Official C12 Clone - Build and Support Thread

[HellfireStudios]

Hi,

I'm really happy with these C12, but I'm wondering if some Deoxit applied on the tube pins (which are a little bit oxydated, 50 years old nos) might improve the signal/noise ratio?

I currently have deoxit d100L, but I was about to buy deoxit gold, which seems to be better for this application (no lubricant I believe).

What is your opinion?

Thanks,

Rémi

DeOxit Gold is for gold plated connectors. Regular DeOxit is for the the other types of connectors, pots, etc.

It couldn't hurt to try it out, but a google search about using DeOxit on a tube wouldn't hurt either (to avoid any mishaps). Let us know how it goes for you.

-James-

 

[Matador]

Hi,

I'm really happy with these C12, but I'm wondering if some Deoxit applied on the tube pins (which are a little bit oxydated, 50 years old nos) might improve the signal/noise ratio?

I currently have deoxit d100L, but I was about to buy deoxit gold, which seems to be better for this application (no lubricant I believe).

What is your opinion?

Thanks,

Rémi

What exactly do you mean by "improve"?  Is it too quiet?  Too much background hiss?  To little capsule signal?

Before you do anything else, did you make sure you scrubbed the area around the capsule connections on the PCB with good quality IPA?  This area needs to be clean and free of solder flux.

 

[cariocaman85]

I explain myself:

The mics are both fonctionning very well, we did a great piano record few days ago.

But one of the mic had a few crackles, and intermittent hiss on last monday, so I was worried about the tube. I opened the mike, removed the tube, then replaced it, and everything went fine. But yesterday, the same thing happened so I started again the procedure, but without good results. When I gently touched the body I clearly could hear bad contacts, and crackles.

So this morning I retensioned the socket which I believe was a little bit to much loosen during the building, then I replaced the tube and it went fine, no more crackle nor hiss.
So It appears that it solved my problem.

By the way I noticed some oxydation along the tube pins, which I believe it's normal for a 50 years old tube, but I was in the process of troubleshooting this crackles and I thought about removing this oxydation in order to get a better contact.

That's why I'm wondering if deoxit might improve this connection between the tube and the socket. The PCB is absolutly clean of flux, we were very carreful during the building of the mic.
As I looked since this minute every forum on the web to find a clear answer to this question, I noticed that deoxit gold is designed to improve tube to socket contact dixit the manufacter (high temps rates and every metal connexion).
But apparently some people recommand it, and some don't. That's why I'm a bit confused.

So for the moment I have 2 mikes working perfecly. I hope it will last 

Thanks for your comments,

Best,

Rémi

 

[originalmusician]

About how many AC volts should I get at the 200v connector shown in the attached picture when measured in circuit?

 

[Matador]

About how many AC volts should I get at the 200v connector shown in the attached picture when measured in circuit?

You should get 200*SQRT(2) = ~280V across the two terminals.

 

[chunger]

I explain myself:

The mics are both fonctionning very well, we did a great piano record few days ago.

But one of the mic had a few crackles, and intermittent hiss on last monday, so I was worried about the tube. I opened the mike, removed the tube, then replaced it, and everything went fine. But yesterday, the same thing happened so I started again the procedure, but without good results. When I gently touched the body I clearly could hear bad contacts, and crackles.

So this morning I retensioned the socket which I believe was a little bit to much loosen during the building, then I replaced the tube and it went fine, no more crackle nor hiss.
So It appears that it solved my problem.

By the way I noticed some oxydation along the tube pins, which I believe it's normal for a 50 years old tube, but I was in the process of troubleshooting this crackles and I thought about removing this oxydation in order to get a better contact.

That's why I'm wondering if deoxit might improve this connection between the tube and the socket. The PCB is absolutly clean of flux, we were very carreful during the building of the mic.
As I looked since this minute every forum on the web to find a clear answer to this question, I noticed that deoxit gold is designed to improve tube to socket contact dixit the manufacter (high temps rates and every metal connexion).
But apparently some people recommand it, and some don't. That's why I'm a bit confused.

So for the moment I have 2 mikes working perfecly. I hope it will last 

Thanks for your comments,

Best,

Rémi

For what its worth, I user deoxit on matador's first prototype build when I put a nos ge 6072a in for testing.  I used it primarily to lube the pins because the socket was so tight.  There were no ill effects.

 

[originalmusician]

About how many AC volts should I get at the 200v connector shown in the attached picture when measured in circuit?

