MK7 - tube mic project

[Jonkan]

Thanks guys!

Any experience with russian k40y9 PIO caps? I might have found some in sweden a bit cheaper than the jensen pio caps.

Im intrigued what the difference could be, but im not sure how i can really test it as placebo is such a strong effect when comparing these things.

It will certainly feel cooler to have russian military caps in the mic, than regular polyprop, thats for sure!

/J

 

[Gus]

If you don't know you measure.

 

[ioaudio]

test on adjust is time consuming, but definately the best advice.
having a reference mic to guide you, your own voice reveals most of the details. check proximy in regards to cap-value variations.
record and document your findings, only change 1 parameter at a time, and find your prefered setup.
isnt this the wonderful thing about DIY - try all the choices, forget marketing bs, form your own opinion.
enjoy,

-max

 

[Jonkan]

I just realised i might have ordered the wrong 100k plate resistors. I have 0.6w metal film resistors, but on the pcb it says 1w. Im guessing this wont work, right?

Is it fine to use carbon film here, or is it better with metal film if i need to get myself some new resistors?

Thanks!
/J

 

[ioaudio]

no problem, metal film 0.6 works.

 

[Jonkan]

Cool!

One more quick one: Is it the 47nf cap that is supposed to go through the third glass tube?

/J

 

[ioaudio]

no, nothing feeds through the third glass tube.
it is used as a isolated stand off with the components mounted from above (68M + grid + 1nF + capsule front)
-max

 

[buschfsu]

is there a replacement for your bv7 offered by cinemag or others incase iwant to build this circuit and in the event that you run out of lams or stop making them?
thanks

 

[desol]

Here's the sockets i ended up ordering. Got them from: http://www.evatco.com.au/webcat1p12.htm

Part #S-B9A CWSF. They fit perfectly, bolt holes are ok, no mod's needed and they came with shields.
Cheers.

 

[ioaudio]

...in the event that you run out of lams or stop making them?

actually i invest in stamping and annealing my own laminations, and made some serious progress recently. however it will need some time before i can produce bigger quantities.
i still have some of the original lams which i intended to keep for my own mic developments, but now since i know how to make them myself, i just decided that i will offer another batch of original mk7 sets - in about a month. i have to order new pcbs and parts etc.
again, it will be announced here in the thread, and there will be no list.

thanks to all!
-max

 

[noulou]

...in the event that you run out of lams or stop making them?

actually i invest in stamping and annealing my own laminations, and made some serious progress recently. however it will need some time before i can produce bigger quantities.
-max

Very, very impressive. Can't wait for you to start chucking out transformers for all kinds of projects Austrian-Sowter style.

 

[Jonkan]

Cool! You are crazy dude

Another quick one. Max, when you used the thomann micbodies, did you find that you have to isolate the capsule mount from the rest of the mic body somehow, or is the rubber enough?

/J

 

[ioaudio]

i think i used additional isolation - but i dont have access to the mic right now so i cant say for sure if the mount needed it (i remember i made a isolation though).

 

[pH]

when you used the thomann micbodies, did you find that you have to isolate the capsule mount from the rest of the mic body somehow, or is the rubber enough?

I can answer this one, in fact I already did.

I posted in this thread that I had to wrap the metal couplings with teflon tape to additionally insulate it. Don't trust the stock mount.

 

[Jonkan]

Im thinking of using some ptfe shrinktube between the capsule mount adapter and fastening it all with a plastic screw...i hope that will work.

/J

 

[Davo]

Could someone explain how I would attach a dummy load to the heater.... I'm getting 14.3v unloaded
and don't want to connect it before testing.  I'm using an EF86

Thanks!!!!
dave

 

[Gus]

Ohms law.  Look up the current draw of the heater and pick a heater voltage you want.

Heater voltage / fil current = load resistor this will be off a bit if under or over heated but should be close enough for testing.  Then you need to calculate the power E X I or I^2 X R and pick a resistor of a higher power rating then calculated.

There is also the use of a CC load bank but the simple resistor load bank should work.

 

[smallbutfine]

Great to hear on your forthcomings on getting lams for a new batch of your bv7, Max.
Man, producing/stamping your own lams - that is really 'hardcore' DIY!
Very, very appreciated.
(I missed the first batch and thought it was a one-time opportunity.....)
I will definitely order at least one or two kits from you next time----

Thanks for this great project.

Kind regards,
Martin

 

[Davo]

Thanks Gus!! ;D

 

[bradb]

i'm screwing in these new sockets and worry that the little rise in the metal socket tab (you'll see) is going to not make contact with the tiny bit of exposed trace underneath... so i scraped some green away and will solder the metal socket tab to ground on the round pcb.  You'll see..

definitely NOT a showstopper on these sockets, you just gotta make sure to complete the ground connection.. we are bringing ground to the top of the round pcb thru the mounting screws, so everyone needs pay attention here.