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 2010, 04:07 AM   #21
jrn77478 is offline jrn77478  United States
diyAudio Member
 
Join Date: Jun 2008
Again, guys, many thanks for your assistance. No hurry at all George. This evening's trouble-shooting was interrupted by a call from work, so you have my complete understanding when it comes to work demands.

As I said, I've been through every connection and solder joint. No, no over-sized cap leads "requiring" drilling out the thru-holes.

The input connections, from the jack, through the pot (attenuator, actually), and to the board all check out OK. But taking the pot out of the circuit is on my list of hail Mary's.

I'll try swapping out OPT's. Continuity is good on both primary and secondary, with about 126 ohm on the primary. Sound about right? Anyway, I suppose something could have failed subtly and only shows up in operation.

That leaves the speaker jacks. The plate they're mounted on is metal, so I suppose a shorted hot is possible.

Failing those things, I'll set up for George's channel-jumping procedure. Probably won't have time for that until the weekend.

Last edited by jrn77478; 29th April 2010 at 04:12 AM. Reason: typo
  Reply With Quote
Old 29th April 2010, 03:03 PM   #22
Tubelab_com is offline Tubelab_com  United States
diyAudio Member
 
Tubelab_com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
I'll try swapping out OPT's. Continuity is good on both primary and secondary, with about 126 ohm on the primary. Sound about right? Anyway, I suppose something could have failed subtly and only shows up in operation.
I suppose anything is possible, but I have never seen it happen. 126 ohms is a realistic number, and if both OPT's measure within 10% of each other, they are probably OK.

Quote:
That leaves the speaker jacks. The plate they're mounted on is metal, so I suppose a shorted hot is possible.
There was a builder in England who had a dead channel. It turned out to be a short in one of the speaker jacks. Took a while to find it because it was pretty far down on the "likely suspects" list. How to test for it? Unsolder the OPT wires from the jacks and connect them directly to a speaker with clip leads. It is also possible to create a short if the cathode feedback connections are used, but one channel has the leads swapped at the PC board.

Is the dead channel completely dead, or is there some faint sound coming out? Often you need to disconnect the input from the good channel to be able to hear it.

Another simple test. Connect a junk speaker to the dead channel. Remove the output tube from the good channel (we want to kill that channel and you should never run a tube amp without a speaker). Connect no input to the amp and turn the volume control all the way down. Turn the amp on and allow it to warm up for about a minute, but do not let the tubes get too hot to touch, or swipe an oven mitt from the kitchen. With the amp on and running pull the 12AT7 from the socket. You should hear at least a loud pop, and probably some scratching sounds as the tube is wiggled. If so the output stage and speaker wiring is OK. If there is no sound at all pull the output tube. Again there should be a pop. If none the problem has to be in the OPT / speaker jack connection. Unplug the amp and allow 5 minutes for every thing to discharge before replacing the tubes.
__________________
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
  Reply With Quote
Old 30th April 2010, 01:09 PM   #23
jrn77478 is offline jrn77478  United States
diyAudio Member
 
Join Date: Jun 2008
Fixed.
Swapping OPT's led to the discovery of the failed component, though it wasn't an OPT. I'd decided to work my way in from the back of the amp. So I swapped secondary connections from R to L and L to R. The right speaker came up, plain as day. Left channel is clearly good all the way to... the binding posts.

The hot binding post on the left channel was open. Not shorted, open. The shaft that passes through the insulated barrel was snapped right in two (they were cheap), but the ends were apparently in close enough proximity that the force of my test probe (in my first pass of troubleshooting) would close it at least long enough for my brain to say, "There. The meter beeped. You've got continuity so let's move on to what's really wrong". The lightweight wires hanging off the post wouldn't torque it enough to do the same thing.

Thinking back, the only thing I can come up with is that I snapped the post while moving the amp to change tubes the morning it stopped working (unlikely - seems like I would have noticed something that forceful) or I just jostled it enough to pull it apart.

Anyway, thank you, everyone, for your generous input.
  Reply With Quote
Old 30th April 2010, 04:15 PM   #24
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
Glad you figured it out!
  Reply With Quote

Reply


SSE left channel dead....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
Can I have the sub woofer channel and the left and right channel as one? Boscoe Chip Amps 7 21st February 2010 06:56 PM
Dead Left Channel on my Kenwood CI Pre-amp bulgin Analog Line Level 0 22nd September 2009 02:33 AM
Class AB amp - left channel completely dead. Please help! Kolloi Solid State 4 15th December 2007 12:12 AM
Car Battery Dead...left the lights on... TomWaits Everything Else 10 11th January 2007 02:29 AM
DH-220 left channel dead rfarn Solid State 8 12th May 2006 12:35 AM


New To Site? Need Help?

All times are GMT. The time now is 07:20 PM.


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