You should get 200*SQRT(2) = ~280V across the two terminals.

Thanks Matador!

I just bought a used Fluke 87V of Ebay because my el cheapo Harbor Freight meter appears to finally have given up the ghost and be spitting out whack readings in AC mode.

http://www.ebay.com/itm/Fluke-87V-TRMS-Digital-Multimeter-/141063307290?ssPageName=ADME%3AL%3AOC%3AUS%3A3160&nma=true&si=ajvyb1JvHX5QOXh17x7EIC3561k%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Since the Fluke is used and of unknown history, I was a little concerned about it being accurate. So I put in a new battery, set the meter to Ohms mode, plugged a lead into the Ohms jack, and carefully touched the ohms probe tip to the top of the the mA/uA output jack. This bypassed the LEAD alarm and gave me a reading of 1.000K Ohms. Apparently, this measures the reference voltage and part of the precision resistor network, and it is spot on for this meter.

I was trying to figure out a good test of the AC function, and after work tonight, my neighbor stopped by with a CircuitSpecialist.com meter. Both meters tested ~240V across the transformer winding. I'm guessing this is a realistic real world measurement vs. the theoretical measurement you provided that is free from inefficiencies and losses.

I think my new meter is good to go! 

 

[Matador]

Yeah, 280 assumes no current draw....sorry I should have specified that.  But 240 before the rectification sounds a tad low, but if you can trim out the B+ voltage I wouldn't worry about it.

 

[Reverend]

180k resistor is still in. So, for #1) do I touch black from my DMM to the ground and the red to the lead coming off of the resistor R1 towards C1?
#2) Black on ground and red on the lead coming off of R1 going toward C2?

Ground always stays ground.  If black is ground, and red is your test probe, then touch it in sequence at the places I mentioned above.

OK. I understand the black to ground thing. Should I touch the red to the lead coming out of the resistor R1 on the side going to C2? And so forth? Thanks and sorry.

That's right.

1) R1 and C1  Not getting a good reading. It flashes several different readings but very quickly goes to 1 (left side 1 on DMM read out) and stays there.
2) R1 and C2 Same thing as #1...no real reading 196 for a split second then back to one
    R2 and C2  no real reading.....one
3) R2 and C3  no real reading...one
    R4 and C3  no real reading again except when I touch the top of the trim pot (R4), it goes to zeros

One more thing. R5 to C5 - 1.2
Heater 6.3
Bias -1.1

 

[Christopher L]

Thanks Chunger and Matador for such a fun diy project.  I have a working mic, but one that is a bit noisy.  When replacing the stock capsule with Tim's I damaged one of the 5000pf capacitors by touching my iron against it a bit.  I found some on ebay but with 160v rating(will this work), this was not the culprit.  All my measurements are correct except the bias fluctuates so much that I'm unable to get the -1.0v. Testing the mic last night there were times when I heard a pop and one time the mic completely cut off for a second or two.  Should the two ground traces on the psu be connected to something. Please help.

 

[Matador]

1) R1 and C1  Not getting a good reading. It flashes several different readings but very quickly goes to 1 (left side 1 on DMM read out) and stays there.
2) R1 and C2 Same thing as #1...no real reading 196 for a split second then back to one
    R2 and C2  no real reading.....one
3) R2 and C3  no real reading...one
    R4 and C3  no real reading again except when I touch the top of the trim pot (R4), it goes to zeros

One more thing. R5 to C5 - 1.2
Heater 6.3
Bias -1.1

That behaves like a meter that is over it's limit.

What's the max voltage the meter can read on it's DC setting?  It's often printed right on the meter itself.

I'm guessing 200V. 

 

[Reverend]

1) R1 and C1  Not getting a good reading. It flashes several different readings but very quickly goes to 1 (left side 1 on DMM read out) and stays there.
2) R1 and C2 Same thing as #1...no real reading 196 for a split second then back to one
    R2 and C2  no real reading.....one
3) R2 and C3  no real reading...one
    R4 and C3  no real reading again except when I touch the top of the trim pot (R4), it goes to zeros

One more thing. R5 to C5 - 1.2
Heater 6.3
Bias -1.1

That behaves like a meter that is over it's limit.

What's the max voltage the meter can read on it's DC setting?  It's often printed right on the meter itself.

I'm guessing 200V. 

For those readings, I had it set on 200V for all. There is a 600 setting. Here's my results measuring on the 600V setting.

