U47 with EF14 tube Build

[Spencerleehorton]

I’ve build the Dany Bouchard u47 power supply it has a nice big choke in it with loads of caps

 

[Spencerleehorton]

Is there a way to test the EF14 tube to see if the heaters gone?

 

[kingkorg]

Is there a way to test the EF14 tube to see if the heaters gone?

Just simple continuity test, there should be low resistance.

 

[terry setter]

And when switched to omni the level goes down a lot?

You should only lose about 4 dB when adding the rear diaphragm (switching to omni), but you will lose level for sure.

 

[Spencerleehorton]

Just tested the heater for continuity and there is nothing so this tube is gone!!

 

[ZHOUJUN]

In fact, you can try the double-tube 408A. I think the low-end is closer to VF14 than EF14, and the cost is lower. It can use independent 105V power supply. The components are designed according to the original circuit, and you can get good results without changing. Independent 105V power supply and heater There will be some differences in the tone of the separate power supply. After comparing it with the original U47, I think the tone of the independent power supply is closer to the original U47.

 

[Spencerleehorton]

yeah i could but i wont as this was a lesson in trying to be as close as i can to the original, ive order another EF14.

 

[Spencerleehorton]

as per the transformer i used a inductance meter to find the right way to connect it as the colour coding was completely different.

on the PRI it should be Black and grey connected giving 122.4H from Yellow to Green (598ohms)
on the SEC it should be White and Brown connected giving 2.87H from Blue to Red (16ohm)

 

[Spencerleehorton]

well that isnt right, as i get hum with the txf wired that way but no low end loss? will try another way??

you would think yellow to purple on PRI and blue to brown on Sec but this ends up in low henries when tested and no bottom end?

what is going on? no bottom end if i connect middle windings and get no henries on inductance meter
connecting the start to start i get full henries but loads of hum?

 

[Spencerleehorton]

Just tested a P2P version i built with a EF80 and the M7 copy capsule and BV08 which i rewound, Sounds pretty impressive and test voltages are all within where they need to be!!
Im doing a best mic shoot out today, so will share the results when done if anyones interested?
testing U47 EF80, U47 EF800, U67, U87i, ELAM 251, C12a, M49c, M49b and M49 Alt version

 

[rock soderstrom]

Im doing a best mic shoot out today, so will share the results when done if anyones interested?
testing U47 EF80, U47 EF800, U67, U87i, ELAM 251, C12a, M49c, M49b and M49 Alt version

very interesting!

 

[Spencerleehorton]

Well it seems my U47s are well out infront along with the ELAM 251 which sounds quite nice but not as mid forward as the U47s.
My U67 sounds terrible, so im goona have to look at that!! it has the most expensive capsule in there that i own and im completely shocked it sounds so bad!!
The U87 i have isnt much better either, quite a few of them suffer with overloading issues when playing loud on the acoustic guitar, will have to look into getting them all up to where the U47s are.
My pair of C12a sounds really good as well, very pleased with them.
The SE4400a im very disapointed in when comparing it to the U47s, sounds terrible on acoustic guitar and isnt much better on vocals, i actually thought this sounded pretty good at one point but now ive heard the U47s working well, its chalk and cheese!!!

 

[Spencerleehorton]

Lesson for today is cleaning capsules, what a difference its made to the U67 and the U87.
a nice clean and they are both up and running and sounding amazing again, keeping the capsules in a plastic bag from now on with a moisture absorber in there and make sure they get put away after each session rather than left out!!

 

[Spencerleehorton]

here is how ive done the tube socket

 

[Spencerleehorton]

just fired up this new version and works and sounds pretty good, little bit of ring from body, but could put some tape inside the body to probably stop this.

anode = 33v
H+ = 5.03
Kathode = 1.1v
B+ = 105.4v
2M/3M/100M node = 56.6v

 

[Spencerleehorton]

Is it worth trying to adjust the resistors to get 40v on the anode?
Was thinking I would put a trimmer for the 100k and wind it down and see if I could get close?

 

[Spencerleehorton]

I will see if I can do an LTspice sim and see if that helps point me in the right direction!

 

[MagnetoSound]

Is it worth trying to adjust the resistors to get 40v on the anode?
Was thinking I would put a trimmer for the 100k and wind it down and see if I could get close?

That’s up to you, but the readings are well within range.

 

[Spencerleehorton]

I think I’ll leave this one where it is then, sorry I thought it was better to get 40v on anode.
So I’m assuming anywhere from 30v to 40v on anode is good?
Kathode at 1.1v with heater in the 5.05v give or take +/- 10v?
And B+ at 105v +/- 5v?

Is that what you mean by in range?

 

[MagnetoSound]

Yeah. It looks close enough to work, and work well. Tubes vary. You can fiddle with different values for the cathode resistor and see if you can hear differences at different bias points, but personally, I feel this endeavour is best focussed on finding the best tone and lowest noise, than aiming for a specific plate voltage.

Lowering the plate resistor to get more voltage will sacrifice some gain, so that’s something to consider when adjusting values.

But YMMV. You know what they say about opinions. Let’s see what others have to say.