Go Back   Home > Forums > > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubelab Discussion and support of Tubelab products, prototypes and experiments

Reply
 
Thread Tools Search this Thread
Old 29th April 2016, 05:05 PM   #11
Guarnera is offline Guarnera  United States
diyAudio Member
 
Join Date: Feb 2010
Location: S.California
Hey w5jag,
The Mundorf Poly Tube Caps are Big polypropylene Caps designed for Tube power supplies. The Clarity Cap is a standard for electronics Capacitor.
I've tried different rectifier tubes. Still Drifts.
I have a fan inside the unit, and the drift is slower when the fan is on. So I'm pretty sure its a thermal problem with a part. I've ordered a new cap for C4 position, since C4 value effects the voltage.
By the bleeder resistor do you mean the resistor from the B+ rail to ground (R30) ? If so I will try that next.
Thank you for all the help.
  Reply With Quote
Old 29th April 2016, 07:54 PM   #12
w5jag is offline w5jag  United States
diyAudio Member
 
Join Date: Feb 2007
Location: Arkansas
Do you have another DMM? If so, try it and see if you are seeing the same pattern of drift.

It's a possibility, remote perhaps, that your meter is drifiting, but might as well eliminate that before you start changing parts.

Win W5JAG
  Reply With Quote
Old 30th April 2016, 01:51 PM   #13
Guarnera is offline Guarnera  United States
diyAudio Member
 
Join Date: Feb 2010
Location: S.California
Quote:
Originally Posted by w5jag View Post
Do you have another DMM? If so, try it and see if you are seeing the same pattern of drift.

It's a possibility, remote perhaps, that your meter is drifiting, but might as well eliminate that before you start changing parts.

Win W5JAG


Changed DMM. Same Drift. Started at 379 volts. After 10 hrs. of play it dropped to 369 volts, with the fan running.
  Reply With Quote
Old 1st May 2016, 11:54 PM   #14
Guarnera is offline Guarnera  United States
diyAudio Member
 
Join Date: Feb 2010
Location: S.California
I'm still studying what's going on. But I'm starting to think that The downward drift of the Bias current of the 300B tubes corresponds to the downward drift of the B+ voltage. Seems like after 4,or 5 hours, with the fan on the B+ settles at around 370 volts. I say the because it will bounce between 370 and 371. Sometimes after a few more hours it sometimes drops to 369 volts. But when it's settled and bouncing between 370 volts and 371 volts, the bias current stops dropping also and bounces between 68 ma and 682ma. So I think as the B+ drops it brings the Bias current down also.
Any ideas as to what to look for? I have a replacement coming for C4. I'll keep my fingers crossed. Thank you all.
  Reply With Quote
Old 4th May 2016, 01:23 PM   #15
Guarnera is offline Guarnera  United States
diyAudio Member
 
Join Date: Feb 2010
Location: S.California
Default Tale of two meters!

I have 6 DMM's. Two good Flukes, and 4 cheap flee bay meters. I had one of the cheapo meters on the AC line voltage in my shop, which is a small steel building, powered by an extension cord from the garage. It read 120 Volts steady. So I figured it was the same in the garage, where I have the amp and speakers playing now, to break in the tubes. Well, that meter craped out on me so it got retired. I took one of my flukes and put it on the AC line voltage.
I have a 8.2uf cap in the C4 position. And it seems my line voltage is high. It starts out in the mornings at about 123 volts, and slowly declines all day to 121 volts at night.
So it seems like when its cold and the AC is 123 volts it starts out with about 379 to 380 volts B+. As it warms up it seems like the voltage drops faster then the AC drops. After about 30 min or so it has dropped to about 375 volts B+. Then it seems to follow the AC voltage. The AC voltage drop isn't a straight linear decline. As it drops over the day it fluctuates up and down, but gets lower as the day goes on. The B+ volts follows the AC voltage up and down.
It seems about .3 volts change in the AC voltage equals a 1 volt change in B+ voltage. At about 10 PM yesterday she was at about 122 volts AC, and about 369 volts B+.
So my conclusion is that when cold the B+ is a little high. As it warms up that corrects it self, and then the B+ follows the AC line voltage decline. So I think its working as it should. I can't hear any change in the sound as the voltage changes. I'm only talking about a 1 to 2 volt change in the AC voltage. So I think I'm good to go.
  Reply With Quote
Old 21st May 2016, 09:41 PM   #16
Guarnera is offline Guarnera  United States
diyAudio Member
 
Join Date: Feb 2010
Location: S.California
The drift was mostly AC line voltage changing, but also it seemed to drop faster the first 20 minutes. I was using a Sovtek 5AR4 rectifier tube. I changed that to a NOS Mullard 4 notch 5AR4/GZ34 tube and the voltage drop as the tube warms up stopped or is a lot less. It seems to just follow the AC voltage now.
  Reply With Quote
Old 3rd June 2016, 08:23 PM   #17
bermtoog is offline bermtoog
diyAudio Member
 
bermtoog's Avatar
 
Join Date: Apr 2011
Location: Atlanta, GA
Quote:
Originally Posted by Guarnera View Post
The drift was mostly AC line voltage changing, but also it seemed to drop faster the first 20 minutes. I was using a Sovtek 5AR4 rectifier tube. I changed that to a NOS Mullard 4 notch 5AR4/GZ34 tube and the voltage drop as the tube warms up stopped or is a lot less. It seems to just follow the AC voltage now.
My 300B TSE has been doing the exact same thing. It starts out at about 379ish and as it warms up over thirty minutes to an hour, it gets to about 368. My guess is it has to do with the silicon somewhere.

Also, for those saying that tubes don't drift a pretty good bit in the first few hours, I don't where you're getting your tubes, but mine varied considerably for at least the first 5-10 hours. I've finally got them dialed in now and the bias rises to the same point and the two 300B's seem to stay pretty even. But in the beginning, they drifted up to 10-20mA.
  Reply With Quote

Reply


B+ voltage drift?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Oscilloscope X-Y Drift ragwire Everything Else 2 5th December 2015 12:35 PM
BOZ voltage drift GregH2 Pass Labs 0 21st March 2012 02:10 PM
Bias Drift AmpBuilder225 Tubes / Valves 9 4th November 2009 04:38 PM
DC offset drift BBB Pass Labs 5 20th December 2002 04:42 PM
Drift of MOSFET source voltage namui Solid State 1 5th February 2001 12:00 PM


New To Site? Need Help?

All times are GMT. The time now is 01:25 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki