah's kt88, (LOADLINES) soundbadger Tubes / Valves 6 3rd January 2012 03:30 AM
Steve Bench PP loadlines Klimon Tubes / Valves 0 8th November 2006 03:25 PM
loadlines for newbie. bloozestringer Tubes / Valves 6 4th September 2006 08:41 PM
Any software out there for taking the headache out of composite loadlines? aletheian Tubes / Valves 0 17th November 2005 02:30 AM


New To Site? Need Help?

All times are GMT. The time now is 04:40 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2