D-EF47 Tribute To Oliver Archut U47 Build Thread.

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Delta Sigma

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Use the current draws in Dany's schematics to get a rough idea of what resistors to use as dummy loads for testing. You don't need to be bang on, just ballpark to make sure you don't have a short or wildly high voltage under load.

If you want to test your pattern switch, you'd need a third dummy load equivalent to the relay coil. Personally, I wouldn't bother.
 

innercityman

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Use the current draws in Dany's schematics to get a rough idea of what resistors to use as dummy loads for testing

Can't find these schematics. I've read this post... dummy load for tube mic power supply?
So I know that 1/4W 150K to 210K should work for B+ and 20R to 30R 2W for H+
I have for sure a 1/4W 150K resistor, but don't have a 30R 2W so should I get one to my local dealer or do you think I can swap this H+ rough calibration with dummy load and just plug the mic in and then calibrate H+ ?
 
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Delta Sigma

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Can't find these schematics. I've read this post... dummy load for tube mic power supply?
So I know that 1/4W 150K to 210K should work for B+ and 20R to 30R 2W for H+
I have for sure a 1/4W 150K resistor, but don't have a 30R 2W so should I get one to my local dealer or do you think I can swap this H+ rough calibration with dummy load and just plug the mic in and then calibrate H+ ?
Do you have any high wattage resistors? 1W? 2W or different value?
 

innercityman

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Do you have any high wattage resistors? 1W? 2W or different value?

Yes I have but far from 20 or 30R... The lowest 2W resistor I have is 51K. I also have some vintage carbon 1W 150R resistors
 
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dasnevestheo

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Can't find these schematics. I've read this post... dummy load for tube mic power supply?
So I know that 1/4W 150K to 210K should work for B+ and 20R to 30R 2W for H+
I have for sure a 1/4W 150K resistor, but don't have a 30R 2W so should I get one to my local dealer or do you think I can swap this H+ rough calibration with dummy load and just plug the mic in and then calibrate H+ ?
I was in the same situation and ended up pluging the mic for the calibration, praying not to roast anything. I was lucky ;)
 

Delta Sigma

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Yes I have but far from 20 or 30R... The lowest 2W resistor I have is 51K. I also have some vintage carbon 1W 150R resistors
You could put four in parallel to get you close enough. Adjust your heater a little high then you'll be in the right ballpark to connect your mic.
 

wave

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Well, I inverted the bulb socket wiring and no more bulb or fuse blowing. I wired the heater transformer and measured H+ and I get a huge 27VDC... What did I miss or do wrong ???
+27V is not wrong. The mic needs to be connected to drop that voltage down. The tube requires about 300mA of current.
-Dave
 

innercityman

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Or if you have a bunch of small value 1/4W or 1/2W you could make a network to get close.

Thanks to Delta Sigma for reminding me the basics. LOL

So I put 5 150R 1W resistors in parallel to get 30R and made an H+ voltage check, and the minimum I can get with the pot fully clockwise is 6.7V, so I guess it should be ok. Unfortunately I don't have no more 150R resistors so I can't get a to a lower Ohm value for H+ dummy load. Now's the time to wire the mic and plug it in...
 
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innercityman

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Mic finished, PSU calibrated ! Audio test ok. I'll do some more serious tests later and comparisons with my MK-47. But I have one more question...

It seems to be hard to get the right tensions stable so do I have to warm the mic for a long time to precisely calibrate the PSU ?
 

Delta Sigma

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You should let it warm up for a while.

Remember a heater adjustment will change your B+. They also have a bit of a hysteresis. I find that after every small adjustment, you have to wait a minute as it may slowly rise/fall after the adjustment.
 

alphasnk

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Hey everyone!

I've built the microphone in point to point, it sounds great and it's super quiet, it was my first microphone build, so i was rather happy with the result!

I wanted to thank all of you who posted suggestions and their own experience, it was a great little 2 weeks learning adventure, thanks to you guys!

I wanted to half improvise things, so i made my psu with tubetown's TT VPUMP, powered with a 12vdc wallwart, from which i also get the h+ with a 317! I will gift this mic to my friend's daughter, so i didn't want her to have to carry a super heavy psu, especially if she's going to be moving around in her coming student life.. For those of you who want to try, it works very well, and it's not noisy at all! You only have to adjust your b+ in order to get 60 vdc for the backplate, and biasing the tube to adjust your plate voltage to where you like it!

I didn't care much about recreating the u47, i wanted to learn how to make a simple and good sounding tube microphone, and being able to 'tune' it to what i like in a microphone!

I used a k47 from a store on aliexpress from which i bought the microphone body, and it sounds pretty great i must say! It's not abrasive at all!

