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 11 Dec 2018, 07:43

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 5 posts ] 
Author Message
 Post subject: Valve heater flash..
PostPosted: 14 Jun 2017, 11:44 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 677
Yes the forever nuisance,

This is project specific but worth a mention.
I have a few Telefunken and Amperex tubes that flash at power up due to heater current surge.
Now if its harmful or not is not the point..I just don't like it.. :P

So I thought I would post for interest I wanted a quick work around while using AC heater supply.
So the question was how to get an inrush limiter to work with the low current of the driver tube..

Of course this is a pointless question the current isn't enough to operate the limiter and the resistance has to be high enough to give the voltage drop with inrush current. :confused:

Of course that's the wrong question..the answer is put the limiter in line with the power tubes and driver tube. Then the power tubes operate the limiter and the driver tube just tags along for the ride. No more flash.

Obviously the current and value needs to be worked out, however it works. Also in my case I thought it wouldn't work with changes in power tube due to current change. OK you get a slight drop in heater voltage at working point, but I have ideas around slight changes in heater voltage point..thats a different topic.

NB a side issue of this is the inrush surge at power up reduced, obvious with heaters drawing so much current but again worth mentioning.
I wasn't going to post this but someone may find it interesting.
Anywhere where you get heater delay there are other factors like B+ rails max voltage and any direct coupling but this (hopefully)should already be sorted in the design.

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
 Post subject: Re: Valve heater flash..
PostPosted: 14 Jun 2017, 17:09 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3853
Location: Arizona, USA
Hi, I'm not sure I have an answer for that. But it did start a thought train. :idea: It would seem that any tubes of the same type would have a fairly consistent ratio of hot resistance to cold resistance. The flash would only depend on the visibility of the heater. Thus I wonder if most tubes do this but we don't see it because the cathode covers them up more. It is definitely a brand and production run related issue. On the positive side, I'm not sure it is a good thing...but then it may not be a bad thing. I have nearly had zero tubes fail in the umpteen years I have been fiddling with them due to heater failure. The best way I can see around it is with a CCS. To use one though you will need to go to DC on the heaters. On the plus side some folks swear by current regulation though tubes (esp preamps) and claim all sorts of benefits. I seem to muddle through with voltage regulation. :|

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Valve heater flash..
PostPosted: 15 Jun 2017, 10:12 
Offline
User avatar

Joined: 05 Aug 2016, 14:35
Posts: 220
It has been my experience that some tubes, especially those that have not been used in a great while, will flash upon power-up. I have also found that after repeated use, the flashing reduces, and in some few cases goes away altogether. I have not always found this to be brand-specific, but Teles have figured in the mix.

Accordingly, I have come to the unsupported conclusion intuitively that the flash is related to inactivity. And that the flash is due to minute leaks at the base. Also unsupported.


Top
 Profile  
 
 Post subject: Re: Valve heater flash..
PostPosted: 15 Jun 2017, 14:20 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 677
just for interest,

Ref resistance under load.


Regards
M. Gregg


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
What is the sound of one hand clapping?


Top
 Profile  
 
 Post subject: Re: Valve heater flash..
PostPosted: 15 Jun 2017, 21:03 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
gofar99 wrote:
The best way I can see around it is with a CCS.


That's been my solution as well if the customer is adamant.

12AT7's are the "flashiest" ones, especially the EU ones.

Another method is use the tubes with the "A" suffix... 12AX7A, 12AT7A, etc. as the "A" means controlled warm-up.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Exabot [Bot], Google Adsense [Bot], Majestic-12 [Bot] and 18 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