Custom "R-core" transformers on ebay - Page 1
Forum section: electronics / general

author: squibby
author_rank: Contributor
timestamp: March 27, 2024, 10:11:12 pm
content: As the thermionic valve freaks on here would be well aware, typical transformers are getting harder to come by with the usual 240 or 110 to 6.3V, 12V, 600V, 175 and many other different combos all wrapped with center taps, different current ratings etc etc.I bought a custom R-core transformer from ebay to solve this problem, and I can report, it met the specs I gave and it has performed flawlessly to date. They also appear to be quite nice quality. To be fair, they look and feel nicer than a 60 year old worn transformer, and I'm a believer that often, if it looks like it was put together with care, it probably will perform.I've bought two more now. I gave the specs on ebay, and the seller promptly got back with a price. search for R-core transformer.whoever is making these does a decent job and very efficiently priced. I just paid 80USD delivered to australia for a pair (yes two) transformers for a heathkit regulated high voltage power supply project I want to make.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 28, 2024, 12:23:30 am
content: Where are they shipped from?I would assume these are made in China to get such prices for custom stuff.

author: squibby
author_rank: Contributor
timestamp: March 28, 2024, 03:40:32 am
content: Absolutely. They are chinese.As electronics fans, we know what good stuff is good. We know Panasonic, Nichichon, Rubycon, etc etc and a thousand and one other brands that make good components already.What I like about forums like this, is that I can learn what unbranded chinese or otherwise manufactured stuff from amazon or ebay has been trialed out ultimately recommended. I've tried these transformers. They may or may not be very good, but....they seem fine to me for for the money. I will buy more if I can't find a second hand 50 or 60 year old transformer that I would expect to pay less for second hand.Attached photo of what I'm talking about

author: jonpaul
author_rank: Super Contributor
timestamp: March 28, 2024, 09:17:42 am
content: Well, easy to buy lams and DIY any mains trsf.Many off the shelf EI/EE trsf and lams readily avail.For valve (tube) audio aficionados a junked old CTR TV, scope, hifi will have a perfectly fine trsf for filament, B+.J

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: March 28, 2024, 11:05:54 am
content: Hi squibby,thank you for pointing it out.Is there any data given for breakdown-voltage / isolation?Or can you perform an isolation-test primary to secondary?In the old days Block had transformer-kits with the finished primary winding for 220Volts.Best regards

author: Zero999
author_rank: Super Contributor
timestamp: March 28, 2024, 11:31:16 am
content: Quote from: Roehrenonkel on March 28, 2024, 11:05:54 amGoing by the pictures, there are two bobbins. Assuming the primary and secondary are on separate bobbins, then it should have excellent separation, so it seems pointless conducting any insulation tests.

author: jonpaul
author_rank: Super Contributor
timestamp: March 28, 2024, 02:24:50 pm
content: capacitance high due to copper shading band wraop.Needs a Faraday shied if Cp=s is to be low.j

author: shabaz
author_rank: Frequent Contributor
timestamp: March 28, 2024, 04:53:11 pm
content: I purchased one of these recently, because I've got a DIY VNA that is supposed to have extremely high dynamic range if powered with a decent supply, and I wanted to build a linear PSU for it with as much filtering as I can reasonably manage. It arrived the other day, I still need to use it.From a quick initial examination, the outer metal band (copper?) is electrically connected to the stamped metal base. Both are lacquered I scraped at that to do that test.The yellow/green earth wire is not electrically connected to the outer band or the stamped metal base.The area where the wires disappear into the transformer looks a bit unusual; it is very hard to tell how they have done it because there seem to be some "elements" of construction (hopefully just for mechanical support, but I cannot tell) between the two bobbins. EDIT: There is anR core transformer discussionthat mentions that the primary may be across both bobbins, and the secondary could be across both bobbins.I will measure capacitance (I think by shorting all the ends of the primary winding, and shorting all the ends of the secondary winding) and then measure between that, and also measure each shorted winding to the yellow/green earth wire too, and to the metal base.EDIT: Now measured (all primary wires were shorted, and all secondary wires were shorted). Measured in the range of 200kHz down to 100 Hz:Pri-Sec: 97-99 pFPri-Yel/Grn: 99-100 pFSec-Yel/Grn: 290-300 pFPri-Band/Base: 83-90 pFSec-Band/Base: 84-88 pF

author: jonpaul
author_rank: Super Contributor
timestamp: March 28, 2024, 05:27:20 pm
content: Normal wiring, see spec sheets.Test cap:P1+P2 = RLC highAll S1+S2 = RLC low.Frame, shield, copper band = guardWould expect 100..1000 PF Cp=s with NO shieldperhaps 30..100 with guarded shield.https://canadatransformers.com/faraday-shield/j

author: shabaz
author_rank: Frequent Contributor
timestamp: March 28, 2024, 06:24:01 pm
content: I didn't understand what RLC high and RLC low meant* : (I've added the measurements above to that earlier comment.While I was at it, for a comparison, I took a normaltoroidal mains transformertoo (of slightly smaller at 15VA) and shorted the primary ends and shorted the secondary ends, and measured the capacitance to be 210-390 pF (in the range of 200 kHz down to 100 Hz).*EDIT: Now I realize you meant the high and low Kelvin clips of the LCR meter.

author: tooki
author_rank: Super Contributor
timestamp: March 28, 2024, 08:05:44 pm
content: For European customers who have a business they can order through: Multi Circuit Boards makes custom toroidal transformers at very reasonable prices:https://www.multi-circuit-boards.eu/en/pricing/toroidal-transformers.html

author: jonpaul
author_rank: Super Contributor
timestamp: March 28, 2024, 08:20:40 pm
content: RLC high = hot termina (RED) of RLC bridge or meterRLC low = rtn terminal (BLK) of RLC brige meter

author: squibby
author_rank: Contributor
timestamp: March 28, 2024, 10:14:03 pm
content: I’m putting these in power supplies for old 50’s/60’s stereos or a 1940’s condenser checker or an old high voltage regulated power supply…. These are pretty ‘rough’ applications where the difference between a high spec transformer and a basic transformer is unnoticable. I’m not suggesting one of these for your old tek scope.That’s why I like old electronics…. Very forgiving tolerances

author: coppercone2
author_rank: Super Contributor
timestamp: March 28, 2024, 11:16:48 pm
content: I would like to see a X core transformer. four windings, no purpose.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 29, 2024, 05:16:24 am
content: I would like a transformer built on a monohedron.

author: coppercone2
author_rank: Super Contributor
timestamp: March 29, 2024, 07:45:58 am
content: I wonder about klien torroids it seems more realistic to the klein bottle then any other flowable thing

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 29, 2024, 09:08:14 am
content: To be fair, the torus is a type of monohedron and that exists, but I was more thinking about a more elaborate kind of monohedron.I'm not sure the Klein bottle is strictly speaking a monohedron. Good question.