DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 17 Oct 2018, 05:50

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 3 posts ] 
Author Message
 Post subject: Two Lessons Learned
PostPosted: 25 Sep 2018, 14:42 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3814
Location: Arizona, USA
Hi Everyone, A recent set of posts on the Oddblock thread has inspired me to pass along a few things that were discovered that might just prevent someone from have some really odd things go on in these amps and indeed others. First the tabs on the LM317s and many other similar power ICs are not ground connections. For the LM317 and particularly most TO-220 chips the tab is the output terminal. Grounding it will cause grief. :down: The IC will most likely be immediately destroyed and possible damage to the equipment. You must use the insulator wafers and feed throughs or insulate the heat sink entirely from the ground. Second, the anodized coatings on many things, including heat sinks is a pretty good insulator. In the instance that occurred the LM317 was mounted directly on the heat sink and the heat sink was fastened to the chassis. Surprisingly the amp worked for a long time. So the second concept is that if a component needs to be grounded and is finished in an anodized coating, you need to scrape some off to make a good connection.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Two Lessons Learned
PostPosted: 15 Oct 2018, 20:04 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 204
I've learnt a lesson in the past, using the tab and heat sink to conduct electiricty is a very bad idea, had a plorbem where lm317 have 7.5v output and lm337 had like varrying output from 6-7.3v
Solution was directly soldering wires to pins instead of relying on tab to heat sink electircal connection


Top
 Profile  
 
 Post subject: Re: Two Lessons Learned
PostPosted: 16 Oct 2018, 14:42 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 677
:) ,

Yes its a bit like soldering LM317T onto Vero board and forgetting to break the tracks between the legs of the device and the nut on the pin holding the heatsink so the whole thing shorts out..LOL

I always fit 2 mica insulators with compound between the insulators and tab / heatsink on high voltages.

Also watch out for the almost invisibly small piece of aluminium swarf bridging from the heatsink to the tab that gets stuck to the compound.
Make a point of doing a resistance test with a multi-meter from tab to heatsink as soon as you mount the device even before soldering the legs. It can save hours of work later.
I never trust the plastic insulator pads I have had a few fail in the past. But each to their own.
Here is another check the mounting pin to tab resistance as well.

In reference to the swarf under the pad and the resistance of anodizing is it can seem ok at first but the heating and cooling causes the pad or anodizing to break through some time later causing a burn out. Another is the type of head on the screw that goes through the plastic insulating spacer through the tab<<<it can cause the spacer to distort and split.
Another is if the screw rusts it can cause the tab to short. Not that its something I have to sort out..
NB the pin also has a heat transfer function..Just a thought.

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 16 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy