Delay B+ using relay? - Page 2 - 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 17th January 2012, 04:39 PM   #11
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
I agree with payitforwardeddie. KISS.

However there are always extremists in any field.

During my Borbelly build #2 I made a few OVERKILL assumptions.

1. Valves are expensive and rare and should be treated with kid gloves.

If you think about the heater being just a low power light bulb. Most light bulbs fail when you turn them ON, they do fail in use but not as often.

In order to prolong their life it MIGHT be a good idea to turn them on SLOWLY and let them heat up SLOWLY.

2. Valves fail when they run out of electrons to donate from their cathodes.

OK - In HIGH POWER use it is beneficial to ensure that the valve is HOT before trying to draw current through it. This MIGHT prevent COLD STRIPPING of the cathode.

Both of these measures are largely immaterial in low power audio use and definitely OVERKILL in my Borbelly Pre-Amp.

But hey, I'm trying to preserve the few valves that are left in this world. I let the valves warm up for 30 secs and then apply B++

It's subjective. A good valve in a poor circuit will outlast a poor valve in an excellent circuit. I just wanted to give the amp a hint of being reliable for at least a few months without needing a tube change.
  Reply With Quote
Old 17th January 2012, 05:38 PM   #12
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
I once did the same: stabilized filament voltage, with current limit slowly going up. And B+ stabilized, with time constant sensing current consumption. When tubes started consuming current B+ went up faster. As the result, it brought up B+ slowly, waiting for tubes to start consuming current.

Now I limit inrush currents of all rectifiers at once by resistor in primary of power transformer. It is enough to sense one of rectified voltages, because they all go up proportionally to each other. Then relay shunts the resistor in series with primary.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 17th January 2012, 11:40 PM   #13
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
Quote:
Originally Posted by ryuji View Post
Im a little bit worried about my filter capacitors too tho, there rated for 500v but i imagine 10 or so seconds at up to 565v isnt going to internally heat them enough to kill them
I don't think heat is the issue here. I wouldn't recommend going that high in over-voltage, as you may experience capacitor failure, and you may have times when you go even higher due to mains variation. You may also run in to reforming problems if you don't use the amp for an extended period.
  Reply With Quote
Old 17th January 2012, 11:56 PM   #14
ryuji is offline ryuji  United States
diyAudio Member
 
Join Date: Feb 2011
Location: massachusetts
Quote:
Originally Posted by trobbins View Post
I don't think heat is the issue here. I wouldn't recommend going that high in over-voltage, as you may experience capacitor failure, and you may have times when you go even higher due to mains variation. You may also run in to reforming problems if you don't use the amp for an extended period.
so my initial worry and reason for wanting to implement the delayed b+ is at least somewhat valid, the b+ doesnt go past 450v when the tubes are conducting
  Reply With Quote
Old 18th January 2012, 02:31 PM   #15
ryuji is offline ryuji  United States
diyAudio Member
 
Join Date: Feb 2011
Location: massachusetts
i measured the startup super cold watching my first capacitor stage, it only reaches 530v and then as soon as hits 530 it drops fairly quickly. Dont think im concerned.
  Reply With Quote
Old 20th January 2012, 09:06 PM   #16
Account disabled at member's request
 
Join Date: Jul 2009
I am ignorant with tubes but here is what I gathered from my reading.

a. filaments must be hot when high positive DC comes on. When using rectifiers this is mandatory to avoid damage

b. in pentodes (full pentode mode) the screen voltage must not come on before b+ as the delicate grid will try to aborb the entire electron stream and fail.

c. bias voltage must ideally come on istantly to avoid damage

My future configuration for a PP amp based on the GU81m tube is:

LV (filaments) : switch ---> slow start ----> full power
HV (anode ecc) : switch ----> timer delay (5 minutes for my large rectifier) ----> softsart -----> full power

Sounds complex but really only three modules are needed and all should go well.
  Reply With Quote
Old 20th January 2012, 09:22 PM   #17
diyAudio Member
 
Globulator's Avatar
 
Join Date: Aug 2004
Location: Cambridge, England.
Quote:
Originally Posted by Wavebourn View Post
Now I limit inrush currents of all rectifiers at once by resistor in primary of power transformer. It is enough to sense one of rectified voltages, because they all go up proportionally to each other. Then relay shunts the resistor in series with primary.
This sounds the best idea to me, what type of values and times do you use for a particular power draw? I.e. what values (R and t) would you use for a typical 40W push-pull stereo amp>
  Reply With Quote
Old 6th March 2012, 11:59 PM   #18
diyAudio Member
 
Join Date: Mar 2012
Quote:
Originally Posted by Alexontherocks View Post
I am ignorant with tubes but here is what I gathered from my reading.

a. filaments must be hot when high positive DC comes on. When using rectifiers this is mandatory to avoid damage
Not for lower anode voltage tubes, or lower current tubes, and not for directly heated tubes. If you have 2000 volt or higher tubes with indirectly heated oxide cathodes, and the tubes run a fair amount of current, it starts to be a worry. The higher the anode voltage and cathode current in oxide cathode tubes, the greater the worry.

