MK7 - tube mic project

[JW]

Okay, I'm in for two sets!

 

[Arno]

I'm interested in two !

thanks,

arno

 

[tommypiper]

Is there a chance to modify this for other tubes? The EF804(s) is quiet, has been used in the V-series preamps and the REDDs, it's an EF86 variant, yet I've never seen it tried in a mic.

 

[ioaudio]

it is possible.
one of the reasons for using a chassis mount tube socket and hardwiring it is (besides having high insulation) that you can use different tubes/different pinouts without scratching the pcb.
for tubes with a 6,3v heater (ef86 etc) , the psu has to be modded to supply ~9vcd and two resistors (2,2R* & 3,9R*) have to be changed.

 

[bobschwenkler]

I'd be in for two. Is there Black Market thread for buying? What is the availability looking like?

 

[ioaudio]

i will make two runs at 25pcs/run. there will be no list, but i will post here when i open the sale thread at the black market so everybody who posted here will be notified. first 25 who paypal will get them.
~2 weeks from now on.

 

[pH]

I'd be interested in one as well.

Cheers
-Paul

 

[bobschwenkler]

Do you have an estimate on the price?

 

[ioaudio]

a ballbark figure, yes - read the thread.

 

[seavote]

bernbrue .. i know your inquirey about m ohm resistors was back on pg.1 of the thread but i just saw this
http://www.groupdiy.com/index.php?topic=30209&highlight=

quality???? worth a look i thought

 

[bobschwenkler]

[quote author="ioaudio"]a ballbark figure, yes - read the thread.[/quote]

I don't see a price figure anywhere. Just a brief mention of another project or mic that I'm not familiar with that you said the cost should be similar to.

 

[seavote]

the way i understood it. ioaudios pcb and bv8 type transformer for the project will cost about the same price as the t bone sct700 mic(the same mic he used for the body for the project). the sct700 cost 139 euros. about $178 U.S.

 

[bobschwenkler]

Cool, thanks.

 

[ioaudio]

re-reading what i posted i sounded harsh - sry bob, that was not intended.

 

[bernbrue]

[quote author="seavote"]bernbrue .. i know your inquirey about m ohm resistors was back on pg.1 of the thread but i just saw this
http://www.groupdiy.com/index.php?topic=30209&highlight=

quality???? worth a look i thought[/quote]

Saw this as well, thanks a lot seavote.
regards
Bernd

 

[bobschwenkler]

[quote author="ioaudio"]re-reading what i posted i sounded harsh - sry bob, that was not intended.[/quote]

Thanks, I appreciate it.

 

[ioaudio]

i updated some little things.

regarding the highZ resistors: i used RS-components nr. 247-7806 and 247-7834

 

[rodabod]

Max, regarding the plate to transformer coupling cap, did you select this by ear, maths, or by measurement?

I'm just interested in people's approaches to these things. Looks very promising by the way.

Cheers,

Roddy

 

[plumsolly]

would an apex 460 be a good mic to hijack for this project? the b+ is 195v I think - but that could be dropped no?
-Ben

 

[ioaudio]

[quote author="rodabod"]Max, regarding the plate to transformer coupling cap, did you select this by ear, maths, or by measurement?[/quote]

everything - i use math for ballbark figures,  build a vf14/bv8 reference amp to record samples and compare them in the computer.

things to consider mathematically -

Z(out) - C corner freq
Z(out) - L  corner freq
C-L resonance freq

0,33µF is the calculated value.

sonically i like 0,33 - 0,47 - 0,68 µF depending on the proximity effect of the capsule. it´s a good place for fine tuning this circuit.


[quote author="plumsolly"]would an apex 460 be a good mic to hijack for this project?[/quote]

the housing might be too slim. minimum inner diameter for the pcb is >= 48mm
also heater is 12,6v
grille design is important, too.
the apex460 is probably more suited for a C12-ish capsule/tube/transformer

look at the description of the t-bone sct700 for reference.
dimensions / Maße: 58.5 mm x 180mm
http://www.thomann.de/at/the_tbone_sct700_roehrenmikrofon.htm

edit: the nady 1050 seems to use the same housing