U47 multi pattern build

[Spencerleehorton]

its definetly a step down transformer right? 6:1 should be the right ratio i thought!!
as in mic side pri should be 6 and to socket should be 1.

 

[rock soderstrom]

its definetly a step down transformer right? 6:1 should be the right ratio i thought!!
as in mic side pri should be 6 and to socket should be 1.

right. Original BV08 is 6.5 to 1. EF80(0) will work with 7:1 or more, too.

 

[Spencerleehorton]

well the helarious mistake this time was i'd put in a 47mH inductor in place of a 1G resistor! looked pretty much the same!!!
all works perfectly now!! doh!!

 

[rock soderstrom]

well the helarious mistake this time was i'd put in a 47mH inductor in place of a 1G resistor! looked pretty much the same!!!
all works perfectly now!! doh!!

Very good, you are always very creative with your mistakes!

I would solder another resistor into the position of the 20R so that you have some pre-filtering. How much voltage do you have at the input of the LM317 now?

 

[Spencerleehorton]

10v at input so as there is no noise i think im good?

 

[rock soderstrom]

10v at input so as there is no noise i think im good?

Basically yes, but a small resistor at this point would still form a nice RC filter with the following large capacitor. With a 1R resistor, approx. 0.3V would be converted into heat, the LM317 would still have sufficient voltage to regulate and would become less warm. Win - win.

0.3A x 0.3V = 0.09W ---> 0.6W or 1W type resistor would be sufficient

 

[Spencerleehorton]

i'll see if i have a low 1watt resistor and put it in, thanks again for all your help bud

 

[Accelerator]

Its definetly a step down transformer right? 6:1 should be the right ratio i thought!!
as in mic side pri should be 6 and to socket should be 1.

Yes, the BV.08 is definitely a microphone output step down transformer with 6.5:1 ratio.

The primary side of the 6,5 should be connected to the 1μF/250V coupling output capacitor - ground, the secondary side of 1 should be connected to the socket…

The BV.08 it is not the “perfect match” for the EF80(0) tube with 100KΩ plate load, but you came pretty close…

 

[Spencerleehorton]

I’ve got a couple of 7:1 transformers on order so will check them out

 

[Spencerleehorton]

I put in 3 x 5R in paralell to get 1.6R in replacement of the 20R, all sounds good, it was pretty quiet anyways but probably even quiter now.

well worth building this version if youve got some fibreboard and some turrets, modding the psu was much less of a pain than building one from scratch, having all the diffferent polarities really helps as well and buying the bodies saved me so much hastle and looks so much better than my versions.

 

[rock soderstrom]

I put in 3 x 5R in paralell to get 1.6R in replacement of the 20R, all sounds good, it was pretty quiet anyways but probably even quiter now.

Perfect! Do you hear a difference in noise when you change the heater voltage? (6.3V vs. 5V). I would be interested to know how you see this.

 

[Spencerleehorton]

Getting hum when I go from cardioid to omni with pattern selector, B+ voltage goes up to 142v from 120v? Then after 30 or so seconds after sound has cut out, B+ drops to 112v and can hear mic working but much lower output, if I click back to cardioid output goes up and if I goto to fig8 output goes up a bit more, fig8 back capsule doesn’t seem to actually be fig8?
When I click back to cardioid from fig8 it cuts out again but comes back after 30 seconds?
No hum on cardioid or fig8 positions , hum comes in from cardioid to omni?

Any ideas?

 

[Spencerleehorton]

The only chassis gnd is from iec, there is another gnd wire connected to the top lid.
The 3 pin xlr pin 1 is connected to chassis tab.
The 7 pin xlr pin 7 is connected to chassis tab but no wire connecting 3 pin chassis to 7 pin chassis.

 

[Spencerleehorton]

I’m going to revert to this pcb and see what gives.




I will make the relevant changes to get the desired voltages.

 

[rock soderstrom]

I’m going to revert to this pcb and see what gives.

View attachment 134715


I will make the relevant changes to get the desired voltages.

This is probably not the worst idea, first establish basic functionality (cardioid only, stabil voltages, no hum) and then take care of the polar pattern switching.

I've read your other posts, but I have no idea what's going on...

 

[Spencerleehorton]

Me neither that’s why I want to go to what I’ve done which works well.

 

[Spencerleehorton]

Should I replace these small wattage 130k resistors to 1/4 Watt 150k on the polarity switch?

 

[mjmajilton]

No. It’s just a voltage divider. The resistor values are mostly arbitrary.

 

[Spencerleehorton]

Ah ok, just wondered as between different psu’s there seemed to be some difference.
Hopefully get to the bottom of this noise and why it doesn’t play ball when mic connected!!
Thanks again

 

[Spencerleehorton]

well ive rebuilt the PSU and ended up getting pretty much the same problem!!!
so it must be the mic end, im going to change the 3 x 10nf caps in the mic and see if any improvement and double and treble check all Connections again!!