Preproduction model is finished, we are recalculating wire thickness to get the same DCR as in the original. Thanks to CJ on GroupDIY !
Static screening is a matter of course and there will be a PinOut PCB as well.
Mu metal sreening won´ t be necessary.
Prototype is optimized with 0,09mm wire in the second proto, this value gets close to the original DCR:
P1 + P2 = 996,2 Ω (original 1024 Ω)
(S1 + S2 + S3) : 3 = 11 Ω (original 11,2 Ω)
Pin Out PCB to be added !
Stock brass plates are depleted and reordered. PCBs arrived last week. Stock actually (2020/12/23) is 40 pieces.
MD 72/2, incl. Pin PCB: € 108,-plus shipping
The above picture could lead to the conclusion, one might be able to solder the trafo to drip´ s PCB directly. No, you can´ t. The pictures are taken to show the possibility to mount them, regarding the size.
This T 188 is built to original specs and for sale here. Bobbin with pins make it possible to mount direct to any PCB (not drip´ s !) or to connect to with Pinout PCB.
With the help of an experienced trafo winder ( thanks to Enzo !) and one of the rare german sources of EI 48 mumetal core material still being produced in Germany we were able to develop a replica of the venerable T188. Grading has changed over time, but this material is something in between "Dynamoblech IV", the old (pre WWII) core material for transformers and a modern equivalent. I doubt, the old "german gun - material" does in fact produce the desired "sound".
Anyhow, reason enough to give it a go.
We deconstructed an original HAUFE T 188, to see how it was wound - arrangement of coils, interlacing, thickness of wires etc.
Static screening as used in the original. With the start of the batch production we found proper copper strip, which works optimally in reducing capacitance. Gathering more information I used the contacts I had to people engaged with the company originally producing these parts in Usingen/Germany.
Our MD 188 has 2 primary windings with 290 DCR each, 1 secondary with a center tap and a total of 590 DCR.
DC resistance is very close to that of Haufe transformers (which came in a wide range), sound is very close, too.
Lp = ~ 3,4 H (10kHz), Cp = ~ 74 pF (10kHz), Rp = ~ 490k (10kHz)
EI 625 core material from US was tested as well. Sounds similar, but is not as smooth as the EI 48. Measured values deviate. Would ask for recalculation. Lp = ~ 1,5 H (10kHz), Cp = ~ 166 pF (10kHz), Rp = ~ 1,5 M (10kHz)
Our MD 188 MK.II is identical except the DCR, which is higher. P1: 336 Ohm, P2: 338 Ohm and S: 675 Ohm.
MD 188 MK.II, incl. Pin PCB: € 108,-
µ metal helmet € 39,-
Set U73b (3 MD 188 MK.II, incl. Pin PCB, 2 µ metal jackets and 1 MD72/2) € 452,-
Value destructed, for the sake of gaining experience ... actual result.
THD / noise values:
1. intermittent line 2o Hz
2. intermittent line 50 Hz
3. fat line 100 Hz
4. intermittent line 200 Hz
5. intermittent line 500 Hz
6. fat line 1kHz
7. intermittent line 2 kHz
8. intermittent line 5 kHz
9. fat line 10 kHz
10. intermittent line 20 kHz