Tube Amp Squeel - 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 14th March 2012, 08:01 PM   #1
diyAudio Member
 
Join Date: Feb 2011
Default Tube Amp Squeel

I just finished building the S-5 Electronics K-16LS tube amp kit. It is in an aluminum chassis with Edcor CXPP30 output transformers. The problem is that as soon as the tubes warm up a high pitched squealing sound starts. This happens at every volume level, including zero volume. I have isolated the squealing to the preamp stage, since pulling the preamp tubes causes the squeal to stop. I have heard that this could be microphonics, but it seems strange that the preamp tubes for both channels would have this problem at the same time. I have tried tapping the preamp tubes, but this doesn't seem to change the sound, so I am not sure if microphonics is the problem. If anybody has any idea what might be wrong, I would be grateful for the help. Thanks.
  Reply With Quote
Old 14th March 2012, 08:39 PM   #2
diyAudio Member
 
Soonerorlater's Avatar
 
Join Date: Jul 2008
Location: Belfast
Quote:
Edcor CXPP30 output transformers.
Check your Output Transformer wiring to see if you have taken " positive " feedback off the OT secondarys instead of " negative " feedback.


Brgds Bill


ps, here is a link to ( I hope ) your amp schematic


Using Seperate Preamp to Drive S-5 Electronics K-16LS Integrated Amp?

Other thoughts,

1) According to the above schematic the negative feedback needs to be taken from the 4 ohm tap

2) Looks like the output transformer frame needs to be grounded
__________________
When white moths were on the wing,
And moth-like stars were flickering out,

Last edited by Soonerorlater; 14th March 2012 at 09:07 PM. Reason: schematic
  Reply With Quote
Old 14th March 2012, 08:42 PM   #3
diyAudio Member
 
Join Date: Jan 2008
Hello Jsine,

It could well be due to the amplifier's feedback being positive and not negative. To test for this try disconnecting the feeback loop and see if the problem goes away. If the amplifier has global feedback from the output transformer to the input stage and the squeel goes away when the feedback is disconnected. The problem was due to positive feedback and can be fixed one way or the other based upon the amplifier's design. Mickeystan

PS. Same perspective as Soonorlater posted. We must have been typing at the same time.

Last edited by Mickeystan; 14th March 2012 at 08:45 PM.
  Reply With Quote
Old 15th March 2012, 10:16 PM   #4
diyAudio Member
 
Join Date: Feb 2011
The squeal is gone. I reversed the plate leads on the output transformer primary and the squealing stopped. The PCB has the wire colors for the output transformers printed on the board, so I just hooked up my OPTs the way the originals were connected.
  Reply With Quote
Old 15th March 2012, 10:51 PM   #5
diyAudio Member
 
Soonerorlater's Avatar
 
Join Date: Jul 2008
Location: Belfast
Enjoy
__________________
When white moths were on the wing,
And moth-like stars were flickering out,
  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
my 250 watt tube amp can be a 500 watt tube amp for less than 2 bucks plus tubes speakerfritz Tubes / Valves 17 24th October 2013 11:50 PM
Amplifier squeel at zero volume AmpBuilder225 Tubes / Valves 4 11th July 2009 06:03 PM
FA: Eico HF-85 Tube Preamp & HFT-90 Tube Tuner joe-electro Swap Meet 0 31st May 2009 04:14 PM
FS tube tuner, Active filter kit, tube amp, amp3 Josephjcole Swap Meet 9 20th July 2007 04:05 PM


New To Site? Need Help?

All times are GMT. The time now is 03:51 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