November 2016

I have bought some LL1673/10H from you, but the measured inductance (with my inductance meter) is only 6H. What is wrong?

2016-11-01T16:13:31+01:00November 1st, 2016||

Our power supply chokes are designed to work at 100/120Hz and with voltages around 100V. Most induction meters work at a few volts or less, at around 1kHz. This is not the correct operating point for a power supply choke, and the reading on the induction meter is usually around half the specified value of [...]

November 2015

Is there a CAD library for Lundahl Transformers products?

2022-11-16T10:52:21+01:00November 19th, 2015||

EAGLE CAD Lundahl library (created by Bob Starr of RTZ Audio): CADSoft EAGLE PCB Design Software is a CAD software available for a number of different platforms. A limited function version is available free of charge for personal use. Please see for downloads.

October 2015

June 2015

May 2015

Problems with LL1660 freq. response.

2015-05-28T14:09:51+01:00May 28th, 2015||

I’ve built an amp with 2A3 and LL1660. I like the sound of it, but was a little frustrated when I measured the frequency response today. Around 9.5KHz I get a climbing response that doesn’t go away until I’ve reached the end of the bandwidth of the amp. With a few measurements, I located the [...]

I was measuring the Inductance of the primary coil of the LL1649. It measures around 2-3 H with the primary coil in series. In general what is the optimum required H value for the primary. Why do you want to measure the inductance of a mains transformer?

2022-11-16T10:52:22+01:00May 28th, 2015||

The interesting parameter for a mains transformer is the no-load current. For our mains transformers LL1648 — 51 the no load current is less than 100mA, indicating a no load impedance above 2kohms at 50 Hz. (corresponding to 6H) The no-load current should be compared to the full-load current, which for a 250VA transformer is [...]

One of the LL1674 seems to be off-spec, the secondary static resistance should be about 605 ohm and 3 ot the transformers do indeed measure 600-608 ohm. The fourth one measures 560 and 600 ohm for the two seconday resistances, this would lead to an off-balance surely?

2015-05-28T14:06:03+01:00May 28th, 2015||

Gain matching and CMR would not be so good. Difference in copper resistance is due to difference in wire gauge. It is possible that we used wire from different runs or from different vendors. However, the number of turns should be correct. (I say ”should be” as shit do happens, even at Lundahls. But if [...]


Lundahl Transformers

Tibeliusgatan 7, 761 50 Norrtälje

Phone: +46 176 139 30

Fax: +46 176 139 35

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