NTC THERMISTOR as SOFT START for TUBES - Page 4 - 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 7th June 2011, 11:47 PM   #31
SF1 is offline SF1  United States
diyAudio Member
 
Join Date: Feb 2011
Take precautions with these inrush current limiters, especially if you're experimenting. They explode suddenly like firecrackers throwing pieces around, and let out a terrible stink and smoke...

I had a CL-80 blow for no known reason. I replaced it and it's been fine for a year. Lesson is that I use goggles when I'm working with an open chassis that has an inrush current limiter that's exposed.
  Reply With Quote
Old 8th June 2011, 12:21 AM   #32
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Some commercial equipment put a sleeve of heatshrink over NTC and MOV devices. Typically this is for safety compliance, as the device package is not an insulator, but it also has the benefit of constraining debris from any rapid failure event.
  Reply With Quote
Old 8th June 2011, 06:31 AM   #33
diyAudio Member
 
Join Date: Jun 2008
A few years ago many people were recommending the same part # for various applications - CL-90 I think it was - from Thermometrics. - but specifying a NTC Thermistor should be done by calculation. Otherwise it's like saying "I wear size nine shoes, you should get some."

These guys make good ones and have a good website. Their engineer has helped me on the phone a few times and taught me some good stuff in the process.
  Reply With Quote
Old 9th June 2011, 03:31 AM   #34
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Bravo Hearingspace - First sensible post I've ever seen on Inrush Current Limiters on any of the forums I follow.

NTC Inrush Current Limiting Thermistors are NOT a case of one size fits all but must be selected on average steady state current draw.

When cold they have high resistance which suppresses the inrush current. When hot they have negligable resistance. If not specifed correctly they either don't get hot enough to reduce their resistance enough or they fail from getting way too hot.

There will always be one particular part which suits the particular application.

Here is another application note:
http://www.epcos.com/web/generator/W...ationnotes.pdf

I've used them a lot in the day job to supress peak currents at switch on in aircraft.

If (when the correct device is chosen) they still don't give enough inrush current suppressiion then I've used 2 (of the same rating) in series.

You can NOT use them in parallel. One device will heat up faster than the other and then hog all the current (till it expires and then the other will take over and expire in sympathy).

Cheers,
Ian
  Reply With Quote
Old 9th June 2011, 05:35 AM   #35
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Quote:
Originally Posted by SF1 View Post
Take precautions with these inrush current limiters, especially if you're experimenting. They explode suddenly like firecrackers throwing pieces around, and let out a terrible stink and smoke...

I had a CL-80 blow for no known reason. I replaced it and it's been fine for a year. Lesson is that I use goggles when I'm working with an open chassis that has an inrush current limiter that's exposed.
That's the reason to use equipment with a metal chassis in a wooden house like mine. MOV's may be UL registered but a wild gash can set alight to the dust and this is exactly what happened in another case where I had to waste a costly CO2 extinguisher putting out the fire.. I avoid these devices like the plague.


richy
  Reply With Quote
Old 9th June 2011, 05:53 AM   #36
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Here is mine: 12.6V rectifier and stabilizer for filament, 12V relay, and 20 Ohm wirewound resistor. Never blows up in peaces. The PCB contains also -80V bias rectifier.

Click the image to open in full size.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 18th December 2011, 07:06 PM   #37
roline is offline roline  United States
diyAudio Member
 
roline's Avatar
 
Join Date: Sep 2010
Location: East Tennessee
I use CL80's in all applications. Also started to use Damper diodes to soft switch the B+ from the first cap to the rest of the B+ filter chain. It allows for slow start for a slow ramp up of the B+ without the high peak and dip as the outputs come on line. It works great!
__________________
SO many tubes, SO little time!!!
  Reply With Quote
Old 31st December 2012, 12:48 PM   #38
diyAudio Member
 
Join Date: Oct 2011
Location: Close to Copenhagen
Quote:
Originally Posted by Yvesm View Post
This happens here too !
Use a self excited relay so that power is not reapplied before YOU decide

Yves.
Hi,
You got a point there, but what do you think about this circuit:

https://picasaweb.google.com/vbkolse...27848470641250

...would like to try this on my TVA-1 on: TUBEAMP The original inrush limiter is burned.

regards
  Reply With Quote
Old 6th February 2013, 11:54 PM   #39
diyAudio Member
 
Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
I've been debating this for my tube bass guitar amp too, which already has a 'standby' switch.

I'd like to use a make-then-break relay. One set of normally-open contacts would short across the NTC thermistors on the B+ when the relay is activated. That would make it cool in normal use, and always ready to limit inrush and have decent protection as long as the drain resistors drain down the filter caps at a slower rate than the cooling of the thermistors. Another contact set would connect the B+ supply to the amplifier load, like the standby switch origianlly did. The make-then-break relay would be wired to self-latch then disconnect the closed toggle switch so I would not have to use a momentary switch or pushbutton so that I would not change the appearance or basic operation of the amp and could keep the original stock toggle. But a dangerous power interrution and restoration would break open the self-latch and cause it to revert to standby mode with the thermistor back in-circuit; the user would have to turn the standby toggle switch off then on again to re-latch and play.

Last edited by cyclecamper; 6th February 2013 at 11:58 PM.
  Reply With Quote
Old 7th February 2013, 02:36 PM   #40
diyAudio Member
 
Join Date: Oct 2011
Location: Close to Copenhagen
Quote:
Originally Posted by cyclecamper View Post
I've been debating this for my tube bass guitar amp too, which already has a 'standby' switch.

I'd like to use a make-then-break relay. One set of normally-open contacts would short across the NTC thermistors on the B+ when the relay is activated. That would make it cool in normal use, and always ready to limit inrush and have decent protection as long as the drain resistors drain down the filter caps at a slower rate than the cooling of the thermistors. Another contact set would connect the B+ supply to the amplifier load, like the standby switch origianlly did. The make-then-break relay would be wired to self-latch then disconnect the closed toggle switch so I would not have to use a momentary switch or pushbutton so that I would not change the appearance or basic operation of the amp and could keep the original stock toggle. But a dangerous power interrution and restoration would break open the self-latch and cause it to revert to standby mode with the thermistor back in-circuit; the user would have to turn the standby toggle switch off then on again to re-latch and play.
Yes ..understand...to avoid the constant heat of the inrush limiter by use of a high voltage relay across the limiter.
If you can accept a small change of the bass amp function?:
If we look at the relay as automatical B+ protection guard, what should deactivate the relay, and let the inrush limiter take over.....too much voltage (mA) across the cathode resistor of the output tubes? ....say ...200mA before break?
Do you have the limiter partnumber/name?
This should be possible to calculate.
In the circuit I use for transistor DC amplifiers the threshold value is +-8Vdc. I shall ask my genius friend tonight of a simple circuit that takes care of the issue....then you only need one on-off contact switch for your bass guitar amp and one red/green double led to tell you go or no-go.
I have thought about this circuit for the TVA-1 KT88 amp, which at the same time tells you something about the remaining lifetime of your tubes...older tubes "runs" with the bias.

.....just a thought
  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
if an NTC thermistor is rated... jarthel Parts 2 21st May 2007 12:06 AM
how to select an ntc thermistor? jarthel Parts 7 2nd April 2007 10:00 PM
help with ntc thermistor jarthel Parts 4 1st October 2006 04:57 PM
Thermistor vs Soft Start argofanatic Parts 12 22nd September 2005 12:46 PM


New To Site? Need Help?

All times are GMT. The time now is 05:45 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