U47EF Oliver Archut version

[Spencerleehorton]

Thought I’d document this as haven’t really used this U47 as when I built it many years ago I didn’t really use it as it ended up being noisy, a rogue hum.
Original The psu had a couple of normal transformers, both 15v, one at 12va and one at 8va. I’m assuming the 12va (0.8A) one had 2x6va windings and the 8va (0.5A) had 2x4va windings.
12va was one the heater and 8va was on B+.
The pcb for the psu was the same one as per vintagemicrophonepcbs.com U47EF as well as the microphone pcb.
The tube is a EF800 and uses 275mA.
From the build thread it says to use a 12R-30R load resistor.
The reed relay is only 5v and uses a 10k in R5 and 510R in R9 to get the 5v, relay uses( 10mA) and has 12k as load resistor.
B+ started with 220vac x 1.4 after diode bridge gives 308vdc.
B+ had R1 as 4.1k and R3 as 3.9k and R8 at 10k trimmer and I could wind down to 105v.
H+ started at 15vac x 1.4 which gave 21vdc after diode bridge had R2 as 5.2R, R6 as 13.R and R11 as 13.1R and had 25ohm 5W pot which could adjust easily to 5.05v.
All pins connected apart from pin 3 on mic socket.

Psu and mic sockets

Pin 1 to pin3 xlr
Pin 2 to pin2 xlr
Pin 3
Pin 4 to H+
Pin 5 to B+
Pin 6 to pattern (5v) for relay
Pin 7 to gnd

All seemed correct but getting hum?
So I have taken apart psu as case wasn’t ideal and started again.

My new psu is slightly different

B+ transformer is now 110vac (measures 125vac)
H+ transformer is 18vac (measures 22vac)

 

[Spencerleehorton]

bit confused about this reed relay voltage? mine is 5v so does that mean that i can anything above 5v to initiate it? as with the R5 10k and R9 510R thats what i had and it was working?

IM assuming the winding attached to the relay goes on the middle or COM connection, then switches between the 10k or the 510R which is down to GND? but this would be sending about 60v to the reed relay which is a 5v one?

 

[Khron]

Ohm's law, anyone? And what about a datasheet for the relay?

 

[Spencerleehorton]

5v reed relay datasheet here, its the EDR002

https://static.rapidonline.com/pdf/71149_v1.pdf
im getting a hum but cant track it down? even with PSU of when i connect mic and connect output XLR i get hum, when using other PSU when i connect all hum goes away when i connect XLR?

its doing my head in!!!

 

[Khron]

Coil resistance for that seems to be 500 ohms. Can't say anything else without a schematic, since part designators (R1, R3 etc) kinda don't mean anything.

 

[Spencerleehorton]

well ive found at least 3 bad points on the mic pcb which ive had to re wire, solder joints which have just failed for whatever reason.
where the valve socket attaches a a right angle the pads have failed and where acting as gnd points as well as holding the tube socket.
superglue has helped and ive run some wires on pins 5 and 6 to gnd, as well as pin 3 wasnt connected to pin 1 on the mic socket pcb?
also the heater trace was failing so ran another wire there!!
plugged it in and have ran the voltages again and gettting B+ 120v and H+ 5.05v, lots o bubbling and farting for a while, then just stopped.
hum is still there!!!!

 

[TLRT]

well ive found at least 3 bad points on the mic pcb which ive had to re wire, solder joints which have just failed for whatever reason.
where the valve socket attaches a a right angle the pads have failed and where acting as gnd points as well as holding the tube socket.
superglue has helped and ive run some wires on pins 5 and 6 to gnd, as well as pin 3 wasnt connected to pin 1 on the mic socket pcb?
also the heater trace was failing so ran another wire there!!
plugged it in and have ran the voltages again and gettting B+ 120v and H+ 5.05v, lots o bubbling and farting for a while, then just stopped.
hum is still there!!!!

