Matching tubes for PP - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs 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

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
Thread Tools Search this Thread
Old 14th November 2010, 01:23 PM   #1
diyAudio Member
h00hbt's Avatar
Join Date: Jun 2007
Default Matching tubes for PP

Hi all

How important is it to use matched output tubes in a stereo integrated amp?

  Reply With Quote
Old 14th November 2010, 01:58 PM   #2
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
Depends on bias arrangements. Most critical is fixed bias, but shared between both valves. Least critical is cathode bias, separately for each valve.

Also depends on how dependent the amp is on output stage balance to eliminate hum from HT ripple.

This is balance within a PP pair. Balance between channels is less important, unless there is no global feedback.
  Reply With Quote
Old 14th November 2010, 04:43 PM   #3
diyAudio Member
artosalo's Avatar
Join Date: Feb 2010
How important is it to use matched output tubes in a stereo integrated amp?
I have once studied this subject.
I summary, quite different kind of tubes can be used in PP-amplifier with very low distorton values. This requires - in case of fixed bias - that the bias of both output tubes can be adjusted separately to same cathode current and the output of phase splitter AC-voltages can also be adjusted to minimum output distortion.
  Reply With Quote
Old 19th May 2011, 03:13 PM   #4
diyAudio Member
trobbins's Avatar
Join Date: Feb 2009
Location: Melbourne, Oz
I suspect that if any global feedback was disconnected, then measurement of output distortion as signal rises would be a good determinant of output stage valve matching, as it measures a consequence of imbalance across the whole dynamic range - both from the valves and their imbalance effect on the OT.

It would be interesting to know if anyone has checked this for a reasonable number of matched/unmatched pairs to appreciate the spread in distortion levels experienced.

Another measurement for fixed bias PP could be to meassure the voltage signal across individual cathode sense resistors, and do a precision rectification of each signal, and compare the DC levels through each PP valve. For large signal levels, this may be a good indicator of the DC biasing actually being experienced by the OT (compared with just matching at idle level).

A current transducer that can meassure DC at low levels may also be able to measure such imbalance - eg. by passing both anode leads antiphase through the transducer (eg. a LEM, or tek current probe).

I guess another way could be to apply a dc current to an auxiliary winding on the OT (eg. use a separate secondary if available, or wind a separate turn or two if accessible), and then check if output distortion is minimised with bias.
  Reply With Quote


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
pre-amp tubes: matching and care jadzuke Tubes / Valves 6 23rd January 2010 03:41 PM
Matching tubes pot in old Fenders slideman82 Instruments and Amps 2 27th October 2009 03:06 PM
Matching tubes- WE 396a/RFT EL34 graykeene Tubes / Valves 1 21st August 2007 11:22 PM
12b4 as PP output tubes andyjevans Tubes / Valves 3 7th January 2005 08:50 AM
simple matching philosophy on tubes.. GeirW Tubes / Valves 1 17th February 2004 07:20 AM

New To Site? Need Help?

All times are GMT. The time now is 11:41 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2