MK7 - tube mic project

[Jonkan]

Im guessing 200ma schottkys will do the trick for ef86 tubes if the pf86 doesnt solve my issues...let me know if im wrong. For the pf86...i dunno but i seem to remember around 300ma current draw if run as speced...so a little lower than that if underheated?

Bondo, whats that called in europe?

Im thinking of getting a friend help me make some new sleeves for the mics otherwise.

Main concern is sound though, looks are secondary.

Any ideas on how to get rid of the black text that says "pure condenser microphone" without harming the finish?

/J

 

[fazeka]

Bondo, whats that called in europe?

Auto body plastic filler

 

[ioaudio]

Any ideas on how to get rid of the black text that says "pure condenser microphone" without harming the finish?

with your finger nail - no kidding, try it, it works ^^

 

[matta]

Hey Guys,

Does anyone have a Thiersch ST7 capsule mount handy?

Mine arrived in the mail on Friday and I noticed that there is a glue/adhesive mounting the holder to the stand off.

I DON'T see this in the pic on the web and am wondering if anyoneelses is like this or the factory 'refurbed' this one.

Can anyone confirm if theirs also has this adhesive/epoxy? I want to know if I need to write to the factory etc.

Cheers

Matt

 

[Skylar]

Matt,

Mine is like that too.

You can see it in this picture:

 

[ioaudio]

ask thiersch. probably it´s not for mounting reasons but for isolation - just guessing here.

 

[Davo]

I'll parrot Skylar... my ST7 has the adhesive on it as well

cheers,
dave

 

[matta]

Matt,

Mine is like that too.

You can see it in this picture:

Thanks Skylar,

That is good to know, it is clearly something they do to all of them based on the 3 of us who own one.

I'd be interested to track who got which number! It seems yours is Serial 40, I'm 46, should we see whose went where? LOL.

Cheers

Matt

 

[Davo]

Mines got an 071 stamped on it... seems like I've got the latest model ;D

dave

 

[Skylar]

Mines got an 071 stamped on it... seems like I've got the latest model ;D

dave

Yeah, but those late-model mounts just don't have the same warm, vintage sound as the early ones like Matt & I have.
;D

 

[Davo]

:'( Lol  Damn you're right... gotta see where I can get one of the earlier ones, just hope they haven't gone
up too much in value  ;D ;D

 

[ioaudio]

;D


RE: new mk7 kits: i changed my supplier for pcb´s which was a bad idea, as they still did not arrive. it will take another while for the new sets.

-max

 

[smallbutfine]

Take your time Max, nothing to worry about. For example, I've been waiting 2 years for Dale's M7 capsules, so at least for me, time is not critical as long as I can get what I wanted.
I guess lots of people here do think like me.

Kind regards,
Martin

 

[Jonkan]

So i got my pf86 tubes yesterday and changed the *3.9r resistor to 4.7ohms, adjusted the heater to the correct value and fired up the mic.

A bit better, but still some hum.

I then tried adding some more capacitance on the heater supply. I had two 4700uf/25v caps lying around, so i parallelled them and added to the output of the heater supply.

Still humming, maybe a bit better but could be placebo since i cant compare directly.

The difference between input output on the lm317 is 12.8-8.2v= 4,6v right now, so that seems perfectly fine.

Any ideas what else i could try to get rid of the hum?

Or is it time to change the bias method ?

/J

 

[guavatone]

Today i finished two of my four mics (i finally got the capsule holders ive been waiting on), and also two psu units. Ive tried both mics with both psu units, and the mics pass sound.

One of them is very noisy, but I attribute that to the tube i have in it (i just threw in two leftover ef86 tubes that i had lying around at home).
/Jonas

Did you try swapping the good mic's tube with the humming mic?

-check for cold solder joints or just re-solder all points.
-Clean the flux at high impedance junctions especially

Can you describe the hum?

 

[Jonkan]

I recently changed the tubes from ef86 to pf86.

Both mics hum the same with pf86. I think its the normal power 50hz hum, and it goes away when i turn of the psu, and until the caps are drained the mics sound just fine.

Should i try adding like 20000uf more to the heater, or perhaps more capacitance to the B+ supply?

Ive cleaned everything with isopropanol and foam q-tips. Since both mics does the same, and with both psu:s, im thinking it might not be a cold solder joint or something like that.

/J

 

[guavatone]

Jonkan, do you get hum from the other  mics with the same PSU.

quadruple check grounds?

 

[Jonkan]

Yup, both mics hum with the psu. In fact all mics hum with all psu:s.

I think the grounds are ok, atleast they measure fine on my multimeter.

Ill doublecheck anyway if there is anything funky about the grounding. I didnt change anything at all with the grounding scheme from the stock sct700 mic.

/J

 

[seavote]

im using an ef86 in my build but would like to try a pf86 in a second G7 project(gyraf likes them and it seems ioaudio does too) im not having much sucess finding them in the states(or N. America for that matter). could someone point me to the place they got there's.
thanks

 

[ioaudio]

jonkan,

try changing the bias method. if the hum is gone after the change, you know that the heater supply has too much ripple, not the HT.

-max