Designing an Interstage 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 28th February 2013, 03:46 AM   #1
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Default Designing an Interstage Transformer

I wish to design and construct an interstage transformer for an SET amplifier using a 6A5 or 6B4G.

Driving tube will be a 6N7 with both plates in parallel for an effective RP of around 5500R.

Max bias current will be 10mA.

I just finished reading chapter 5 of RDH4, and plan on re-reading it. I've also been reading other works about transformers in general.

I'm probably going to have a lot of questions, but will try to go through the design process.

The cores I have are stripped from a set of24W line matching transformers. The laminates weigh 556gr per set.

The cores are loss-less EI cores with an I measurement of 1.122cm X 6.692cm by .45mm thick.

Tongue width is 2.23cm
Stack height is 2.57cm
Window is 1.05cm by 3.0cm (with the bobbin I made installed)

The cores are probably marginal for the project, however I have them so I plan on using them for a first iteration design.

estimated MLP 15.35cm
estimated MTL 14.021cm

Step 1. Calculate required inductance based on minimum frequency response and the driving tube plate resistance and drive voltage to the grid of the output tube (35Vrms).

Rp=5500R
F1=10Hz (yea, aggressive)

Use Xl=5* Rp = 5* 5500R =27500

Xl=2* PI * 20 * L
L = XL/(2 * PI * 10)
L = 27500/(2 * PI * 10) = 218 H

This is the first problem. It may be necessary to abandon the 6N7 for the 6SN7 with an Rp of 3850 for parallel plates, which would cut the inductance requirement to 152H.


So, is this correct so far?
  Reply With Quote
Old 28th February 2013, 04:35 AM   #2
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Oops.

That is 6A3, not 6A5.
  Reply With Quote
Old 28th February 2013, 05:45 AM   #3
jcdrisc is offline jcdrisc  Australia
diyAudio Member
 
Join Date: Jun 2011
To get reasonable bandwidth and phase response you will have to segment the windings.
Homegrown audio transformers are usually low quality and are rarely worth the effort.
Better to go to Jensen or Sowter and buy a guaranteed product.
  Reply With Quote
Old 28th February 2013, 01:29 PM   #4
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
It is VERY difficult to make an IT with that high inductance that isn't anything than a muddler. (It will have horrible high frequency response and muddle your sound).
However I don't believe winding ITs and OTs is such a mytical black art as so many claim. The trick is having the proper tools, such as a winder of some sort that lets you wind with proper tension and that lets you lay the wire nicely along the bobbin. Doing a few transformers you can probably get decent tension simply by hand feeding, but for how many turns?...

Interleaving and winding layers to be with as low capacitance as possible isn't easy, but doable. You'll need patience to run some test windings if you only want the best. I don't think the cheaper manufacturers like EDCOR does much fancy interleaving and other techniques in their transformers.

I think for one you really need to relax your specs. Why 5xRp? 10Hz as low end goal is admireable, but is there really that much to gain in happiness? Better to aim for 20 or even 30Hz and get better wide band response IMHO.

Anyway, hope you give it a try. I've just bought some left over amorphous cores for same idea, interstage trannies, but will use lower Rp tubes like 6922 and trioded 6W6s. I think you core size is plenty for this useage. As you know you need some air gap since it'll be SE, and that'll require even more turns to make the Henrys. Good luck.

Oh, what size wire are you using?
  Reply With Quote
Old 28th February 2013, 02:18 PM   #5
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Buy it.
Expensive? ..... Who cares?
SE systems are for people with fat wallets anyway.
  Reply With Quote
Old 28th February 2013, 02:20 PM   #6
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
But this is diy isn't it? If any one here does diy to save money I think they picked the wrong hobby.
  Reply With Quote
Old 28th February 2013, 02:30 PM   #7
diyAudio Member
 
the_manta's Avatar
 
Join Date: Nov 2006
Location: Munich, Bavaria
Quote:
Originally Posted by SemperFi View Post
The trick is having the proper tools, such as a winder of some sort that lets you wind with proper tension and that lets you lay the wire nicely along the bobbin. Doing a few transformers you can probably get decent tension simply by hand feeding, but for how many turns?...
IMHO the trick is experience and knowledge. Winding machine, proper laminations and wire can be bought. But the technique to get the lowest stray capacitance is based on experience and skill.
__________________
Терпенье и труд все перетрут
  Reply With Quote
Old 28th February 2013, 02:50 PM   #8
sjs is offline sjs  United Kingdom
diyAudio Member
 
Join Date: Oct 2011
Location: Manchester
I have to say you are starting with probably the most difficult audio trans to wind imho.

For good performance from interstage driver transformers, bi-filar windings are by far and away the best method to get good bandwidth, but you will need high quality double insulated wire, and v good winding technique to reduce risk of primary to secondary breakdown.

I would suggest your best bet is to buy commercial from Hammond, Audio Note or Monolith Magnetics.
Best of luck
  Reply With Quote
Old 28th February 2013, 03:00 PM   #9
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
he, a few months ago I began to construct my own amp box handles
basicly because I thougt the were way too expencive
and sometimes too much work to find the right one

scrapped some, but have had my share of fun doing it
and I can now make one in no time

but learning how to wind a trafo probably takes a bit longer
  Reply With Quote
Old 28th February 2013, 03:51 PM   #10
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Remember that you need to calculate the windings to be just a kiss undersize, because of you can's fit the bobbin into the lamination window you are sunk.

Please take lots of photos of your progress, I know most of us will like to see the process!!!
  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
Reversing Interstage Transformer HP8903B Tubes / Valves 19 10th May 2012 05:36 AM
Interstage Transformer Questions galac Tubes / Valves 6 30th July 2011 05:54 PM
Inverted Interstage Transformer NickC Tubes / Valves 4 6th January 2011 12:57 AM
Is this a good interstage transformer? m6tt Tubes / Valves 3 5th January 2011 11:14 PM
interstage transformer effindi Tubes / Valves 8 10th November 2009 01:51 PM


New To Site? Need Help?

All times are GMT. The time now is 06:52 AM.


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