NEED calculation for Impedance matching transformer for vacuum tubes amp   - Page 1
Forum section: electronics / general

author: uranium235
author_rank: Contributor
timestamp: August 12, 2010, 10:22:43 am
content: does anyone know a link, book or any soure for making Impedance matching transformer for vacuum tubes ampim want to make one for my 15W tube amp project

author: djsb
author_rank: Super Contributor
timestamp: August 12, 2010, 10:38:17 am
content: Is this for the output stage or for interstage matching?David.

author: MTron
author_rank: Regular Contributor
timestamp: August 12, 2010, 12:25:35 pm
content: Hey uranium,Check out this site for some great info on tube amps, if you haven't alreadyhttp://diyaudioprojects.com/they have some great free plans available, and the people on the forums are quite knowledgeable.Now, as for your immediate issue, try looking up the data sheet for your power tubes, there should be a recommended range for the primary impedance for the output transformer, just remember to match the secondary impedance to the speakers your using as well.For curiosity sake, what tubes are you using, SE or PP output stage?Don't know if you read the thread, but i completed a Tube amp a few months ago using EL84 output tubes with a 5751 driver tube, you can see the project herehttps://www.eevblog.com/forum/index.php?topic=676.msg8050#msg8050

author: uranium235
author_rank: Contributor
timestamp: August 12, 2010, 06:51:59 pm
content: @ daveim using it in output stage@ MTronthanks for the linksim planning to use pp for output stageby the way nice tube amp project

author: MTron
author_rank: Regular Contributor
timestamp: August 16, 2010, 12:45:45 pm
content: What tubes are you using, might be able help you determine what output impedance u should runAlso, keep us updated...and pics!!!

author: uranium235
author_rank: Contributor
timestamp: August 19, 2010, 12:09:16 pm
content: @MTronim still on the planning stagehere is the diagram of the circuit that im planning to build and also my 1st tube amp projecthttp://1.bp.blogspot.com/_bXU7O6Ba3kg/SrZzon3i2vI/AAAAAAAAA2E/DdsHpEhJn2w/s1600-h/Tube+12AT7+%2B+6W6+Push+-+Pull+15WATT+P0WER+AMPLIFIER.gifim still researching more about tube ampsregarding on the circuit is it posible to replace 6w6 with EL84?

author: MTron
author_rank: Regular Contributor
timestamp: August 19, 2010, 06:38:55 pm
content: As a direct substitution, no i dont believe so. Im not very familiar with the 6W6, while the heaters will be fine, i believe the plate voltage rating is different, as well as bias current. Not to mention the 6w6 is a tetrode with an octal base, and the EL84 a pentode with a nonal base, but it is possible to wire a pentode tube as a triode, so with the correct changes to the plate resistors, you could sub in an EL84...i just dont know what those changes are ATMI have looked over that schematic, and i have a few suggestions. Firstly, i would substitute a solid state rectifier instead of the 5y3 rectifier tube, it will be more efficient, and will save you from having to heat another tube. The voltages from a SS rec will be about 10% higher, but it shouldn't be a problemI would also add some additional capacitance to the filtering stage just after the rectifier.If you also find that the amp is a bit noisy, u should consider DC heaters instead of AC, but only if you find it a problem.Now, truth be told, this project is a fair bit more complex them some of the ones hosted on DIY AudioProjects, so unless you have already started buying parts, i would suggest seriously looking at one of them.On another note, take a look at Edcore or Hammond output transformers, i personally use the Hammond 125D, and the 125 series is a universal OPT, so you can wire it up to have a very large range of primary and secondary impedance combinations. Edcore has similar projects. While Hammond's are VERY good quality, i would say the Edcores have the edge in the aesthetics category (equally good sounding for comparable trannies)

author: uranium235
author_rank: Contributor
timestamp: August 20, 2010, 11:26:03 am
content: currently on its planning stage i haven't bought the partsim still considering the availability of the components locally and costim really having a hard time on the matching transformer due to my location (southeast asia)so im thinking to make one rather than to buywhich make its much cheaper in addition the excess magnet wire could be used on other projectsany way thanks for the adivice

author: DJPhil
author_rank: Frequent Contributor
timestamp: August 20, 2010, 02:18:59 pm
content: Quote from: uranium235 on August 20, 2010, 11:26:03 amIf you do take the plunge and wind your own please stop back and tell how it goes! I've got an old tube signal generator's worth of parts (poor thing) and I've realized that I could build an amp, I'm only short preamp tubes and an output transformer. I'd love to read a good story on learning to make one!

author: rossmoffett
author_rank: Regular Contributor
timestamp: August 20, 2010, 11:39:36 pm
content: Winding an output transformer for a tube amp is no simple task. I haven't done it before, but I know from reading forums that you must interleave the windings to prevent losses. That means you don't wind one coil, then the next, and so on. Instead, you wind all coils at once, interleaving them with one another. I have seen websites covering the design issues for this before, but can't remember where. I found them through a web search or maybe an amplifier forum like ampage.org. Geofex.com has a lot of tube-amp specific stuff, maybe check there.Sourcing the EI laminates is another issue, I've still not found a source for small quantities of laminate material.I did hear of a guy at AX84.com winding a toroidal output transformer once, you might search the forum archives there or web search. He was pleased with his results. You can buy toroidal cores from a few places, the type you want for this application is a wound wire or wound ribbon type. Don't use a powder or ferrite core.

author: tecman
author_rank: Frequent Contributor
timestamp: August 21, 2010, 02:29:42 am
content: Quote from: MTron on August 19, 2010, 06:38:55 pmActually a 6W6 is apentode, not a tetrodepaul

author: uranium235
author_rank: Contributor
timestamp: August 21, 2010, 11:34:58 am
content: Quote from: rossmoffett on August 20, 2010, 11:39:36 pmdo you mean the EI is an laminated iron core?btwi found a site herehttp://europa.spaceports.com/~fishbake/ot1/ot.htm

author: tecman
author_rank: Frequent Contributor
timestamp: August 21, 2010, 12:00:17 pm
content: EI is type of core, made from iron materials. It is the basis of most "conventional" transformers. There are two pieces, ine looks like an E and the second like an I. The I goes across the end of the E to close the magnetic path. The laminations are alternated, typically every 1, 2 or 3 pieces. The coil is wound and placed over the middle of the E as it is laminated.paul

author: uranium235
author_rank: Contributor
timestamp: August 21, 2010, 02:33:01 pm
content: Quote from: tecman on August 21, 2010, 12:00:17 pmis it the same iron core used for the power transformer??