Anyone know the B+ for a Sony C37A Mic

[gary o]

Just fiddling with this Sony C37A circuit using 120V HT anyone know what it should be ?...thanks

 

[rodabod]

There was an analysis here recently which you might want to search for.

 

[gary o]

Thanks Roda, yeah I did search before read all I could find may have missed something its seems the guess is about 230V... higher than usual......mine works ok with 120V and a solid tubes electret capsule but low output & crap sound when I connect my Violet capsule {Vin 67 meant to be like a U67}...I wonder if it would come alive with higher HT ...I dont want to hurt my Violet tho...maybe I can inch the power up slowly....

Cheers

 

[gary o]

Update......more fiddlings..........Im running my DIY C37A at 120V B+ I have a large mic pre transformer unidentified but similar in size & sound (in a mic pre) as my Sowter 9045 ( quite expensive) I have no 10K res across the OP unlike in the C37 schematic its sounds really nice with either Violet Vin67 lolly (expensive) or my Oktava MK101 head can make up mind which is best like em both just different which makes me wanna add that for the money I love the okt MK101 bargin !!! its same capsule inc resonator disc as the 219/319

the over all level is lower than the transformerless MK012 mic I got with the MK101 head .......the C37 & Mk012 sound quite sinilar with the MK101 head

Im very happy with the C37A & may even make a better case for it ....at mo it life is a cat food tin

 

[lassoharp]

Im very happy with the C37A & may even make a better case for it ....at mo it life is a cat food tin

pics for posterity?

sounds like a must see!

 

[Gus]

It reads like you need to readjust the tube operating points.

What is the voltage at the "bottom" and "top"of the 3K(sony schematic bias resistor)?  That is going to be close to the capsule voltage.

You will need to balance the capsule charge voltage and the plate current and the cathode resistor values to the 120V B+
You want to find a spot on the curves so you have say 65VDC(just picked this as a voltage) or so at the cathode.
Lets say you want 1ma plate current at 65VDC you will want a 65K(use a 68K) in place of the 100K AND you will need to adjust the 3K value so the tube conducts 1ma.  I picked 1ma for easy math.

 

[maxwall]

Gary O

would it be possible to get detailed pics from inside the C37 power supply ?

I have been looking for pictures for a while, no luck yet. need to contruct a psu
for a mic which does not have one. Want to get an idea of layout etc....

any help aprreciated.  pics fowarded to

email : electrochronic(at)ymail(dot)com

 

[gary o]

Electrochronic....hi sorry but I dont have a REAL C37 PSU Im just hacking things together out of junk really, Im using for B+ a simple PSU I built to power tube mic pres and compressors, it happens to be similar to the C37a B+ circuit, I wasnt sure of the correct B+ voltage tho it is here somewhere so Im using 120V at the moment.....for LT Im using a separate  LM317 adjustable supply at 6.3VDC .....

I see the C37 PSU does something a little different with its LT .....I dont fully understand how that part works maybe to do with lower noise...maybe a smart chap can tell whats going on their.....

I think it would be cheap and easy to build point to point playing by the usual layout rules....

heres some info about resistors for PSU....and more
http://www.groupdiy.com/index.php?topic=153.0

Lasso il see if I can take a pic of the Catfood mic, I know my messy creations make some of you laugh & Im pleased it does .....my goals are to hear old designs & parts in the cheapest quickest way possible & to learn as I go, any thing I really like the sound of may get re homed, this mic may even get to live in a chocolate tin next.....

Gus thanks for your pointers ...I must apologise I dont understand electronics as well as most here so Im finding it hard to follow what you are saying.....I can measure the 3K top/bot tho ......I could feed the mic any B+ if 120VDC is no good ....tho the mic sounds good to me as is at moment....I must look up the C37a B+ I no its in a thread here......

 

[lassoharp]

Lasso il see if I can take a pic of the Catfood mic, I know my messy creations make some of you laugh & Im pleased it does .....my goals are to hear old designs & parts in the cheapest quickest way possible & to learn as I go, any thing I really like the sound of may get re homed, this mic may even get to live in a chocolate tin next.....

I love the DIY ingenuity and catfood tin for hi $ mic capsule housing is priceless.  I regularly use rusty nuts & drinking straw sections for turret board spacers.  I'm cheering for you. 


 

 

[argibbo]

Hi Guys
I have built a C37a replica and tube rectified power supply. I couldn't find the plate voltage on the original Sony schematic. Did anyone manage to find out the original manufacturer specified value?
Thanks
Andy

 

[Matt Nolan]

Hi Guys
I have built a C37a replica and tube rectified power supply. I couldn't find the plate voltage on the original Sony schematic. Did anyone manage to find out the original manufacturer specified value?
Thanks
Andy

The B+ on the C37a is a surprisingly high 210V.

Depending on which version of the mic and psu you are building (there are 2, both mics called C37a, but with different named PSUs - CP-2, CP-3B) you need to make sure that the heater elevation matches the cathode voltage. The mics differ in bias set up and capsule polarisation (just about 1.4V under the cathode). The older version has the cathode at B+ * 1/2, the later version is at B+ * 2/3.

Of course, unless you are using a genuine Sony capsule, or an accurate copy, you're not going to be able to use such a high capsule polarisation voltage, so you'll have to make some changes.

Cheers,
Matt.

 

[chops]

The B+ on the C37a is a surprisingly high 210V.

Depending on which version of the mic and psu you are building (there are 2, both mics called C37a, but with different named PSUs - CP-2, CP-3B) you need to make sure that the heater elevation matches the cathode voltage. The mics differ in bias set up and capsule polarisation (just about 1.4V under the cathode). The older version has the cathode at B+ * 1/2, the later version is at B+ * 2/3.

Of course, unless you are using a genuine Sony capsule, or an accurate copy, you're not going to be able to use such a high capsule polarisation voltage, so you'll have to make some changes.

Cheers,
Matt.

Sorry to dredge up an old thread. but I just picked up a "pair" of Sony C37a's.  One has the CP2 PSU and the other has the CP3b PSU.  Do you mean there are actual differences in the microphones themselves?    If so, can you help me sort out which mic belongs to which supply? 

 

[chops]

Just comparing the schematics I see that R2 inside the microphone is 3k for mics connected to the CP2 and 1k for the CP3b.  I guess that should be the clue...  Any other secrets about these mics/PSU's?