D-EF47 Tribute To Oliver Archut U47 Build Thread.

[Bonnie1]

Hi Snork7,
Sounds like you're build definitely has issues.  Properly built with a decent psu the noise floor will be at least as quite as your average Fet.  Are you using pcbs or PP?  Are you using ef800, ef12, ef14?  What vdc do you measure on the filament, and B+?

 

[snork7]

Cheers Bonnie1 and thanks for responding!
Using poctop's pcbs, BV8R xfmr, EF800 tube, H+= 5.1V,  B+= 106.2V
Going around the tube connectors:
K= 1.097 V, 
Grid = -11.5 mV, 
5K = 1.097V,
H+=5.097V
HG= 1.4 mV
S= 0V
A=52.02V
G2=52.07
G3 = 0V

Also, it works on omni and cardioid.

Thanks!
Charlie

 

[Bonnie1]

Okay, at the voltage divider right after R7, (but before R8, R1) do you measure approx 60vdc?  Also, connector at bottom of mic take ohms measurement of the 2 audio pins used.

 

[snork7]

The downstream lead of R7 is 56.7 V (upstream is 106.2V).  Both audio wires at the connector pins are open (infinity).

 

[ln76d]

The downstream lead of R7 is 56.7 V (upstream is 106.2V).  Both audio wires at the connector pins are open (infinity).

So you found issue. Check and improve all transformer connections.
You should be able to measure resistance of windings from both sides of transformer.

 

[Bonnie1]

The downstream lead of R7 is 56.7 V (upstream is 106.2V).  Both audio wires at the connector pins are open (infinity).

Hi Snork7,  Not knowing when you purchased the BV8r can you confirm if the wire color corresponds with attached data sheet?

 

[snork7]

I bought them (2 of them) within the last year or so.  Yes they correspond.  Orange/white was 800 ohm while green/black was 32 ohm.  I resoldered them just in case.  Still no change.

 

[Bonnie1]

"still no change"
Are you not seeing 32ohms on the 2 audio pins?

 

[tonzauber]

looking at the diagram, there is one minor design flaw, from my point of view:

if you switch to cardioid, but for whatever reason the relay does not switch in, (Bad solder joint, loose contact, failure of relais), you will have 100V or more on the front diaphragm which will make it collapse.....

at the moment I don't see a simple solution for that, maybe somebody has an idea?

 

[ln76d]

looking at the diagram, there is one minor design flaw, from my point of view:

if you switch to cardioid, but for whatever reason the relay does not switch in, (Bad solder joint, loose contact, failure of relais), you will have 100V or more on the front diaphragm which will make it collapse.....

at the moment I don't see a simple solution for that, maybe somebody has an idea?

Why not power up lower voltage coil from Heater voltage?

 

[snork7]

Hey Bonnie1
I get 31.1 ohms on the audio pins at the connector at the bottom of the mic.  Yesterday I swapped the xmfr leads and that made it worse, so I swapped them back and the xfmr is definitely wired correctly.
Thanks so much for your patience!
Listening to Kings College Choir to get in the spirit!
Cheers to all,
Charlie

 

[snork7]

Hi In76d
Sorry, but I just realized the meaning of your post regarding the audio impedance.  Actually, I measured them individually to ground and that was incorrect.  I appreciate your help.
Thanks,
Charlie

 

[Bonnie1]

Hi Snork7,
Have you sorted the issues with your build yet?  To re-cap what we know so far.... it appears your voltages are correct, the transformer is wired correct. How about the capsule, have you verified it's a properly working capsule and connections to the capsule are correct and secure?

 

[hugo]

Hi all,
I will start this build...is there any errata to know, some update ?..What are the common mistakes ?
Thank you very much

 

[snork7]

Bonnie1
Thanks.  There is one more thing I will try and then I'll swap the capsule since I have two of them. 
Cheers,
Charlie

 

[Lordward]

Hi guys, a quick question:

I'm in the middle of this microphone build and I had ordered parts from all over the world.  After waiting 4 weeks for a set of 10x1uF 250V PIO capacitors they finally arrived.  However they were only 160V, not 250V. 

My question is - how dramatic of a difference would it make to use the 160V instead of the 250V? Could it be damaging or just pointless?
Eventually the right ones will arrive but I'm not in the mood to wait another month.

Cheers,
DW

 

[ln76d]

Your max voltage should be max around 110V if you build it properly so you shouldn't worry about 160V rated caps.

 

[Lordward]

Your max voltage should be max around 110V if you build it properly so you shouldn't worry about 160V rated caps.

Cheers, great!  Then I can at least put the thing together until the final ones arrive.
Thanks again!

 

[Lordward]

see attached pic. the T47 spec sheet shows the pins labelled A,B,C,and D. As does the PCB, but it is a bit confusing which pins are which on the transfomer itself. Pin A is the one closest to the 'T' in T47 on the pins side of the transformer.
Hope this helps!

Hi, I'm confused At Tab-Funkenwork the spec sheet shows as your picture (ABCD) and on my box it shows everything to be mirror imaged  :-\
Can anyone enlighten me??

(EDIT) I took away the pic because it wasn't showing up right.  Anyway, I got confirmation from TAB that it is as on my packaging picture which is odd because  it's the opposite of how it would fit in the PCB.  My PCB does not have pin holes for the T47 so I have to wire it anyway.  I hope this goes well  :-\

 

[hugo]

Hi, i received the mouser cart, but the 14k resistor of psu is 1/2w, instead of 1w writed on the pcb...is it still safe to use it , or should i order one 14k 1w ?
Regards,
Hugo