U47 multi pattern build

[Spencerleehorton]

Hi All,

While I’m waiting for the varnish to dry on my LO1166 transformers I thought I’d try and tackle the U47 multi pattern build.
I already have a EF80/800 microphone built, I just need to modify using Oliver’s schematic.


The psu I have is this one from thomann

https://www.thomann.de/gb/the_t.bone_psu_retro_tube_ii.htm

The mains transformer is 175v ac and 9v ac

B+
I will test the dc output but it looks like it will be in the 240v mark for b+ first node
So will need to drop 135v don’t know current yet? Thinking it maybe around the 1mA ?

Heater
9vac x 1.4 = 12.6vdc goes through 7806 regulator which can handle
Up to 1.5A current.
Not adjustable that I can see so will probably change for a LM317 so I can adjust with trimmer.

 

[rock soderstrom]

So will need to drop 135v don’t know current yet? Thinking it maybe around the 1mA ?

You can use 1mA to calculate your B+ rail, which will put you in the right ballpark. During the process, you can then make a fine adjustment with one of your series resistors if necessary. But 1mA is close enough for now.

Not adjustable that I can see so will probably change for a LM317 so I can adjust with trimmer.

LM317 is also a little cleaner and you can precisely set your desired heater voltage. Maybe it makes sense to install a series resistor to distribute the heat better? You can also use it to generate an additional RC filter in your heater circuit.

Edit: is there a schematic for the t.bone Retro Tube PSU?

Edit2: ist this the schematic? Similar?

 

[MagnetoSound]

Yes, it’s the same.

 

[Spencerleehorton]

well with 175vac and those voltages i end up with about 1.8mA when i work it out, will test my voltages and compare.
then try and figure out what im going to do.

 

[Spencerleehorton]

tiny bit confused about what capsule voltages i should be aiming for, as the U47 has B+ of 105v for cardiod and im not sure what voltages it is when in omni but im assuming it drops voltage?
on the psu schematic it says 0v for omni, 57.34v for cardiod and 116.6v for fig 8, should i now be aiming for these voltages with the changes in the circuit or still stick with the 105v b+?

 

[Accelerator]

tiny bit confused about what capsule voltages i should be aiming for, as the U47 has B+ of 105v for cardiod and im not sure what voltages it is when in omni but im assuming it drops voltage?
on the psu schematic it says 0v for omni, 57.34v for cardiod and 116.6v for fig 8, should i now be aiming for these voltages with the changes in the circuit or still stick with the 105v b+?

The uncorrected value of 105 volts was one of Oliver Archut mistakes back in time and produced several problems in their Blackspade UM17R microphone as you can read in this Blackspade UM17R microphone review by Sound on Sound…

Blackspade UM17R

Multi-pattern Valve Microphone

https://www.soundonsound.com/reviews/blackspade-um17r

Today Ami - Tab – Funkenwerk offers their Ami - Tab – Funkenwerk U47a Premium Kit $1290 with the corrected 120 Volts P.S.U., so a 120 volts P.S.U. is that you should look after for this Oliver Archut U47 Alternative Tube schematic with Remote Polarity Switch on Power Supply Unit…

 

[Spencerleehorton]

ive modded the PSU, changed R3 to a 50k trimmer but voltage still too high, will i have to remove the zeners? at the moment i can dial it down to about 148v with mic attached, 152-154v without mic
Heater adjusts fine, can easily get the 5.05v or 6.3v but there is loads of hum!!
the ushall story for me!! time to look through my notes and figure it out, as ive been here before!!

 

[Accelerator]

ive modded the PSU, changed R3 to a 50k trimmer but voltage still too high, will i have to remove the zeners? at the moment i can dial it down to about 148v with mic attached, 152-154v without mic
Heater adjusts fine, can easily get the 5.05v or 6.3v but there is loads of hum!!
the ushall story for me!! time to look through my notes and figure it out, as ive been here before!!

These infos may help you to your task as you P.S.U. is very “similar” to P.S.U that Apex “family” use…

the APEX 460 MODS

A.K.A. Nady TCM-1150, Carvin CM100, Alctron HST-11A

Power Supply Mod

by “mbrebes” and “Phil Townsend” on HomeRecording.com

http://homerecording.com/bbs/showthread.php?t=196274&page=6

Replaced the stock 1N4761 zener diodes with 1N4758 56V zener diodes.

This dropped the voltage down on the capsule from about 196V to about

112V.

Comment by “PhilGood:”

This makes a difference. I have 2 mics. I changed out the zener diodes in

one PS and tested them side by side. The harshness is improved. The mic

sounds much smoother and open. The detail is better and there is less

fuzz. Another added benefit is the tube seems to warm up slower, so it

means longer tube life.

By “Phil Townsend:”

Starting at the bridge diodes all the way back to the output. All that stuff is

part of the signal path. What I can’t understand is the use of zeners. A

choke / cap supply will sound MUCH better than the cap / resistor supply.

(Better= more dynamics, extension and less noise.) I haven’t run the "PSU

DESIGNER II" on it yet but I will in the next few days. That will tell a better

story. Single ended amps are Ruled by their power supplies.

Things to replace in the Power Supply

• Diodes.. replace with low noise schottky types

• Heater regulator replace with LT low dropout types

• all the caps (Black gates in the front and a high quality film cap (Mundorfs

or better) in the last position.

• Replace resistors with Mills resistors.

• Loose the PC board and go point to point with silver wire.

• Snubbers

• Mu metal shielding to keep the mike output well away from the PS.

• Lose the zeners.

Rebuilding the PS is not really a big deal but it would push the mike into the

ultra fi realm.

More specifics from “Phil Townsend” PS mod below:

C6 replace with 22ufd @ 350v Black Gate

C7 replace with 1 ufd @200v Western Electric paper in oil

C8, C9, C10 replace with 2200ufd@16v Black Gates

R15 replace with Mills 20 ohm at 5 watts

After C6 install Solen 3.3 ufd @ 400v***

***one side of the 3.3uF is grounded and the other side connects to the

circuit between the positive side of C6 and D11

Insulate all PC chassis mounting screws. One ground connection only.

Tightly twist both secondaries.

Let it run in for at least 48 hours. (with load)

Black Gates take a week of working to come up to snuff.

Don’t try to judge the sound until it’s broken in.

 

[Spencerleehorton]

That link doesn’t work btw.
I might try it without zeners and change a few bits, I suspect the hum is a faulty lm317 as I used the only one I had which was an old one!! Ordered some more, see where I get to today!!.

 

[rock soderstrom]

I might try it without zeners and change a few bits, I suspect the hum is a faulty lm317 as I used the only one I had which was an old one!! Ordered some more, see where I get to today!!.

Hey Spencer, I've got a Deja Vu!

Before you replace components, let's take a systematic approach. First confirm that the schematic I posted above really matches what you have in front of you. Please enter your changes and the voltages at the relevant points. It would also be interesting to see how much voltage the LM317 has at the input for regulation?

If you have hum again, remember what really helped last time. Take the ground for the mic from the output of the PSU and keep it away from the rectifier diodes and the first filter capacitors. (Hum = very often a grounding problem)

Remember, the PSU was built for a different mic, the voltages listed do not match your project.

Make your adjustments as usual, ignore the "ultra fi realm" nonsense and everything will be fine. As always!

 

[Spencerleehorton]

it was a simple wiring mistake!!, all works, phew!! lol, just need to lower voltage by 30v so nearly there, will change B+ resistors and should be done.
also the caps on the T-bone are 2 x 2200uf/16 and a 10000uf/16v everything else seems to be the same.

 

[rock soderstrom]

it was a simple wiring mistake!!, all works, phew!!

Deja Vu again! Have fun! thanks for schematic update.

 

[Spencerleehorton]

have put in a 47k in R1 and put a discharge resistor 160k to gnd at the end of B+
now can dial in 120v no problem.
6v on heater when i wind it up to 6.3v i get another hum that comes in? so again could be dodgy regulator or mains hum from somewhere?

the hum has changed now from earlier, sounds more like mains hum to me now and very low output from the mic?, the capsule in the mic isnt the greatest but does work and the transformer is a 5:1 and ive got it step down which i have in my others.

i have used some 100meg and 60 meg resistors in the mic in replacement of the 1G resistors, thoughts of this being a problem?

 

[rock soderstrom]

6v on heater when i wind it up to 6.3v i get another hum that comes in? so again could be dodgy regulator or mains hum from somewhere?

Perhaps the LM317 really has too little voltage to regulate? How high is the voltage at the input?

the hum has changed now from earlier, sounds more like mains hum to me now and very low output from the mic?,

mains hum could indicate that your faraday cage (=mic body) is not really tight and grounded.

i have used some 100meg and 60 meg resistors in the mic in replacement of the 1G resistors, thoughts of this being a problem?

smaller resistors make the mic noisy, but not dramatically noisy. I think your problem lies elsewhere, probably grounding.

 

[Spencerleehorton]

ok voltages wise on B+ im getting 265v at diode bridge and with H+ its 9.77v at bridge, ive kept in the 20R resistor before the LM317, probably be a good idea to remove the 20R right?

unloaded im getting 12.62v before 20R

 

[rock soderstrom]

ok voltages wise on B+ im getting 265v at diode bridge and with H+ its 9.77v at bridge, ive kept in the 20R resistor before the LM317, probably be a good idea to remove the 20R right?

Yes, lets calculate whats going on here. You got a EF800 (i guess) with 0.275A heater @6.3V. --> V=R x I =0.275A x 20R = 5.5V lost at 20R resistor

unloaded im getting 12.62v before 20R

12.62V - 5.5V = 7.12V @ the input of the LM317 --> this not enough voltage for clean regulation if you aim for 6.3V. You need more voltage for the regulator. Remove 20R resistor for a quick test.

Why the hell does everyone always give this unloaded voltages? I hate that, we want voltages under load in PSU talk...

 

[Spencerleehorton]

checked voltages on mic and only getting 28.75v on plate, only 11.2v between R9/R10 on oliver mic schematic, at R6/R7/R5 junction im getting 61v and after R5 im getting 5.93v.
will remove 20R and see if any better.
btw im using a EF80

 

[Spencerleehorton]

now getting 1.57v at kathode and 33.7v on plate, still a bit of a low hum and low output level

 

[rock soderstrom]

btw im using a EF80

which needs a little more heater current (300mA vs 275mA), otherwise almost identical

only 11.2v between R9/R10 on oliver mic schematic

your DMM plays tricks on you, because of the high impedance.

at R6/R7/R5 junction im getting 61v and after R5 im getting 5.93v.

good after R5 is high impedance land, again...

 

[rock soderstrom]

will remove 20R and see if any better.

this will fix your heater problem

now getting 1.57v at kathode and 33.7v on plate, still a bit of a low hum and low output level

without 20R resistor? voltages seem good...