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

EL34 output transformer replacement
EL34 output transformer replacement
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 12th January 2018, 02:53 AM   #1
samitha10555 is offline samitha10555
diyAudio Member
 
Join Date: Sep 2010
Default EL34 output transformer replacement

Hi, recently an damaged output transformer was rewound and reinstalled in my Muse EL 34 based amplifier. Now there is a motorboating noise coming from the channel that the transformer was repaired. Further it was noted that this noise goes off when the Negative feedback loop is removed.
Much appreciate if I could get advise to sort out this issue.
Many thanks
  Reply With Quote
Old 12th January 2018, 05:19 AM   #2
VaNarn is offline VaNarn  Australia
diyAudio Member
 
Join Date: Dec 2010
Location: Ivanhoe
EL34 output transformer replacement
If you can swap the O/P transformers over, the process may indicate if the fault is with the rewound transformer or it is specific to the one channel. Swapping the tubes/valves over may also be a worthwhile procedure to follow as a faulty one could be the cause of the problem. I trust that the transformer rewinder carefully followed the 'recipe' of how the original sectioning of the primary and secondary wirings were layered. If not you have an expensive repair on your hands.
  Reply With Quote
Old 12th January 2018, 06:11 AM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
EL34 output transformer replacement
May be as simple as the plate/screen leads are swapped. Assuming that power supply decoupling is in order (and not shared between channels) it could be swapped leads or the transformer has more LF phase shift than was originally case and this is particularly critical if the design is based on the Williamson.
__________________
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
  Reply With Quote
Old 12th January 2018, 06:13 AM   #4
samitha10555 is offline samitha10555
diyAudio Member
 
Join Date: Sep 2010
Thanks VaNArn, I did swap the two transformers and now fault has got transferred. As you mentioned looks as if there is an issue with the re-wound transformer but all works fine when negative feedback loop is removed. No distortions. Sounds good but volume level has gone up as a effect of NFB removal. Is there a way to adjust the NFB to suit the rewound transformer?
  Reply With Quote
Old 12th January 2018, 06:18 AM   #5
samitha10555 is offline samitha10555
diyAudio Member
 
Join Date: Sep 2010
Thanks KEvin, Yes as you said could be that transformer has more LF phase shift but how could we explain what is happening when NFB is removed?
  Reply With Quote
Old 12th January 2018, 07:15 AM   #6
petertub is offline petertub  Sweden
diyAudio Member
 
Join Date: Jul 2015
Location: gothenburg,sweden
There might be excessive large caps in the amp. Transmitting and amplifying frequency's outside the transformers ability is a sure way to get feedback problems.

As the problems occurs after rewinding, the rewinding have not reproduced the transformer as it was. A repeated rewind might be a waste om money, i would buy a new transformer from some well-known source.
__________________
My home is at www.tubular-well.se
  Reply With Quote
Old 12th January 2018, 09:55 AM   #7
samitha10555 is offline samitha10555
diyAudio Member
 
Join Date: Sep 2010
Thanks petertub
  Reply With Quote
Old 12th January 2018, 10:13 AM   #8
bandol83 is offline bandol83  France
diyAudio Member
 
Join Date: Nov 2004
Location: near Bandol, French Riviera
I would check if the negative feedback is connected correctly since the problem disappear when it is removed ! It is possible that the signal and ground lines are crossed...

Please check before to buy another transformer
  Reply With Quote
Old 12th January 2018, 10:18 AM   #9
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
Swap the anode load leads over to invert the NFB phase.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 12th January 2018, 11:21 AM   #10
wdecho is offline wdecho  United States
diyAudio Member
 
Join Date: Oct 2014
EL34 output transformer replacement
Had same problem with Chinese kit. Swap plate and B+ wires. An example my wires were blue and red. I put red to B+ and blue to plate and it oscillated with feedback. I reversed the wires, blue to B+ and red to plates and cured the problem.
  Reply With Quote

Reply


EL34 output transformer replacementHide 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
el34 output transformer, 3 or 5 wire ~? nigelwright7557 Instruments and Amps 18 25th June 2013 06:05 PM
SE and PP Output Transformer for 300B, KT66, EL34, 6P6P siliconray Siliconray Online Electronics Store 6 17th November 2011 01:46 AM
Output transformer for PP EL34 source pof@ Tubes / Valves 7 22nd May 2010 09:09 AM
How do I tell whether a different replacement output transformer will be ok? digitallake Tubes / Valves 6 4th June 2009 09:51 PM
Output transformer replacement... Worth it? apehead Tubes / Valves 9 20th July 2008 02:26 PM


New To Site? Need Help?

All times are GMT. The time now is 10:00 AM.


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