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| Small signal audio transformer design for a vacum tube microphone |
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| SK_Caterpilar_SK:
It's been a painfull 2 hours of trying wind 6 layers. I have ended up with 4.1-4.3H. it's not what I wanted but I'll take it... The 0.118mm wire ripped twice..I almost broke into tears. It's been 700 painfull turns (I think I was going layer by layer so it really depends on luck but if perfect it should be 125 turns a layer. Now it's time to do at least 30 layers...I don't have the proper equipment too wind it to count the turns. In the process I just went on AliExpress and bought one 600:15K transformer for 16 dollars. I may just not finish this at all. |
| SK_Caterpilar_SK:
Alright well..secondary turned out to be 4,2H and primary 64H.. The wire ripped at the last 200 turns or so and that was a rathe emotional moment after hours of carefully winding. It shouldnt really matter cause It would barely fit onto the bobbin..with previous winding failures atempted repairs to it with capton tape which only reduced more space from the bobbin.. I might have been able to wind more bravely with a coil winder and actually knowing the exact amounth of turns instead of finding out how many turns is one layer and average them out layer by layer...this way the wire was perfectly wound at least but I used a LOT OF IT. I dont think the HF performance of the transformer will be any good. Oh and because of it ripping now I have a 1:4 turns ratio which is 1:16 impedance wise...not what I wanted but it will do. I was supposed to include one more secondary that would be the feedback winding but guess what didnt fit and I dont have the counter so I simply just gave up on it. I may try the thing with this transformer and see if its any good but its likely I will eventually spend the hundred dollars on some other proper tranformer premade from somewhere in the world. Or go with the tube-semic output option.. But my labor I have done to get these results was not worth it, rather dissapointing. |
| H713:
Winding a microphone transformer is no trivial task... and one that probably requires more manual dexterity and patience than I have. You might look at what Edcor has to offer. While they aren't a Jensen, they also don't cost $100 each. Also, having measured quite a few, good audio transformers are pretty wide-band. I've measured Jensen transformers from about 20 to beyond 50 kHz. The distortion is really pretty tiny, less than .01%. The main reason transformers have fallen out of fashion for microphones and preamps is the cost. Really good microphone transformers are in the $100 range, so their use tends to be limited to the more expensive equipment. Putting a $100 transformer on each channel of a 40 channel mixing console will add a considerable amount to its price. It has been done, however, once again, it's limited to the more expensive equipment (Neve, Trident, API, MCI, Harrison...) Microphones are tricky, especially with tubes, so persistence is required. |
| SK_Caterpilar_SK:
--- Quote from: H713 on April 25, 2020, 08:20:23 am ---Winding a microphone transformer is no trivial task...Microphones are tricky, especially with tubes, so persistence is required. --- End quote --- Well all is true.. I do have the dexterity but not the luck with this try. Once I save up a little I will buy the winder and I will atempt this silly idea again. Surprisingly the one I have wound worked rather nicely. What I did is just built the circuit and applied signal to the grid of the tube manually. (Because I simply dont have a high value resistor for the microphone capsule and that would be at least 1G ohms). I could not mesure the frequency repsonse but by ear trough a buffer...its pretty dang close to what I would like. But I have not done any measurements yet. I will need to set it up for proper testing. But it worked however its not perfect because I couldn finish winding it because the wire snapped. Better luck next time with more proper gear so I can have a fighting chance. I might find some way to put the roll of wire onto ball bearings and just break it with felt and stuff... I will do what I can |
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