Quote:
b. in pentodes (full pentode mode) the screen voltage must not come on before b+ as the delicate grid will try to aborb the entire electron stream and fail.
Depends on the screen circuitry and the screen's allowable dissipation over time. Maybe it will hurt, maybe not. Depends on the screen system and tube.

Quote:
c. bias voltage must ideally come on istantly to avoid damage
Right, for tubes that overdissipate without bias we want bias before or at the time anode and screen voltages appear.

Quote:
My future configuration for a PP amp based on the GU81m tube is:

LV (filaments) : switch ---> slow start ----> full power
HV (anode ecc) : switch ----> timer delay (5 minutes for my large rectifier) ----> softsart -----> full power

Sounds complex but really only three modules are needed and all should go well.
People tend to lift little snips of truth from one application and apply it to other systems without the faintest idea why things are the way they are.

Directly heated tubes suffer no ill effects when HV applied before the filament power is applied. It is also doubtful you will ever see inrush damage to the tube filament on that tube.

Oxide cathode emitters, when very high voltages are used, tend to flash over if HV is applied at low cathode temperatures. Oxide cathodes also, if emission current density is high, tend to hot spot when very high currents are drawn before the cathode is fully warm. What this does is heat the already hotter parts of the cathode. There is also a problem of positive ion poisoning if the electron cloud is stripped away, with higher voltage tubes.

This is why lower voltage low current oxide cathode tubes, like 4CX150's, have a short "recommended" (but not required) holdoff time requirement, while high voltage hogh current tubes like 3CX10000B7's have a mandantory 5 minute heater time before HV is applied. Receiving tubes normally have no requirement at all to hold off voltage.

Thoriated tungsten tubes have none of the problems oxide cathode tubes do.

Delayed HV with warm up of small low voltage tubes just gives people something to feel special about, unless they have design errors they are patching (like unstable HV supplies that soar to unsafe levels before the tubes draw current).
  Reply With Quote
Old 11th March 2012, 11:40 AM   #19
Account disabled at member's request
 
Join Date: Jul 2009
Very informative reply. Thanks. However my ignorant approach is actually the most conservative. Aside from the fact i have power station level rectifiers which need at least 5 minutes to warm up any other design issue will find a solution in an overly cautious approach. Also there is a distinct setling time for the gu81m filaments. The entire tube makes the oddest sounds and vibrations before the metal parts expand and set in place. I'd rather give this time to the tubes before putting them in operation.

Inviato dal mio GT-I5800 usando Tapatalk
  Reply With Quote
Old 11th March 2012, 03:20 PM   #20
Account disabled at member's request
 
Join Date: Jul 2009
I had to cut the message short typing from my cell phone. I simply wanted to point out that in any given case 30 seconds warmup and softstart for the HV is not something that most people can't live with. It gives time for the filaments to properly warmup, it can help the user to identify problems with tubes (ie: bad socket tube contact, damaged filaments etc) I know it sounds unlikely but I really can't see what's wrong with allowing 15-30 seconds of warmup before HV comes on.
With gas rectifiers this is mandatory thus setting the main question of whether the output tubes benefit from it aside.


Also I don't see what's special in having a relay start....what is there to brag about? It is a small delay switch or even a small timer delay tube. Nothing exotic.
  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
B+ time delay relay cbutterworth Tubes / Valves 24 31st August 2011 12:53 PM
Delay relay Alkis Tubes / Valves 5 30th November 2009 06:56 AM
Relay delay Ted205 Chip Amps 16 24th September 2008 05:44 PM
Delay-Off relay peace brainerd Parts 7 12th May 2007 03:14 AM
Time Delay Relay Tubes cadman Tubes / Valves 8 17th December 2002 04:25 AM


New To Site? Need Help?

All times are GMT. The time now is 05:13 PM.


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