robomatique

Valve/Tube Safety & Bleeder resistors
« on: June 21, 2004, 09:05:11 PM »
Hello,

I am just about to start my first tube project, the G9, and I am a bit worried because I have never done any tube stuff before.

As I understand it, I should use a resistor to bleed off the capacitors to be sure there is no voltage left in the system. Could someone explain this in detail,? I really want to get this absolutely right and to be as safe as possible.

Somewhere I have seen a small 'bleeder board' that you can build to make everything easy to use when working. Anyone knows what I am talking about?

Robert
"Trying is the first step towards failure."
-H. Simpson


CJ

Valve/Tube Safety & Bleeder resistors
« Reply #1 on: June 21, 2004, 09:22:22 PM »
It is much better to install permanent bleeder resistors.
I  use 220 k 1 wat resistors on the first B+ cap.
Takes a while to discharge, check with your voltmeter to watch the resistor in action after pwr down to give you a realtime figure for discharge time.
cj
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Ethan

Valve/Tube Safety & Bleeder resistors
« Reply #2 on: June 21, 2004, 09:25:19 PM »
All you need is a resistor with long leads (I usually use a 1K 10W because I have a bunch lying around).  Or if you prefer you can attach insulated alligator clips to the leads.  Then connect one end to the positive lug of the cap and one end to the negative end.  Give it a minute to discharge (or longer depending on the value of the cap).  Your best bet is to always measure it with a voltmeter to make sure it still isn't holding any juice.

-E
I am just the Web Geek here.

gyraf

Valve/Tube Safety & Bleeder resistors
« Reply #3 on: June 22, 2004, 04:17:32 AM »
On my desk, I keep an extra voltmeter with the sole purpose of monitoring HT voltage on the current project. That allows for a quick overview of danger. A cheap digi-voltmeter is fine for this, I just mounted alligator-clips on it's wires.

When discharging, it's always a good idea to watch the voltage fall slowly. If you just measure when you think it should be discharged, you won't be really sure that your voltmeter behaves correctly..

Take care,

Jakob E.
..note to self: don't let Harman run your company..

rafafredd

Valve/Tube Safety & Bleeder resistors
« Reply #4 on: June 22, 2004, 09:55:32 AM »
Quote from: "gyraf"

When discharging, it's always a good idea to watch the voltage fall slowly. If you just measure when you think it should be discharged, you won't be really sure that your voltmeter behaves correctly..

Take care,

Jakob E.


DonĀ“t understand why... Can you tell me more, Jakob?

gyraf

Valve/Tube Safety & Bleeder resistors
« Reply #5 on: June 22, 2004, 10:13:07 AM »
..because this will also show you if your voltmeter is connected correctly, set and working right, and has proper battery power. I don't trust a single measurement that says "0V".

Watching the meter slowly go towards zero is a simple way of fail-safing all this.

Jakob E.
..note to self: don't let Harman run your company..

rafafredd

Valve/Tube Safety & Bleeder resistors
« Reply #6 on: June 22, 2004, 10:37:59 AM »
You are right. One can never be cautious enought.

kent

Valve/Tube Safety & Bleeder resistors
« Reply #7 on: June 22, 2004, 10:59:22 AM »
I soldered a big 'ol 100R 2W resistor to a test lead with an alligator clip on the end and shrinkwrapped the lot.  I attach the clip to ground and bleed the cap through the resistor tip.  I (almost  :?  ) always check with a meter to see if it's drained nicely.

cheers,
kent
I don't really know what I'm playing.  It's just a bunch of notes.

CJ

Valve/Tube Safety & Bleeder resistors
« Reply #8 on: June 22, 2004, 12:16:48 PM »
A permanent bleeder also helps regulation somewhat, or so my electronics teacher told me.
 :guinness:
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Eric H

Valve/Tube Safety & Bleeder resistors
« Reply #9 on: June 22, 2004, 01:05:24 PM »
Quote from: "Admin"
 Or if you prefer you can attach insulated alligator clips to the leads.  Then connect one end to the positive lug of the cap and one end to the negative end.  Give it a minute to discharge (or longer depending on the value of the cap).  Your best bet is to always measure it with a voltmeter to make sure it still isn't holding any juice.

-E

Yes, and leave it connected until you're finished --caps have a nasty habit of recharging themselves (another good reason for the permanent-bleeder).

