Re: Poor student DIY toroid output xfos

GLM,

Are you sure you really want to use a toroid OPT? They are more prone to
core saturation problems than EI trannies. I've seen a fair number of
toroid PP iron but not many SE models.

Plitron is a leading manufacturer, also in Canada, but are well beyond your
budget. Nonetheless, you might learn something useful from them:

http://www.plitron.com/audio_se.asp and especially

http://www.plitron.com/audio_articles.asp

I have a pair of 40 W Hyboer SE (EI, not toroid) transformers, made for the
EL34 (3K impedance, IIRC). The only "drawback" is that they have several
output side taps . . . too many for my liking, but they are certainly
versatile. A good fit for your project?

Maybe I'll stick 'em on eBay and see what happens.

Jon





On 11/29/07 3:18 PM, in article 08F3j.13029$qP4.6959@xxxxxxxxxxxxxxxxxxx,
"GLM" <labbe-morissette.guillaume@xxxxxxxxxxxxxxxx> wrote:

Hi,

I'm a 3rd year uni student and I've completed my first complete tube amp
design up to the output stages. I've chosen my output tube (EL34 as SE
pentode), and most of the parts and got a nice preamp/tone control module up
and working. Now I'm at the point where I need to consider output
transformers...I've designed most of the amp according to the parts and
tubes I could easily get my hands on (budget constraints), summing at about
35$ per channel [God bless surplus Sovtek tubes] (doing it mono 1st, once
proven it'll go stereo :P) NOT INCLUDING the xfo. Looking at the price for
40W transfos, my jawbone is dropping at the prices (70$USD including
shipping is WAY out of question).

I'm not unexperienced to winding transformers with critical impedences and
turn ratios [did a few RF baluns and xfo secondary-voltage-divider-based
PSUs], and I still have my material at home and I have access to cheap
enameled copper wire, so the idea of winding them myself obviously came
right to me. Reading across previous posts on this forum, I came across the
toroids OPT thread. Winding toroids is a daisy so this sounds like the most
interesting option. However, being of very experience in the tube field,
I'm a bit sceptical about the overall size of a decent toroid able to drive
40W in 8 ohm speakers (although the self-shielding property does take a bit
off the xfo casing's size and complexity).

What topology would you recommend to use? Seperate windings on opposite core
sides or 2-layer winding around the core? I'm also not used to computing
core saturation issues with AF and such high inductances (RF obviously
requires so much less).

NOTE TO SELF-SUFFICIENT BLOATERS [you know who you are]:
Being a student, I do not have access to expensive materials. The main
idea of the project was to learn to design with tubes, not to build a tube
monster that would amplify a fly's fart to 90dB with 0.00001% THD. I loved
my experience with tube design and would like to get a nice sound off the
tiny amp I built. I'd love references to design litterature or comments
based on experience and technical parameters (core
inductance,inductance/impendence ratios, etc). Brand plug-in ["Get a
Lundahl, they sound great, Hammond makes decent ones too"], or strictly
qualitative comments about amp design other than output transformers ["PP
outputs are much better sounding"] are only a proof of how desperate you are
of finding a discussion where people are not yet annoyed of hearing your
obvious lack of reading skills and general comprehension for anything that
is not related to your personal issues and positions.

Thanks in advance,

GLM


.

Relevant Pages

  • Re: Smps Toroids on a Ground Plane
    ... Could I blanket my toroid with some foil and ground the foil? ... contained in the core. ... high dv/dt node at one end and a lower dv/dt node at the other. ... Placement of the high dv/dt pinshould be away from potential EMI ...
    (sci.electronics.design)
  • Re: Smps Toroids on a Ground Plane
    ... Could I blanket my toroid with some foil and ground the foil? ... contained in the core. ... high dv/dt node at one end and a lower dv/dt node at the other. ... Now I switch to that special winding technique.. ...
    (sci.electronics.design)
  • Re: Toroids for power transformers
    ... with NO LOAD. ... If the transformer has much inductance and low hysterisis ... If one buys a toroid with all the usual horrid problems most of them ... from the core. ...
    (rec.audio.tubes)
  • Re: interesting OPT winding comments
    ... The winding of a typical OPT with toroidal core means thousands of turns ... In practice it is not worth considering the normal toroid as an OPT. ...
    (rec.audio.tubes)
  • Re: Smps Toroids on a Ground Plane
    ... All the copper windings are too far from the ground plane.. ... Could I blanket my toroid with some foil and ground the foil? ... contained in the core. ... I don't know much about electric field interference. ...
    (sci.electronics.design)