Foolish Mistake - 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 22nd March 2013, 03:49 AM   #1
diyAudio Member
 
Join Date: Oct 2004
Default Foolish Mistake

Hello,
I had my Tubelab SE (300B) for more than 4 years without any problem. Tonight, I was setting the bias on the right channel via R18 (about 65ma) when my voltage meter lead slipped and a spark occurred. Right after, I cannot measure any current on R18 and no music is flowing on the right channel. I turned the amp off and switch tubes, I thought I killed my right channel 300B but after switching, still the right channel is dead with music on the left.

All tubes are glowing. R18 and R29 measured at 10 ohms. No music on right channel. Did I kill my right channel mosfet (Q1)? Thanks for helping.
  Reply With Quote
Old 22nd March 2013, 05:25 AM   #2
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
So you measure B+ on both sides of R18? What about the tube plate? Best to check just to verify that the OPT is OK. Aside from that, yeah it sounds like you may have killed R34 or the FET. You might also want to look carefully at the PCB traces. Take some measurements on both sides of R34 to see if the bias voltage is there and that it changes when you turn the pot.

Where was the probe when it slipped? Do you have clip leads?
  Reply With Quote
Old 22nd March 2013, 04:57 PM   #3
diyAudio Member
 
Join Date: Oct 2004
Thanks Russ. No, I don't have clipped leads. I think I touch the jumper. How do I check if the OPT is okay? Is there a way to check the FET? I'll measure voltages and post later. I am away from my home. Godspeed.

John Revilla
  Reply With Quote
Old 22nd March 2013, 06:12 PM   #4
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
The DRV_B+ jumper? Maybe it got shorted to R34. We'll know if the primary is open when you check the plate voltage at the tube socket. Be careful when probing around such high voltages without clip leads!
  Reply With Quote
Old 22nd March 2013, 06:22 PM   #5
diyAudio Member
 
Join Date: Oct 2004
Hi Russ,
Yes, the DRV jumper. I'll check R34. You mean the plate voltage for the 300B? I do have clipped leads but was just doing a quick adjust when it happened. Thanks. Godspeed.
  Reply With Quote
Old 22nd March 2013, 07:48 PM   #6
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
Yeah, if you have B+ on the plate of the 300B, you know your OPT is OK. it probably is, but you never know. Since you saw a big spark, I'm assuming the DRV jumper (with B+ on it) shorted to R34. If you shorted B+ to the FET side of R34, I wouldn't expect anything bad to happen unless the back-EMF killed the FET. So I'm left to wonder if the shock simply popped R34 itself.
  Reply With Quote
Old 22nd March 2013, 07:53 PM   #7
diyAudio Member
 
Join Date: Oct 2004
Thanks Russ,
I'll measure and report. Godspeed.

John Revilla
  Reply With Quote
Old 23rd March 2013, 07:08 AM   #8
diyAudio Member
 
Join Date: Oct 2004
Hi Russ,
Is the plate for the 300B tubes pin#3? I measured 390v on the left channel (working) but 0v on the right. R18 is dead. R34 is 100 ohms. How can I be sure that my opt (Electraprint) is not damage? Is there another way to test the opt? Thanks.
  Reply With Quote
Old 23rd March 2013, 05:40 PM   #9
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
Oh, OK...somehow I thought you already checked R18. If you see B+ on the other side of R18, the OPT is fine.
  Reply With Quote
Old 23rd March 2013, 08:16 PM   #10
diyAudio Member
 
Join Date: Oct 2004
Russ,
I change R18 and got B+ on the right side now. All voltage measurements plate, R18, R34) are the same as the left (good channel). I'll try with output tubes and see is music will flow. Godspeed.
  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
is a quality 'needle' on mediocre TT foolish for recording? 60ndown Analogue Source 21 3rd May 2011 05:47 AM
Where is mistake?? azazello Tubes / Valves 4 25th February 2011 02:22 PM
Help with a foolish question- technics se-m100 Jo90 Solid State 3 3rd November 2009 05:24 PM
foolish notion, 12GN7 model? billy pilgrim Tubes / Valves 1 26th February 2007 01:27 AM


New To Site? Need Help?

All times are GMT. The time now is 11:24 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