The transformer i'm currently using is a beyer tr dv 351 015, it sounds super great in this circuit!

I also bought a bv8 clone from that same store, but it seems i can't figure how to wire it (neither does the seller it seems), i get a huge volume loss and a hi passed sound, whereas the beyer gives something normal.. I'm attaching the 'datasheet'. I connected yellow / purple and brown and blue, measured 600 ohms from black + green and 16 ohms from white + red, i've tried it both ways, both sounded hipassed and useless! If you guys have suggestions please don't hesitate :)
 

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wstratton

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Here's a Soundcloud playlist that has me singing the same lines from a song using my D-EF47, once with a Mullard EF-80 tube and once with a Telefunken EF-802. So far I like the sound of the EF-802 best among the tubes I have tried in this microphone (I have an EF-184, but so far I haven't been able to get it to work without a lot of self-noise--maybe it needs to be burned in for longer).

https://soundcloud.com/wstratton%2Fsets%2Fd-ef47-tube-tests
Some other peculiarities about my microphone to take into account: the headbasket dimensions are smaller than standard, and the capsule sits further back from the front of the basket, rather than dead center. I am also using this microphone with a pre-built PSU from AMI, and I didn't do any calibration of the PSU. I have only gotten this mic to work in cardioid.
 

alphasnk

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Following as I have the same Chinese BV8 from AliExpress. Also how did you get the 6v filament voltage from the TtPump?
I didn't use the ttpump for the heaters, i used a 317 from the same 12v wallwart feeding the ttpump

I haven't retried the chinese bv8, i opted for these tiny beyer dynamic transformers from the 80s, which sound very good, and don't add much weight to an already heavy microphone!
 
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innercityman

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Here's a Soundcloud playlist that has me singing the same lines from a song using my D-EF47, once with a Mullard EF-80 tube and once with a Telefunken EF-802.

The Telefunken EF802 is my preferred too. More defined, smooth shinny highs. Did you adjust the heater voltage or was it the same for any type of tube ? I've read few pages before in this thread that for some kind of tubes, the heater voltage had to be encreased a bit. And what would have been even better, is to compare the Telefunken with other 802s from other brands. Just to see if Telefunken worth their price or not.
 

alphasnk

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The 802 was my fav at first as well, beautiful highs, overall clarity (i'm using a National 802)

Then i tried 806 S from Tesla, to me it sounded more like what people would call 'vintage', it's a nice thick sound, could be great on instruments

Then i tried pf86, from philips, mazda and telefunken, all sound great but the telefunken definitely has the edge for vocals, it gives the microphone that 'magical' thing. I was eager to try that to see if telefunken stuff was more a myth than a reality, but it sounds super great, it's true lol! I've got two telefunkens, both sound different, one has more lows which i found weird, but it's the one i picked for the singer i made the microphone for!

The philips and mazda sound like they'd be great for a preamp, more for uncolored amplifying, i think the telefunken tube gives the microphone a color that is what people would expect to hear from a 'tube microphone', at least for vocals, i don't know if you'd want that kind of sound on everything!

It's too bad we can't attach audio files :D!
 

wstratton

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The Telefunken EF802 is my preferred too. More defined, smooth shinny highs. Did you adjust the heater voltage or was it the same for any type of tube ? I've read few pages before in this thread that for some kind of tubes, the heater voltage had to be encreased a bit. And what would have been even better, is to compare the Telefunken with other 802s from other brands. Just to see if Telefunken worth their price or not.
Since I'm using a 'stock' AMI power supply, I haven't messed with the heater voltage at all--I tried building my own power supply based on the schematic, but I was in over my head once I got to the wiring stage.
The 802 was my fav at first as well, beautiful highs, overall clarity (i'm using a National 802)

Then i tried 806 S from Tesla, to me it sounded more like what people would call 'vintage', it's a nice thick sound, could be great on instruments

Then i tried pf86, from philips, mazda and telefunken, all sound great but the telefunken definitely has the edge for vocals, it gives the microphone that 'magical' thing. I was eager to try that to see if telefunken stuff was more a myth than a reality, but it sounds super great, it's true lol! I've got two telefunkens, both sound different, one has more lows which i found weird, but it's the one i picked for the singer i made the microphone for!

The philips and mazda sound like they'd be great for a preamp, more for uncolored amplifying, i think the telefunken tube gives the microphone a color that is what people would expect to hear from a 'tube microphone', at least for vocals, i don't know if you'd want that kind of sound on everything!

It's too bad we can't attach audio files :D!
Interesting! Hadn't heard of anyone using a PF86 in this circuit. I wonder if it's worth trying in my mic, considering I don't have the capability to adjust the PSU.
 

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