View attachment 111262

View attachment 111263

Did you have the PCB's from Dany or from (ex-)micandmod? They copied the pcb with errors, I remember i sent a sample to Dany.

 

[Spencerleehorton]

this one was definetly from dany, it might have even been a prototype, the main problem i think is now the switch for the polar pattern/ relay supply and wiring the gnd correctly as at the moment im not using pin 3 on the mic socket but Pin 1 of the XLR in the PSU is connect to pin 3 on the mic socket.

 

[Spencerleehorton]

let me clarify, the hum im talking about is there even when the PSU is not turned on and the XLR is plugged into the PSU as well as the mic cable plugged into the mic, but the PSU is not on.
when i plug every other mic in like this, the hum goes away as soon as i plug the mic cable into the mic.
so this leads me to think the problem is within the mic.

 

[Spencerleehorton]

right, ive now changed the transformer inside the mic and this has fixed the initial hum i had, now thats out the way i can hear a little PSU hum, so i will tackle that!!

 

[Spencerleehorton]

I have put in a 5k trimmer with 33uf cathode bypass, disconnected R3 and R4 legs from pcb and connected them together, then ran the 5k trimmer from pin 3+1 to gnd, set at 2k, no hum!! glorious U47 goodness at long last!!

 

[MasterEvan07]

Man, circuit gremlins are the worst. Sometimes I thank the gods of DIY that after I build anything it even works right...I mean, I test continuity all along the build and voltage health when firing up and I always make sure everything is shiny solder joint-wise, but you just never know if something might be missed.

My most recent build, an Ela M-251, was my first tube mic build and my first tube mic PS build...when I fired it up the first time and it was beautiful with no hum or artifact issues it was wonderful.

Glad you tracked down your issue!

 

[Spencerleehorton]

Great choice ELAM251, i've built one as well and use it a lot.
Now that the U47 EF is working correctly without noise i've recorded in some acoustic guitars and vocals and im gobsmacked on how great they sound, i think i might build a turret version of this.
still need to figure out how to wire the 5v relay though!!!

 

[TLRT]

let me clarify, the hum im talking about is there even when the PSU is not turned on and the XLR is plugged into the PSU as well as the mic cable plugged into the mic, but the PSU is not on.
when i plug every other mic in like this, the hum goes away as soon as i plug the mic cable into the mic.
so this leads me to think the problem is within the mic.

There was a post we made,the grounding scheme can be incorrect. I made some of these mics and I have to put gnd selection switches(dpdt switch the "audio gnd" to starground or separate them. Gnd the audio xlr to starground first.

 

[Spencerleehorton]

Be good to see and understand fully that post if you have it?

Going to try and use the heater 5v for the relay

 

[Spencerleehorton]

I think I may have figured it!!
105v is my B+ with the 10k 1W that will give me the 5v at 10mA which is what the relay is rated at.
Then I need to add a resistor 510R to B+ to get the 10mA so the 105v doesn’t change.
Hopefully this is correct now and I’ll implement when I get some more time.

Just need to bring down B+ a bit more to 105v and I’m rosey!!

 

[TLRT]

Be good to see and understand fully that post if you have it?

Going to try and use the heater 5v for the relay

You have hum issues,right? We posted an updated grounding scheme in Dany's topic.

 

[Spencerleehorton]

I’m have eliminated the hum by putting in a cathode bypass but I would like to be able to have it as close to the original as possible without the cathode bypass.
If your able to share the link maybe?

 

[Spencerleehorton]

Omni on the guitar and cardioid on drums, couple of feet away from drums.

 

[TLRT]

I’m have eliminated the hum by putting in a cathode bypass but I would like to be able to have it as close to the original as possible without the cathode bypass.
If your able to share the link maybe?

Hi it is here:
https://groupdiy.com/attachments/1653742587509-png.94571/Discussed:
https://groupdiy.com/threads/d-ef47-tribute-to-oliver-archut-u47-build-thread.56878/page-34