KT88 PP UL Design Help Needed - Page 3 - 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 10th May 2012, 03:02 PM   #21
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Chuck Hollander is a name that comes to mind on that . It's very complicated . I did tell Sid off about it . It is in place of a big choke . The ripple was I guess about 15 V . The 37 V dynamic range of the LM317 copes with that . Problem is it must not swing further . Transient can kill it . I speculated that if the transformer was split somehow it only need see the ripple and not need the protection . LM317 is fast enough for a class A if wondering . It is a bit like making LP's from CD as sometimes happens this idea . Slightly wrong yet it works .
  Reply With Quote
Old 10th May 2012, 03:05 PM   #22
diyAudio Member
 
Join Date: Apr 2012
For 100W output from a pair of KT88's the data sheet gives a -75V (Vg1). Should I use this voltage or half of this voltage on the plate I vs E plots? The individual lines shown do not include -75V. Do I need a different plot? -37.5V gives a current up above 200mA this seems really high. If I extrapolate a line at -75V I would get a current of 0mA at 560Va which seems too low. From what I see B+=560, Eg1=-58.6 to give Ia=50mA???

JW
  Reply With Quote
Old 10th May 2012, 03:18 PM   #23
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Here are a some typical operating points for KT88

TDSL Tube data [KT88]

Putting your 560V B+ and a 4.5K output transformer into Broskie's PP calculator software yields a bias voltage of -68V for AB1. The software is for PP triode only, but this would lead me to believe that you'll need close to -75V.

Last edited by boywonder; 10th May 2012 at 03:37 PM.
  Reply With Quote
Old 10th May 2012, 03:23 PM   #24
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Listening #111 | Stereophile.com

Didn't find what you wanted will ask friends . It says here hum was very good . No idea why he did it . Sid was a musician . It must have sounded better .He used Quad ESL 63 's if wondering .

I wasn't in the slightest bit interested in valves as we call them at the time ( about 1999 I think ) . I met Sid through a friend and had virtually no idea who he was . He talked me into believing capacitors mattered as he had just discovered it himself . I knew before him about it . I said nothing . He had a child s fascination about things . He wasn't high flung you know . He said he always needed other engineers to help .
  Reply With Quote
Old 10th May 2012, 04:47 PM   #25
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Default Eat as much as you can

Technical books online

This is like those buffet meals that say eat as much as you like . Happy reading
  Reply With Quote
Old 10th May 2012, 05:05 PM   #26
limono is offline limono  United States
diyAudio Member
 
Join Date: Mar 2007
Quote:
Originally Posted by nigel pearson View Post
I can never get my head around them . I was taught by Sid Smith the designer of Marantz amps . He gave up . He agreed my way works . Very nice man was Sid . Sid used LM317 for HT smoothing . It was arranged to work at 400 V and was a famous modification . I always would use cathode bias as it adjusts the KT88 as it ages . Sid always triode connected his amps at home . Sowter in UK make transformers about as good as SIds .
I had Art Audio Concerto triode/UL kt88 with variable feedback and cathode bias. One of their early units made in GB-terrible workmanship ,excellent sound I regret I did not copy schematic and manual .It was the best sounding KT88 PP amp I heard to date.
  Reply With Quote
Old 10th May 2012, 05:10 PM   #27
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Default Art

I think it is a standard circuit with good transformers .
  Reply With Quote
Old 11th May 2012, 06:47 AM   #28
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Quote:
Originally Posted by jwsplatjw View Post
For 100W output from a pair of KT88's the data sheet gives a -75V (Vg1). Should I use this voltage or half of this voltage on the plate I vs E plots? The individual lines shown do not include -75V. Do I need a different plot? -37.5V gives a current up above 200mA this seems really high. If I extrapolate a line at -75V I would get a current of 0mA at 560Va which seems too low. From what I see B+=560, Eg1=-58.6 to give Ia=50mA???

JW
With todays KT88's, keep Iquies low; or they won't last long at 560V and the business gets costly.

Decades ago, KT88 UL circuits were about that showed Iquies 60mA at 600V+, a non-survivable grilling for todays tubes. That's the reason I went to parallel push pull.

richy
  Reply With Quote
Old 11th May 2012, 11:48 AM   #29
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Default Gu 50 ?

What about the Russian version GU 50 ? It is worth a look . It was what the Germans came up with about 1942 and think was called a Ray Pentode . Time is running out to buy these . Telefunken LS 50 and Chinese FU 50 also .

GU-50 - Wikipedia, the free encyclopedia

http://www.qrz.ru/reference/tubes2/type3/gu50.shtml

Last edited by nigel pearson; 11th May 2012 at 12:03 PM.
  Reply With Quote
Old 11th May 2012, 01:39 PM   #30
diyAudio Member
 
Join Date: Apr 2012
This forum is great, my learning has taken leaps since I posted my questions.

I have decided that yes, 560 V is too high and am looking now at 460-480V depending on what I use for a driver tube, if I can use the same B+ for both it reduces the complexity and the part count. It also means I can use the 21st century Maida regulator. Tom has already done the heavy lifting and is selling kits.

So now I need to get my driver up to snuff. At present I have a single 6SN7 drawn as a LTP which will take a 3.5V up to 124V or about 35 times. It has been suggested to me that I will need more gain when I add the NFB of between 14-20 dB. So now I am considering a pair of 6SN7's wired as a cascode LTP. Can I calculate the gain by finding the gain for a cascode then divide by two for putting it in a LTP?
  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
With a little help... KT88 PP UL Amp Herr Grau Tubes / Valves 105 15th January 2013 04:02 PM
PP-UL amp with KT88 misterno Tubes / Valves 1 27th July 2011 05:47 PM
modifying kt88 pp ul amp iorga Tubes / Valves 25 6th March 2010 08:29 AM
My new pp KT88 design baggystevo82 Tubes / Valves 41 16th May 2005 02:02 PM
Possible to make a KT88 PP UL schemat OTL ? Layberinthius Tubes / Valves 3 5th February 2004 03:59 PM


New To Site? Need Help?

All times are GMT. The time now is 10:25 AM.


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