MK7 - tube mic project

[EEMO1]

no. no sound at all. I think I topped it with this one!

i'll take some measurements, though I did that already, looked good to me, but I guess I was wrong.


edit.

im looking at the schematics and pictures of the self bias. my print i have on my workbench does not have ground connection pin 4 to ground... DOH!

i don't remember if i have the transformer lams connected to ground via the tab. if not, i connect that? it's on the schematic too...

 

[ioaudio]

the schematic refers to the forced bias version - check the first post for the self bias wiring.
the connection of the transformer lams to ground is not crucial.

 

[kilmister]

Hi all!

Has anyone used EF804S tube in here?
I'm gonna make one of these babys and have allready few of these tubes.

-Paavo

 

[djn111]

Hi,

Should work fine, only check the heater current and adjust the bias resistor to match.

DJN

 

[mad.ax]

The EF804S is not a drop-in replacement for the EF86. Check the pinouts!

Axel

 

[djn111]

Hi,

Yes sorry you are right , but it will work when adapted

DJN

 

[mad.ax]

It will work sure! you're right too And it will probably work very well if a real TFK EF804s is used (not the false new Russian stuff branded as EF804S...)
Just thought it was worth pointing out that one need to rewire accordingly.

Axel

 

[EEMO1]

here's some pics of my build. I guess it´s time to plan building the real psu instead of the crappy t.bone mess...

bigger pics here:
http://twin-x.com/groupdiy/thumbnails.php?album=379

 

[Skylar]

Why did you pull out the 0.22F super caps?

 

[ioaudio]

i´m not 100% sure so i have to ask - did you solder the pins of the transformer? (thats why i was asking for the pin2-3 measurement of the output xlr)
the wiring on the round top pcb should be cleared - the anode wire should not touch the grid wire (pin 9)

 

[EEMO1]

hey,

skylar, the fixed bias doesn't need the extra ripple smoothing... i think?


ioaudio, touch as in the insulation shouldn't touch the grid wire? and yes, I soldered the pins.

 

[ioaudio]

the fixed bias doesn't need the extra ripple smoothing... i think?

thats right.

EDIT: i just re-read what i wrote: i got that mixed up, you will need the filter caps for the fixed bias but NOT for the self bias.

>>touch as in the insulation shouldn't touch the grid wire?

should not touch, yes.

 

[EEMO1]

you recon that the mic giving no sound could be because of this?

 

[ioaudio]

not really, no.

 

[EEMO1]

time to do the real psu and throw away the bloody t.bone crap.

 

[rodabod]

time to do the real psu and throw away the bloody t.bone crap.

I'd recommend making the usual measurements; each of the PSU pins unloaded, plate voltage, cathode voltage, heater voltage, polarisation voltage before Hi-Z section. And transformer continuity as Max suggested. Probably something very simple.

 

[kilmister]

The EF804S is not a drop-in replacement for the EF86. Check the pinouts!

Axel

Thanks for nice picture.
Yes I know it's more like blow-in substitute if replaced directly 8)

I'm hoping noise-floor goes down with EF804S referred to EF86.
Haven't play too much with tubes yet so it's all pure assuming.

-Paavo

 

[mad.ax]

EF804S offers a different pinout which means less crosstalk than the EF86, and genuine TFK used a special cathode material which is advertized as microphonic proof...
So, wrt these parameters, EF804S should be better than a regular EF86...
Now, in tube microphone apps, no matter what tube you use, the lowest noise floor is dictated by selection process... Out of a bunch of tubes, some will be less noisy in a high impedance circuit...
My point is: listen to all the EF86, PF86, EF804S, and other substitutes you can get your hands on, and use the one which perform the best...

Axel

 

[kilmister]

Thanks for info. It forwards for new questions.

How much rest of the circuit makes effect in tube selecting process?
I mean if I build two mics, one with EF86 and other with EF804S and select best tubes with them can I change good sounding tube from mic to another (and change pinout of course) and  achieve same results?

-Paavo

 

[mad.ax]

One could argue that there will always be some differences, but if your two mics are identical, and capsules reasonably matched, a good tube will perform well in both mics.
It sure will help to have two identical mics for comparison purpose.
Don't forget to give the tube enough time to warm up, and even burn in...

Axel