Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Which KT66 is the best?
Which KT66 is the best?
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 3rd January 2018, 09:12 PM   #1
mbrennwa is offline mbrennwa  Switzerland
diyAudio Member
 
mbrennwa's Avatar
 
Join Date: Mar 2005
Location: Zurich, Switzerland
Default Which KT66 is the best?

I recently tried to clean up my cellar. I found a bunch of parts that nicely fit together, so I designed and built a new tube amp (Mac Gyver style!). The power stage uses a pair of triode connected KT66 tubes in push pull mode. The general approach to the amp is classic, but there is some help of a sand CCS, a choke plate load (yes, that was also among the parts I found), and an active control for the power tube bias currents.

While designing and building the amp, I got distracted with reading about KT66 tube quality. Some comments touted the NOS GEC KT66 with coated glass (grey glass) as "the best". Sooo, while I was at it, I tested all my 23 KT66 tubes for harmonic distortion in my Mac Gyver amp. The result was, well, a bit boring. As long as the tubes were matched ok, distortion was almost the same for all tubes I tested. I don't know if they sound different, but in terms of harmonic distortion the make/brand, glass coating, base color, or gravitational field anomalies at the production plant did not matter. The numbers are in the attachment, just in case someone is interested.
Attached Files
File Type: pdf KT66_test_20180102_mbrennwa.pdf (57.4 KB, 104 views)
__________________
[ audioroot.net | hifibau.ch ]
  Reply With Quote
Old 3rd January 2018, 09:42 PM   #2
JonSnell Electronic is online now JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Good point.
Using different valves can make a difference if not biased correctly.
Being from and being brought up on different makers, I found that they are all of a muchness ... no, all within the designated specification. It is only when one steps outside that one finds a Svetlana EL34 or KT88, (KT120 is a new idea) will give more power, because it is not the same specification.
My 1965 XLCH 1000cc Harley has never had the heads off for any major maintenance. How many Yamaha bikes can boast that!
Go by the specification, any good quality manufacturer will meet or exceed it.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 4th January 2018, 01:36 AM   #3
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
KT66 were just made by the english MOV subsidiary of GEC, so the only differences you will find between KT66 is due to manufacturing changes. There is a date and factory code to clarify manufacture, and the external differences of base colour, and internal graphite coating will indicate date ranges, and there was a late change in getter cup/halo.
  Reply With Quote
Old 4th January 2018, 05:07 AM   #4
FullRangeMan is offline FullRangeMan  Brazil
diyAudio Member
 
FullRangeMan's Avatar
 
Join Date: Aug 2009
Location: Brazil
I was told the KT66 is more linear for audio than other KT, this is correct?
What is the KT66 sound quality aside EL34 and KT88?
Thanks
__________________
>Never go to a psychiatrist, adopt a cat or dog from the streets. On the streets pets live only two years average.
  Reply With Quote
Old 4th January 2018, 05:36 AM   #5
trobbins is offline trobbins  Australia
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
It's just a valve.
  Reply With Quote
Old 4th January 2018, 06:44 AM   #6
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
Your amplifier uses linear circuits, plenty of gain, push pull KT66s in triode mode, and negative feedback. The amp distortions are likely less than most loudspeakers that are driven with 5 Watts.

Try using the same basic amp, but modify it for a little less gain, and remove the negative feedback (all this may be easier said than done properly).
Now do your distortion measurements at 5 Watts, with different pairs of the KT66s.
Then listen to the different KT66 pairs, perhaps at a level of 5 Watts.
Now what do you measure?
Now what do you hear?

Last edited by 6A3sUMMER; 4th January 2018 at 06:49 AM.
  Reply With Quote
Old 4th January 2018, 06:50 AM   #7
globalplayer is offline globalplayer  Germany
diyAudio Member
 
globalplayer's Avatar
 
Join Date: Oct 2014
Location: =)
White noise?
__________________
◢◣◢◣◢◣◢◣◢◣
  Reply With Quote
Old 4th January 2018, 07:03 AM   #8
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
On second thought, for the modified amp, do all the tube pairs testing at 1 Watt.
That will make a good comparison to the distortion of original amp configuration.
Then listen at 1 Watt to the best, and worst tube pairs.
  Reply With Quote
Old 4th January 2018, 07:08 AM   #9
globalplayer is offline globalplayer  Germany
diyAudio Member
 
globalplayer's Avatar
 
Join Date: Oct 2014
Location: =)
Good idea.
__________________
◢◣◢◣◢◣◢◣◢◣
  Reply With Quote
Old 4th January 2018, 08:25 AM   #10
mbrennwa is offline mbrennwa  Switzerland
diyAudio Member
 
mbrennwa's Avatar
 
Join Date: Mar 2005
Location: Zurich, Switzerland
Quote:
Originally Posted by FullRangeMan View Post
I was told the KT66 is more linear for audio than other KT, this is correct?
What is the KT66 sound quality aside EL34 and KT88?
Thanks
Last time I looked at the curves of these tubes, the KT66 in triode mode looked the most linear to me. Just look at the curves and decide yourself.
__________________
[ audioroot.net | hifibau.ch ]
  Reply With Quote

Reply


Which KT66 is the best?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Williamson Amp: KT66 Alan Frobisher Tubes / Valves 10 21st November 2017 05:45 AM
Osram KT66 lpd Swap Meet 0 2nd November 2012 07:01 PM
KT66 Woes lpd Tubes / Valves 2 31st October 2012 02:51 AM
6BG6 for KT66 exurbia Tubes / Valves 4 23rd November 2008 02:09 PM
NEW KT66's Trout Tubes / Valves 18 7th February 2007 07:08 AM


New To Site? Need Help?

All times are GMT. The time now is 04:09 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki