Multi pattern U47 schematic

[Spencerleehorton]

Hi guys,

Been search for a multi pattern U47 schematic and came up short?

Is there such a thing?

Interested in doing this to the ef80 / ef800 Oliver version.

 

[shabtek]

more than 2 patterns?
borrow from other 3 pattern designs, Jakobs G7 comes to mind

 

[Accelerator]

Yes, Oliver Archut (R.I.P.) of Tab – Funkenwerk had made an U47 Alternative Tube schematic with Remote Polarity Switch on Power Supply Unit…

 

[Spencerleehorton]

Thomman do what looks like a nice psu which I think maybe be perfect for this, and for b stock £65 including p&p sounds good!

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

 

[Spencerleehorton]

Plugged in this mic today, it’s a U47 with EF800 with the t bone modded psu and I’m getting hum!!!
I think it’s always been there so need to find why and where???

 

[Accelerator]

@Spencerleehorton​

Plugged in this mic today, it’s a U47 with EF800 with the t bone modded psu and I’m getting hum!!!
I think it’s always been there so need to find why and where???

Does the t.bone PSU Retro Tube II gives you the 6,3 DC Volts / 295 mA that the EF800 Pentode Valve needs for the LT heater operation?...

Do you have install any zener diodes to tame down the HT voltage?...

If you had done the voltage taming with zener diodes, do you have install some other filtering capacitors to tame down the zener diodes pulse?...

Have you check out the P.S.U., the cable, the microphone, in short tern everything about “cold” soldering joins or any misjoings and mistakes?...

Have you got an extra spare EF800 Pentode Valve to check out if your EF800 Pentode Valve that you have now in your hand and use is microphonic?...

 

[Spencerleehorton]

I have several other u47s with ef80 in which have no hum, I have changed tube into them and tube is fine.
I will look at psu tomorrow and check all other bits what you’ve said.

 

[Spencerleehorton]

ok, well ive managed to get rid of the hum but now ive descovered the pattern switch cuts the mic out when i go towards omni?
seems fine the other way toward fig8 but when im at fig8 its only cardioid?

 

[Spencerleehorton]

only difference i have found on the polarity section is the C7 cap isnt 1uf its 220nf, the 150k resistor measures as 1.5M so will need to lift that to make sure its 150k.
one of the zeners by the way if lifted on the psu taking them out.

 

[Spencerleehorton]

Voltages look good on b+ and h+ will look at pattern switch and see what’s going on?

 

[Spencerleehorton]

corrected a wiring mistake on capsule but still wont correctly change patterns?
and hum seems to be back?

 

[Spencerleehorton]

I've got a few spare LM317 so i could change it, as this has been a source of intermitten noise before but the heaters seem to work fine?

as per the pattern switch im pretty sure i have it wired correctly now, apart from that cap which isnt 1uf its 220nf on the pattern selector it does seem to agree with the schematic?

 

[Spencerleehorton]

so far with testing this is what happens,
set B+ to 120v set H+ to 6.3v
set polarity switch to centre (cardioid) and get 120v B+ and 62v on polarity switch
if i then goto omni i get 0v on polarity switch and B+ goes up to 140-150v
if i goto fig8 i get 112v on polarty switch and 112v B+

any ideas, im sure its a wiring mistake but i'll check again!!

btw it was a 1.5M resistor where a 150k sould be, so ive changed both the resistor to 150k and the cap to 1uf but i only had a 250v one but should be fine as most is 160v

 

[Spencerleehorton]

after about 30 seconds maybe a little more in omni the B+ voltage does come down from about 142v back to 120v and omni does seem to work although there is a nice hum there?
back to cardioid and the hum goes away?
put in fig8 and it doesnt sound like a particularly good fig8 but when turning back to middle to cardioid the B+ voltage shoots up again and then about 30 seconds comes back?

so it seems its sort of working but not how i thought it would?
and the hum in omni isnt useable? and fig8 is pretty much cardioid?

 

[Papa Tango Charly]

The black Tbone SCT 2000 PSU is better quality. best
https://groupdiy.com/threads/is-it-...-microphone-circuit.84555/page-2#post-1098551

 

[Spencerleehorton]

The black Tbone SCT 2000 PSU is better quality. best
https://groupdiy.com/threads/is-it-...-microphone-circuit.84555/page-2#post-1098551

i've modded the PSU so i dont know what your putting that for?
is there a fix to my problem?
or are you just saying buy the other PSU?

 

[Spencerleehorton]

ive added 10000uf on the 6.3v side but can still hear a hum when the omni signal appears?
omni is also very low , drops by at least a half of the volume?

 

[Papa Tango Charly]

Oups sorry i didn't understand. best