Wow, did I mess that part number up. The choke is Lundahl 2733. Good catch Vitalstates. I have gotten to know Kevin very well. He holds "Audio Sunday School" which I attend regularly. My current preamp/linestage is his Mir K&K Audio | Mir Line Stage Preamplifier which I thoroughly enjoy. Before building the MoFo, Kevin measured the output at the 15 dB high gain setting. At 1KHz, at 1%THD, the Mir can swing about 42V p-p.
And thanks to all for the encouraging comments on my build.
And thanks to all for the encouraging comments on my build.
Last edited:
You should not forget Jack Elliano and Dave Slagle. Tube folks found their old school 3.5A chokes for 211/805/845 filament DC supplies to be of higher quality compared to off the shelf items. They may still offer exotic material selection such as nickel core, OCC, Litz or silver wire.... I'd like to measure/try a pair.
Hi Steve,
I notice your mod :
I notice your mod :
Are you sure C2 polarity does not need to be reversed? Your circuit shows positive lead connected to negative voltage, usually incorrect polarity destroy electrolytics rather quickly.
I've some MoFo prototype boards left .There is one isue , made a mistake with the outputcaps pitch it's 5mm instead of 10mm .In my boards I drilled two extra holes with a the right pitch see pic of boards and working module.Pitch input cap is 22,5mm
Send me PM if you need boards or info
Send me PM if you need boards or info
Attachments
Kp93300, the inductance value isn't critical but as was said earlier the type inductor in your picture is totaly unsuited. These type are usualy for filtering high frequency noise. What you will need is something like was specified in the article which means a big chunk of iron and copper of at least a kilogram or more. In other words a choke specified for 50 or 60 hz operation 40 mh or larger and rated for about 3A.
Only if it is VERY big. 50V 3A winding on 150VA un-gapped core.
This works like the microwave oven transformer that others have used. An un-gapped core with *heavy* DC in it will have low inductance (saturation). The best design would be to build the core not inter-laced (the way the iron stampings are normally assembled for AC work) but instead as two pieces (typically "E" and "I" shape) with one sheet of paper between them. However if you just use OVER-size iron, that works also. The interlacing on E-I cores is never a perfect magnetic joint, and the slight gap works if the core is very large for the job.
In Malaysia you may have local transformer repair shops. You can find the core-size of the Hammond choke on their web site. If someone here can count or estimate the turns and size of wire used, you can probably build a duplicate.
The turn count can be estimated by working one turn of fine wire around the choke core. Feed the choke main winding with about 6V of 50/60Hz from a large heater transformer. (A 1 Ohm series resistor is wise.) Verify the actual value of AC on the main winding. Then read the very small AC voltage on the added winding. If too small to read, try to get 10 turns. We can work out the main winding turns from that data. The winding size can just be whatever wire we can make that many turns fit in the core window.
Last edited: