*my* Tubelab SE build... - Page 11 - 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 7th July 2009, 11:30 PM   #101
diyAudio Member
 
oldmanStrat's Avatar
 
Join Date: Apr 2009
Ok, it's not the transformer.

I cut one leg of the rectifier heater windings - nothing.

Next I cut ONE leg of the 660 AC (T1-4)... powered it up and the fuse that I bought from the hardware store never went, but R5 did !! Nicely, sort of like a sparkler... a few days too late though.

R5? That's interesting. B- is drawing too much current. Why would it go with only one phase attached to it... Could be that the fuse I used was extra slo-blow.

I'd suspect the mosfet, but it didn't measure shorted and there is no B+ anyway.

I need ideas at this point...
__________________
For security reasons my name is changed daily...
  Reply With Quote
Old 7th July 2009, 11:48 PM   #102
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
R5? Maybe C6 is shorted?
  Reply With Quote
Old 7th July 2009, 11:56 PM   #103
diyAudio Member
 
oldmanStrat's Avatar
 
Join Date: Apr 2009
Quote:
Originally posted by rknize
R5? Maybe C6 is shorted?
Neither side of R5 measures a short to gnd. This is with power off... of course R5 now measures inf... probably have another one in my box of spares. But I'll just blow that one too until this is figured out.
__________________
For security reasons my name is changed daily...
  Reply With Quote
Old 8th July 2009, 12:03 AM   #104
arnoldc is offline arnoldc  Philippines
diyAudio Member
 
Join Date: Apr 2003
Location: Makati
Send a message via Yahoo to arnoldc
@oldmanstrat, hi have you isolated that it is not the power transformer? Did you check the transformer disconnected from the board?
  Reply With Quote
Old 8th July 2009, 01:23 AM   #105
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
Quote:
Originally posted by oldmanStrat


Neither side of R5 measures a short to gnd. This is with power off... of course R5 now measures inf... probably have another one in my box of spares. But I'll just blow that one too until this is figured out.
It just seems a little bizarre to me that R5 would blow and not R6. Perhaps R6 can handle the overload better.
  Reply With Quote
Old 8th July 2009, 01:37 AM   #106
diyAudio Member
 
oldmanStrat's Avatar
 
Join Date: Apr 2009
Quote:
Originally posted by arnoldc
@oldmanstrat, hi have you isolated that it is not the power transformer? Did you check the transformer disconnected from the board?
With both leads cut from the PCB there aren't any blown fuses or expensive fireworks. I also measured the 330-0-330 leads and they are within spec (670vac) disconnected from the board.
__________________
For security reasons my name is changed daily...
  Reply With Quote
Old 8th July 2009, 01:49 AM   #107
diyAudio Member
 
oldmanStrat's Avatar
 
Join Date: Apr 2009
Quote:
Originally posted by rknize


It just seems a little bizarre to me that R5 would blow and not R6. Perhaps R6 can handle the overload better.
I wondered that too. R6 is a 5W R5 is a 2W... so it would go first. This could be a case of debug induced problem without solving the real issue. But the problem of blowing fuses is gone... and R5 is pointing the way.

It's a stumper. Kinda like a brain quiz.
__________________
For security reasons my name is changed daily...
  Reply With Quote
Old 8th July 2009, 02:43 AM   #108
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
OK, so with R5 "gone" you can hook the transformer all back up to the PCB and it doesn't blow fuses? That's a good sign. While R5 is only a 2W part, it's only 270 ohms while the 5W part is 10k. So for a given current through the two, Ohm's law says R5 can handle about 4x the current that R6 can before reaching its dissipation limit. That was my line of thinking anyway. Can you check the resistance of R6 to see if it is still in spec? If it somehow shorted internally (pretty rare, but who knows), maybe it is passing much more current than it should.

If the power supply side checks-out, then yeah...the MOSFETs would be the next thing to look at. Maybe try desoldering one leg of R14 and R25 and then replace R5. If you can power up like that (no tubes, of course), then the MOSFETs are likely the culprit.

EDIT: the above might be such a good idea...maybe George can chime-in here but lifting those resistors might cause C6 and C7 to see too much voltage due to the drop in current draw on the B- rail. In this circuit, I measure about 200k between the source and the drain (pin 3 and 2). Put positive lead from yoru meter on the source.
  Reply With Quote
Old 8th July 2009, 02:53 AM   #109
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
R5 is there to limit peak diode current, which in turn reduces noise. I have found two ways to make it fry. Bad diodes D2 or D3 or bad caps C6 or C7. I would bet on the diodes.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 8th July 2009, 11:56 AM   #110
diyAudio Member
 
oldmanStrat's Avatar
 
Join Date: Apr 2009
Quote:
Originally posted by rknize
OK, so with R5 "gone" you can hook the transformer all back up to the PCB and it doesn't blow fuses?
I haven't hooked the transformer back up yet...

I would agree with you that it could be the mosfets, but since there is no B+ I just don't see a current path there...

Quote:
Bad diodes D2 or D3 or bad caps C6 or C7. I would bet on the diodes.
My meter says that they are both still diodes. Although one is dropping more than the other (.8v vrs .6v). The caps appear to be still caps, since there are no shorts.
__________________
For security reasons my name is changed daily...
  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
Tubelab SE build and power supply questions. Binaural Tubes / Valves 54 3rd March 2010 03:20 AM
Another TubeLab SimpleSE Build nic6paul Tubes / Valves 91 13th June 2009 03:16 AM
Nubie first build Tubelab simple SE Mungo Park Tubelab 65 27th May 2009 05:41 PM
Long time lurker - first build a tubelab Simple SE cjkpkg Tubelab 59 21st December 2008 05:54 PM
Newbie wants to build Tubelab SE Monos. audiobliss Tubes / Valves 12 19th July 2008 01:40 AM


New To Site? Need Help?

All times are GMT. The time now is 01:43 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