Power tube filament issues - need help! - diyAudio
Go Back   Home > Forums > Commercial Sector > Vendor Forums > Tubelab

Tubelab Discussion and support of Tubelab products, prototypes and experiments

Reply
 
Thread Tools Search this Thread
Old 13th September 2011, 01:08 AM   #1
diyAudio Member
 
Join Date: Sep 2011
Default Power tube filament issues - need help!

Good day folks out there,

I am completing my Tubelab SE with 300B and I am having a weird problem. Without the power tubes (300B), I can read 5volts for both filaments. When I insert tubes, everything works for one or two minutes and then filament power shot down. I turn off the amp for a few minutes (until B+ and B- go down to 0volt), then I power up again and everything works for one and two minutes and shot down again, etc. etc.

B+ and B- remain OK (B+ = 415V and B- = 295V).

When I don`t put any power tube, filament voltage stays on forever, well I less 15 minutes.

I tried 50ma on tubes, same result with a lot of distortion. With 60ma, distortion seems to be gone but I have no scope to validate.

Any suggestions where to look at?

Alain

Last edited by Bola; 13th September 2011 at 01:09 AM. Reason: Typo
  Reply With Quote
Old 13th September 2011, 01:13 AM   #2
evanc is offline evanc  United States
diyAudio Member
 
Join Date: Sep 2009
Location: New Jersey. About 1 hour from NYC and 1 min. from the beach
maybe the filament regulator is overheating.
try blowing a fan at it and see if it stays powered up longer....
__________________
http://www.evancotler.com
  Reply With Quote
Old 13th September 2011, 01:16 AM   #3
rknize is offline rknize  United States
diyAudio Member
 
rknize's Avatar
 
Join Date: Feb 2009
Location: Chicagoland
Send a message via AIM to rknize Send a message via Yahoo to rknize
Yup....pretty common problem with the stock heat sink in the 300B configuration (the instructions mention this). The amp was originally designed for 45s.
  Reply With Quote
Old 13th September 2011, 01:17 AM   #4
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
It sounds like the voltage regulator for the 5 V filament supply is going into thermal shutdown. Try with a larger heat sink.

~Tom
  Reply With Quote
Old 13th September 2011, 01:20 AM   #5
diyAudio Member
 
Join Date: Sep 2011
It seems to be a concensus. I also read the same from a different blog. I am going to try to cold it down with a fan.

I confirm I only have the stock heatsink - no add on.
  Reply With Quote
Old 13th September 2011, 01:22 AM   #6
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Here's another thing to try: Pull one of the 300B's and operate the amp as a mono amplifier for a while. It should take longer for the regulator to reach thermal shutdown then.

The idle/quiescent current of the 300B has no impact on when the regulator goes into shutdown.

~Tom
  Reply With Quote
Old 13th September 2011, 01:54 AM   #7
diyAudio Member
 
Join Date: Sep 2011
You are all correct. With a fan on the IC, everything is back to normal.

I will add a better heatsick like George is recommending.

Thanks everybody for the quick help!

Alain

Last edited by Bola; 13th September 2011 at 01:56 AM. Reason: Typo
  Reply With Quote
Old 13th September 2011, 02:34 AM   #8
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
I will add a better heatsick like George is recommending.
Yes, depending on the ambient temperature and the airflow around the amp it can sometimes even shut down with 45's. The Lexan amp I made is about the worst possible case. The case is too small, there is no airflow, the power transformer is too small so it gets too hot to touch. On a hot day I had it shut off with 45's using the little heat sink. I added the big green one seen in the pictures and it will run all day with 300B's. It was borrowed from an old Pentium 1 motherboard.

That amp lost a power transformer in its first year, but autopsy revealed water damage due to hurricane forced water intrusion because I left the amp near a windowduring the storm. Yes, the window was closed. The replacement transformer has been in the amp for 6 years. It gets too hot, but doesn't blow up.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 14th September 2011, 11:48 AM   #9
diyAudio Member
 
Join Date: Sep 2011
Quote:
Originally Posted by tubelab.com View Post
Yes, depending on the ambient temperature and the airflow around the amp it can sometimes even shut down with 45's. The Lexan amp I made is about the worst possible case. The case is too small, there is no airflow, the power transformer is too small so it gets too hot to touch. On a hot day I had it shut off with 45's using the little heat sink. I added the big green one seen in the pictures and it will run all day with 300B's. It was borrowed from an old Pentium 1 motherboard.

That amp lost a power transformer in its first year, but autopsy revealed water damage due to hurricane forced water intrusion because I left the amp near a windowduring the storm. Yes, the window was closed. The replacement transformer has been in the amp for 6 years. It gets too hot, but doesn't blow up.
George,

As a note, my board was not mounted in a chassis yet. I conclude that the IC is probably not well mounted on the heatsink. Anyway, I have larger heatsink that I plan to install this week end.

Thanks for the advice.

Alain
  Reply With Quote
Old 14th September 2011, 05:00 PM   #10
rknize is offline rknize  United States
diyAudio Member
 
rknize's Avatar
 
Join Date: Feb 2009
Location: Chicagoland
Send a message via AIM to rknize Send a message via Yahoo to rknize
My TSE is also just sitting on a bread board. With 45s, convection was enough to keep it working (but it was still very hot). With 300Bs, I got 10 or 15 minutes of playing before it gave out. I clamped an aluminum "squangle" to the heatsink to get it to stay happy until I re-did the bread board.
  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
Any issues with adding a grounded power cord to a Heathkit IT-17 tube tester? BoilermakerFan Tubes / Valves 2 27th June 2010 08:34 PM
Weird old power transformers (filament, SS and tube) - $7 each! pjanda1 Swap Meet 6 29th March 2010 05:17 PM
Standard tube filament voltages and currents ilimzn Tubes / Valves 5 4th January 2010 06:53 AM
Tubelab SE input tube filament Evenharmonics Tubes / Valves 3 25th January 2009 01:10 AM
Tube-amp power issues Klimon Tubes / Valves 8 18th December 2006 09:29 PM


New To Site? Need Help?

All times are GMT. The time now is 06:36 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