Oscillation in tube amps - Page 14 - 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
Reply
 
Thread Tools Search this Thread
Old 30th June 2016, 11:10 AM   #131
diyAudio Member
 
jhstewart9's Avatar
 
Join Date: Apr 2013
Location: near Toronto
Occasionally, to the surprise of the constructor the local friendly 50 KW AM broadcaster shows up in their carefully designed project.

What fun!!
  Reply With Quote
Old 2nd July 2016, 03:28 PM   #132
diyAudio Member
 
jhstewart9's Avatar
 
Join Date: Apr 2013
Location: near Toronto
If you use a device capable of 400 MHz, you DO have gain at 400 MHz, whether you want it or not.

I agree with this, unexpected parasitic circuits can & are a real problem to be aware of. Terman & others cover these in some detail for those of us willing to take the time to look.
  Reply With Quote
Old 4th July 2016, 02:50 AM   #133
diyAudio Member
 
Join Date: May 2005
Location: Pretoria, South Africa
Quote:
Originally Posted by jhstewart9 View Post
If you use a device capable of 400 MHz, you DO have gain at 400 MHz, whether you want it or not.

I agree with this, unexpected parasitic circuits can & are a real problem to be aware of. Terman & others cover these in some detail for those of us willing to take the time to look.
Please see my post #130; perhaps I worded it poorly.

One is well aware of the threat of parasitic oscillations; such awareness should be standard practice in all designs. But I consider the reference to 400MHz per sé misleading. Parasitic oscilations can occur at any (high) frequency, where a device as well as circuit elements are favourable to such.

Again: It may be considered as semantics, but devices are not capable of a certain frequency (per sé) although there is obviously a frequency limit for each. Circuit elements can cause unwanted oscillations whatever the device, etc. - I don't think we disagree, but it can be important to have the correct approach regarding this. For prevention one concentrates on the circuit and layout, the device is of secondary importance (in the right context, naturally).

Whichever way; if we both succeeded in emphasising the importance of possible parasitic oscillations, the purpose is served.
  Reply With Quote
Old 4th July 2016, 06:31 PM   #134
hpeter is offline hpeter  Slovakia
diyAudio Member
 
hpeter's Avatar
 
Join Date: Feb 2013
Location: Electrostats or bust
Audio tubes are not very steep, but when you use uhf mega steep tube.. You asking for trouble
__________________
BLOG. XMOS_U8/PCM5102A > LL1544A > 6H1Pi+µfoll > 2A3_SOV/JJ > LL1660 > STAX SR207 _ SR L300 _ SR007 # LL2748 > 394A > LCLC 4H/100µ
  Reply With Quote
Old 16th September 2016, 01:12 PM   #135
rmb is offline rmb  United States
diyAudio Member
 
Join Date: Nov 2012
Location: western PA
Defective electrolytic filter/decoupling capacitors will also cause oscillation or "motor boating"...

Electrolytic capacitors are best checked by substitution or wiring a good unit across the suspected cap. If the capacitor is shorted or leaky, the defective capacitor must be replaced.

The older multisection can capacitors can be tested by substitution. The older can capacitors are expensive or hard to find; either the entire cap has to be replaced if a defective section is found, or a suitable capacitor wired across the defective section if space is available. If any section of the multisection can capacitor is leaky, that section cannot remain connected.

If you cannot find a replacement for the original defective multisection can capacitor and want to preserve the integrity of the unit, CAREFULLY remove the capacitor as to not break the phenolic chassis mount. Then put on gloves, remove the bottom seal with the terminals carefully and save it, then remove the "innards" of the capacitor (goo, etc.) and save the can. Do not remove any internal grounding jumper from the can. Discard the "goo", etc.; then clean the can thoroughly, and install replacement capacitors inside the can, using insulating tubing to prevent shorts when reconnecting to the bottom seal terminals. The negative side of the capacitors is the can, so the can and the negative side of the replacement capacitors must be connected together, preferably at or as close as possible to the common negative terminal. Take your time and do not rush this.

WARNING - HIGH VOLTAGE - Make certain the unit is unplugged and the capacitors are discharged before working on the unit. The voltages used in tube equipment can be lethal!
  Reply With Quote
Old 19th October 2016, 03:19 PM   #136
diyAudio Member
 
Join Date: Oct 2016
Default Clicking Noise

As for clicking noises, I have found that many are caused by leaky caps resulting in what has also been called popcorn noise. It can sometimes be found by doing a simple dc resistance measurement across each cap... a leaky cap can show a relatively low resistance (<80kohms or so).
  Reply With Quote
Old 26th October 2016, 12:24 PM   #137
Monode is offline Monode  United Kingdom
diyAudio Member
 
Join Date: Jun 2011
Location: UK
Sometimes the junction between the leadout and a resistor or capacitor can add frequency specific distortion as well as acting as an RF aerial. I like the RF inductor on the output Tx secondary on page 1 of this thread, I might give that a go tonight!
  Reply With Quote
Old 2nd November 2016, 08:26 AM   #138
diyAudio Member
 
Join Date: Sep 2015
Default give em a push

Lead dress is a BIG issue....Iv'e found out the hard way but its helped me build lovely quiet amps...

motorboating and clicks.....sounds like caps....are you using new ?

Get a stick and push the wires around and see how they react while monitoring...you may discover a few sleepers laying around in loops

  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
For Sale: Tube Amps, Class-A Amps, BG Ribbons, Chassis and Other Goodies! opc Swap Meet 23 2nd November 2009 05:04 PM
Help Please with tube amps!!!!! bobcat1979 Instruments and Amps 1 28th June 2009 11:29 AM
Tube amps & MP3's jim Tubes / Valves 18 20th February 2008 04:15 AM
Tube Oscillation or Microphonic Question Trout Tubes / Valves 6 29th December 2005 04:18 AM


New To Site? Need Help?

All times are GMT. The time now is 06:49 AM.


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
Wiki