------------------------------ From: brad.sanders@circellar.com Date: Sat, 15 Jan 94 03:35:59 -0500 [EST] Subject: Winding your own transformers To answer ymch%camars.kaist.ac.kr@daiduk.kaist.ac.kr (Young-Min Chung): >I am planning to develop a project to build a tube SE power amps using >triodes and gathering information. A few domestic sources of tubes and >other passive parts exist but output transformers are very rare and >expensive. I have a possibly outlandish suggestion to you. It works for me, and it works well. (What's with all these questions lately about building toobers?) What I do is accumulate 3 or 4 OLD RCA television power Xfmrs, cut the windings with a bandsaw (be careful of the laminations!) and rip out the old wire. The potting is old and will crumble away, and then you have some VERY good iron for winding output transformers. Mix up the laminations real well, to even out the differences in steel from one to the next. If none are available there, I have another good source - old US military equip. Any US made equipment from before 1965 really. I use RCA TV's because they seem to sound the best (?) and are available. British steel from this era would also likely sound good. All bigotry aside, stay away from Japanese steel, it saturates faster - possibly due to a lower nickel content? Now you can purchase some .060 teflon sheet, and whatever size wire you need (silver, insulated with teflon - best - or polyester) and wind your own ULTRA high quality output transformer. Make a form from the teflon sheet, and use a layer of teflon tape between each layer of windings. Teflon insulates only about 100v/mil, so take time between each winding to apply a layer of Sylgard 184 (this potting compound has a dielectric of about 600v/mil). As it is a silicone, put it BELOW the layer of teflon tape, and allow it to cure before going to the next layer (for 2-3 hours). For good info on designing your own transformer, the Radiotron Designers Handbook (RCA - 4th ed) has an excellent chapter, as does "The Williamson Amplifier" reprints. Teflon tape can be purchased at a plumbing supply store (no joke). Sylgard is made by Dow Corning corp, in Midland, Mich, USA 48686-0994. You can also use this for power transformers to help decouple mechanical hum. Once wound, pot it in a quality extruded aluminum box (using Sylgard 184), and you will have a transformer that will sound the same in 30 years as it did when first wound. Use teflon capacitors (available up to 20uF) and you will have an amp your great-great-grandchildren will be able to enjoy. Just remember electrolytics will have to be replaced in 15 or 20 years - so don't use them! Happy winding! nuke brad.sanders@circellar.com ___ Blue Wave/QWK v2.11 ------------------------------ Date: Mon, 17 Jan 1994 10:52:00 +0000 From: "henry (h.) pasternack" Subject: Re: Winding your own transformers. Brad Sanders writes: Thanks for the interesting comments on winding transformers. I'm under the impression that there is a fair amount of finesse involved in the design and winding of "ultra-high quality" output transformers. The texts I've seen emphasize the need for very thin layers of insulation, extremely regular windings, and fancy segmentation in order to minimize leakage inductance and winding capacitance. I'm curious whether you have measured the reactance parameters of your transformers. I also wonder if you know where one can buy new laminations of known high quality. -Henry P.S. In theory, my official new email address is 'hap@bnr.ca'. In case of trouble, 'henry@ego.psych.mcgill.ca' will also work. ------------------------------ From: Josef_Schwarz@do2.maus.ruhr.de (Josef Schwarz) Subject: Roll your own German style Date: Sat, 12 Feb 94 01:42:00 +0200 In a 1966 edition of the German "Funkschau" electronics magazine, I found the following instructions for making your own high-quality output transformer for a push-pull pair of tubes with ultralinear connection if required. I've translated these to the best of my abilities in technical English. Maybe someone can figure out iron and wire measures in American measures, that's beyond me. Originally by E.A.Schulze, Funkschau 1966, No.1, p.27f. Here we go: Example for 2*EL84 = 6BQ5 First the sectional area of the iron: Fe (in sq cm) = 200N : fu (N in watts, fu = lower limiting frequency, for 20Hz) =10 sq cm, (German norm core MD 102a) Primary windings calculated from voltage at max. power: U= sq root out of N*R (in V, W(atts), Ohms) for 2*EL84: U= sq rt out of 10(W)*8000(Ohms) = 280V number of windings: 115*U:Fe (sq cm) = 115*280:10 = 3240. For frequencies different from 20 Hz the factor 115 has to be altered: it's double for 10Hz, half for 40Hz. The transformer calculated in this way will have a hf limitation of 60(!)khz, the amp should limit at 30khz. The windings have to be interwoven; symmetry is vital. The winding chamber has got a flange in the middle. One chamber is to be wound clockwise, the other anti-clockwise. Between each primary winding for tube 1 and 2 place one secondary winding. The primary windings are divided into ten sections, the secondaries into 8. Now you calculate the secondary windings: these are 81 for a 5 Ohms speaker: U= sq rt out of 10(W) * 5 (Ohms) = 7.07V 115* 7.07:10 = 81 Thickness of wire should be calculated to fill about 80% of the chamber height, including insulation. The windings should also fill one layer at a time, and primary and secondary windings should have about the same winding height. Thicker wire leads to reduced loss. In the above example wire of .25mm for the primary windings, and .65 for the secondaries is recommended. The sectional view is like this: (p-primary,s=secondary) chamber I chamber 2 18 _ _ 36 17 _ p 324 wndgns p 324 wndgns _ 35 16 _ _ 34 15 _ s 80 wndgns s 80 wndgns _ 33 14 _ _ 32 13 _ p 324 wndgns p 324 wndgns _ 31 12 _ _ 30 11 _ s 80 wndgns s 80 wndgns _ 29 10 _ _ 28 9 _ p 324 wndgns p 324 wndgns _ 27 8 _ _ 26 7 _ s 80 wndgns s 80 wndgns _ 25 6 _ _ 24 5 _ p 324 wndgns p 324 wndgns _ 23 4 _ _ 22 3 _ s 80 wndgns s 80 wndgns _ 21 2 _ _ 20 1 _ p 324 wndgns p 324 wndgns _ 19 Primary and secondary windings are isolated by layers of laquered paper or teflon insulating tape (available for sanitary purposes). Start the primary windings at the centre flange, the secondaries at the farside flanges. Uneven numbers (1,3,33,35) are beginnings, even numbers (2,4,34,36) are ends. Secondary windings to connect: - 3+7+11+15+22+26+30+34 and - 4+8+12+16+21+25+29+33 - then: 16+33 and 15+34 Tube 1 is connected: - plate to 18, g2 to 2; tube 2 - plate to 36, g2 to 20. - B+ to 1+19. Hope this is helpful, if you want to 'roll your own'. Mr Schulze claimed the transformer would "meet extreme demands for quality", as it could be used with a high amount frequency independent negative feedback, bringing down distortion to fractions of one percent. Cheerio, Joe.