Placement of Ultralinear Tap On Homemade Transformer - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st March 2008, 08:43 PM   #1
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Default Placement of Ultralinear Tap On Homemade Transformer

I'm seriously contemplating winding some SE transformer for a couple of big projects. Though both of the projects I'm considering are triode-based so that the tap is not an issue, I'm wondering how to place the ultralinear tap with an interleaved construction fpr optimal coupling. Placement at 50% is a no-brainer, but what about 40% or other arrangements?
  Reply With Quote
Old 31st March 2008, 09:13 PM   #2
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
It also depends on which valve you're going to use. There was a thread recently that discussed ultra-linear taps in depth...
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 31st March 2008, 09:27 PM   #3
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Well, I wasn't worrying so much about which percentage of tap to use, but where physically to put the tap in the winding structure, which is another matter altogether.
  Reply With Quote
Old 1st April 2008, 02:09 AM   #4
diyAudio Member
 
MQracing's Avatar
 
Join Date: Oct 2005
Quote:
Originally posted by wrenchone
Well, I wasn't worrying so much about which percentage of tap to use, but where physically to put the tap in the winding structure, which is another matter altogether.
A conventional practice of good workmanship in making transformers is to place any taps at the end of a layer---

if you pull a tap from say the middle of a layer--- your going to have to wind over the wire exiting and re-entering that layer--- to the spot where the tap was pulled. This puts some mechanical stress on the wire--- and to prevent shorts these leads exiting and re-entering the layer are typically covered with some insulation to protect them electrically as well--- the achilles heel of this approach is that it also leads to increased leakage inductance.

So--- it is generally considered best (unless there would be some vastly overriding requirement) to pull any taps at the beginning or end of a layer.

Hope this helps,

MSL
  Reply With Quote
Old 1st April 2008, 03:10 AM   #5
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Crossover insulation is not so much of a problem in terms of increased leakage when the wire in question is smaller than 30 AWG. One could also use tape with 1 mil (0.025 mm) thickness for crossover duty without unduly compromising the insulation.
The point may be moot, as the primary sections will have to be multiple layers to accomodate the required number of turns to satisfy requirements for sufficient primary inductance and bias current capability. I'll have a wide range of tap options by pulling a tap off of one of the intermediate layers.

I was looking at a EI 1 1/8" lamination, with a 1.5" thick stack (standard bobbin). For a transformer with 150 mA peak capability and 50 H inductance, this comes out to about 5000 primary turns. I will have to review what other transformer makers offer in that size, as I was going by the rule of thumb of making the primary impedance to equal the load impedance at 20Hz.
  Reply With Quote
Old 1st April 2008, 10:21 AM   #6
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by wrenchone
rule of thumb of making the primary impedance to equal the load impedance at 20Hz.
You might want to give that rule of thumb some thought. What you're effectively saying is that at 20Hz the reactance of the transformer's primary inductance draws the same current as the load current, but in quadrature. Or, to put it another way, the output stage has to supply 1.414 times as much current. That will increase the distortion of the output valves. Further, the increased current in the transformer takes you closer to saturation, and at saturation, there is no primary inductance. All in all, you need to be very careful as you approach saturation.

Now, you're in the position of knowing what your load (loudspeaker) is. If it's a bookshelf loudspeaker, it's probably a closed box with a resonant frequency of 60-80Hz. If so, its impedance at 20Hz is going to be quite close to the DC resistance of the voice coil and all of the previous considerations apply. On the other hand, if your loudspeaker is a big reflex, it might have its port tuned to 30Hz, making the impedance at 20Hz quite a bit higher than the DC resistance of the voice coil, and leaving the load on the output valves at 20Hz simply the output transformer primary inductance.

So, if you've got a big reflex box, then your rule of thumb is probably fine, but you might want to rethink if you have a small closed box.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 1st April 2008, 10:51 AM   #7
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
Hi EC8010,

Can't beleive your are suggesting that we must target a larger primary inductance because small loudspeakers are unable to correctly load the amp (nor providing any sound at lowest frequencies)

What about a lo cut somewhere, preferably before the OPT

Happy April 1st.

Yves.
  Reply With Quote
Old 1st April 2008, 11:37 AM   #8
Serge66 is offline Serge66  Switzerland
diyAudio Member
 
Serge66's Avatar
 
Join Date: Nov 2007
Location: Canton of Jura
Somewhere between 40 and 50%, at the end of a primary section.
You are interleaving the windings, aren't you?
__________________
"I have a bag, therefore I like am, like I exist, like..." says the bimbo with the Louis Von bag.
  Reply With Quote
Old 1st April 2008, 12:40 PM   #9
diyAudio Member
 
Join Date: Jul 2003
Location: Ann Arbor, MI
hey-Hey!!!,
You can put in more than one tap too. Go for ~20% and around 40%. The end-of-layer placement is a good idea, and exactly where your taps go will depend on how many layers you have to build. With 5k turns, I suspect you'll have more than 10 layers so the increment will be at most 10%.
cheers,
Douglas
__________________
the Tnuctipun will return
  Reply With Quote
Old 1st April 2008, 12:55 PM   #10
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by Yvesm
Can't believe your are suggesting that we must target a larger primary inductance because small loudspeakers are unable to correctly load the amp (nor providing any sound at lowest frequencies)

What about a low cut somewhere, preferably before the OPT

Happy April 1st.
Hello Yves, I take your point that it seems a contradiction to need more primary inductance for a loudspeaker that's unable to reproduce the frequencies where that primary inductance matters, but think about it, as we enter saturation, we generate third harmonics, and the little loudspeaker is certainly capable of reproducing them. On the other hand, perhaps that will give an illusion of bass from shoebox loudspeakers.

I would certainly prefer to see a high pass filter so that the amplifier only has to cope with signals that it and the loudspeaker can handle, but that's probably heresy.

If I'd realised it was April 1st, I would have come up with something even more surprising. Still, look at it another way, largish reflex loudspeakers will work better than you would expect with a given primary inductance. I'd always felt that reflex loudspeakers suited valve amplifiers very well, and had previously assumed it was simply due to their highish output resistance, but it could also be the kinder loading at low frequencies.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  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
which one is Correct EI Transformer placement ?? dytln_02 Power Supplies 4 6th July 2008 09:39 AM
Ultralinear pse mark_titano Tubes / Valves 1 5th November 2007 11:54 PM
Homemade magnets and homemade magnetizer jacquesl The Lounge 0 19th February 2007 07:32 AM
Transformer Placement 5E3 gtrbryan Tubes / Valves 2 6th November 2006 02:51 PM
PP-1c as Ultralinear Charles BL Tubes / Valves 1 28th January 2003 04:52 AM


New To Site? Need Help?

All times are GMT. The time now is 11:43 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