-Eric


soundguy

Valve/Tube Safety & Bleeder resistors
« Reply #10 on: June 22, 2004, 01:31:10 PM »
can anyone provide a napkin drawing of how to correctly install a permanent bleeder resistor?

thanks

dave

chips are good with dip...

robomatique

Valve/Tube Safety & Bleeder resistors
« Reply #11 on: August 19, 2004, 09:13:11 PM »
Quote from: "soundguy"
can anyone provide a napkin drawing of how to correctly install a permanent bleeder resistor?

thanks

dave


Bumping this one, considering a permanent bleeder resistor on my G9
"Trying is the first step towards failure."
-H. Simpson

CJ

Valve/Tube Safety & Bleeder resistors
« Reply #12 on: August 19, 2004, 09:29:52 PM »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Aharon

Valve/Tube Safety & Bleeder resistors
« Reply #13 on: August 19, 2004, 10:39:04 PM »
And if you put a LED in series with the resistor you get a discharge indicator,no?.
Aharon
Just learning n' having fun

adamasd

Valve/Tube Safety & Bleeder resistors
« Reply #14 on: August 20, 2004, 01:13:32 AM »
I still use a screwdriver. Although I might finaly switch to a bleeder. Had an amp chassis sitting in my lab and my bare foot was touching it when shorted the cap to ground and my foot. That was a nice surprise.

adam
so there

kooma

Re: Valve/Tube Safety & Bleeder resistors
« Reply #15 on: October 28, 2014, 10:40:05 AM »
I know this is an old topic, but generally;

How do I select the right value for bleeder resistor?
are there any downsides of using something big ohmic values(besides long discharge time)?

0dbfs

Re: Valve/Tube Safety & Bleeder resistors
« Reply #16 on: October 28, 2014, 10:56:43 AM »
I still use a screwdriver. Although I might finaly switch to a bleeder. Had an amp chassis sitting in my lab and my bare foot was touching it when shorted the cap to ground and my foot. That was a nice surprise.

adam

A screwdriver? ??? ??? ???

I found out about this not-so-fun-trick when working on a tube guitar amp a number of years ago. The screwdriver shaft literally vaporized in a huge blue corona as I threw what was left across the room in an extreme fit of "WTF" way before wtf was in the popular vernacular.

In addition to vaporizing the tool it also burned this lesson permanently into my organic ram sticks which I hope can be passed along and save another life via preventative procedures.

For safety's sake please don't use a screwdriver to bleed the caps.... Use a high value bleeder resistor as recommended here. ie; 100k, 200k... And monitor the voltage in the cap with a meter like Jacob described.

Cheers!
-jonathan
Music is everything!
Audio is everything else!

ruffrecords

Re: Valve/Tube Safety & Bleeder resistors
« Reply #17 on: October 28, 2014, 01:47:27 PM »
I know this is an old topic, but generally;

How do I select the right value for bleeder resistor?
are there any downsides of using something big ohmic values(besides long discharge time)?

It is a trade off between speed of discharge and and wasting power. The bleed resistor is always there so it is like an additional load on your HT supply. If you design it for a quick discharge time it will consume more power than for  longer discharge time. Also, if you have some big electrolytics in the HT supply to get the ripple right down for a preamp for example, then these will take longer.

I used to use 270K on my 300V supplies so it wasted only 1mA when in use but it can take several minutes to discharge. I now use a heater elevation pot divider across the HT supply that adds 88K across in and so discharge much faster but it does waste  nearly 4mA.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

kooma

Re: Valve/Tube Safety & Bleeder resistors
« Reply #18 on: October 29, 2014, 02:28:42 AM »
I know this is an old topic, but generally;

How do I select the right value for bleeder resistor?
are there any downsides of using something big ohmic values(besides long discharge time)?

It is a trade off between speed of discharge and and wasting power. The bleed resistor is always there so it is like an additional load on your HT supply. If you design it for a quick discharge time it will consume more power than for  longer discharge time. Also, if you have some big electrolytics in the HT supply to get the ripple right down for a preamp for example, then these will take longer.

I used to use 270K on my 300V supplies so it wasted only 1mA when in use but it can take several minutes to discharge. I now use a heater elevation pot divider across the HT supply that adds 88K across in and so discharge much faster but it does waste  nearly 4mA.

Cheers

Ian

Ok, thanks!
So capacitance  doesnt matter much?
I've got some big-ass-caps for my tube heaters that got me searching for info:)
maybe I just juse something like 100K for HT and 5-10K for heaters.

CJ

Re: Valve/Tube Safety & Bleeder resistors
« Reply #19 on: October 29, 2014, 02:55:25 AM »
a bleeder does three things that i know of,

1-bleeds the caps for safety
2-improves regulation of the power supply
3-keeps excessive voltage off the caps during power up

tubes will not conduct til they warm up, if you use solid state rectifiers then there will be no delay of the B+ voltage due to a rectifier tube warming up, this means the caps will see excess voltage until the warm tubes drop this voltage by way of the resistance in the xfmr sec..

modern caps do not seem to mind a little over voltage for a few seconds,
but resistors are so cheap, so WTF, over?  ;D

« Last Edit: October 29, 2014, 03:01:24 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


 

Related Topics

  Subject / Started by Replies Last post
1 Replies
1185 Views
Last post March 04, 2010, 11:50:25 AM
by shabtek
20 Replies
3021 Views
Last post June 16, 2016, 04:23:52 PM
by Gene Pink
32 Replies
2917 Views
Last post September 21, 2018, 08:35:41 AM
by EmRR
29 Replies
2357 Views
Last post November 07, 2019, 08:19:57 PM
by Monte McGuire