1) R1 and C1 ....300V
2) R1 and C2 .....242V
    R2 and C2 .....252
3) R2 and C3......208
    R4 and C3......not sure how to take this reading. Touching the top of the trim pot, 000

Thanks for walking me through this.

 

[kcatthedog]

hi, i have a new mastech ms8268.  I am trying to test the AMI T14 transformer. i am using the pairs of reds and blue wires separately as the pictures but the readings never stabilize.  i have the metre set for ohms and it has an auto ranging function.

i am working on the mike. I took the pcp for the power supply to a tech to diagnose. He confirmed my solders were good, so I am curious to learn what I did wrong to explain incorrect variable resister readings ?


thanks ,

kcat

 

[brewbacca]

Hi there, I have a couple of these I'm trying to do, but I'm a little confused about some of the readings I'm getting off the power supplies, and want to make sure those are ok before moving onto the microphones.

In the picture you can see that I'm trying to check the power transformer's voltage, and on both I'm getting around 6-7V on each of the 9.5V terminals, and around 110V on each of the 200V terminals. It this normal? I checked the second power transformer before modding the power supply and was getting similar reading at that point. Also, when I check B+ the voltage starts around 100V on each and climbs to around 210V over the course of a minute or two. Is that normal? This is the first power supply I've modded so I'm kind of a newbie about voltage, although I know not to touch anything with my hands that isn't made out of rubber

Thanks!

 

[originalmusician]

Hi there, I have a couple of these I'm trying to do, but I'm a little confused about some of the readings I'm getting off the power supplies, and want to make sure those are ok before moving onto the microphones.

In the picture you can see that I'm trying to check the power transformer's voltage, and on both I'm getting around 6-7V on each of the 9.5V terminals, and around 110V on each of the 200V terminals. It this normal? I checked the second power transformer before modding the power supply and was getting similar reading at that point. Also, when I check B+ the voltage starts around 100V on each and climbs to around 210V over the course of a minute or two. Is that normal? This is the first power supply I've modded so I'm kind of a newbie about voltage, although I know not to touch anything with my hands that isn't made out of rubber

Thanks!

You are measuring the transformer incorrectly. You need to touch your negative meter probe to one blue wire connector and touch the positive probe to the other blue wire connector. That should give you somewhere around 250vac. Then use your meter probes to jump across the yellow transformer wires in a similar manner. For this, you should get somewhere around the 10v.

Post back with your readings.

I got a similar slow reading to you when I checked my B+. I'm unsure of the explanation of why this occurs.

 

[brewbacca]

Ah! Ok, those readings are much better (~212V and ~11V).  Thanks for the heads up!

 

[Matador]

Yes if you ground the negative probe and then touch each primary, you are only getting half the winding (wrt ground).  Measuring across the secondary will show you what you are testing for.

Remember that we derive the ground by referencing the split between the rectifier diodes:  hence we can only ever measure one half of the AC signal on our meter.

Stealing a Wikipedia image:

If you measure right across the secondary, your meter will see the full signal swing just like the right side of the picture.  If you ground the meter, your meter will only see the rectified peaks which is exactly half of the peak-to-peak swing.

 

[originalmusician]

Ah! Ok, those readings are much better (~212V and ~11V).  Thanks for the heads up!

Interesting.

My mic PS came with the same alternate transformer as you (the windings are reversed compared to the one in Chunger's photos). I got ~242v and 11.4v readings. With these values, the variable resistors allowed for plenty of adjustment on either side of the B+ target  (120v) when I put a 180K resistor across B+ and ground.

 

[Matador]

1) R1 and C1 ....300V
2) R1 and C2 .....242V
    R2 and C2 .....252
3) R2 and C3......208
    R4 and C3......not sure how to take this reading. Touching the top of the trim pot, 000

Thanks for walking me through this.

Hmmm...R1, R2, and C2 are all the same node:  why you measure 242V then 252V is odd.

So you are dropping 50V across R1 which (is supposed to be) 91K, which means there is 0.55mA flowing through R1.  You loose another 45-50V across R2 which is consistent with 0.55mA flow.

Can you tell me what the printing is on the top of R4?  It's behaving like the wrong trim pot is installed in there (like several have done previous in the thread).

 

[Reverend]

1) R1 and C1 ....300V
2) R1 and C2 .....242V
    R2 and C2 .....252
3) R2 and C3......208
    R4 and C3......not sure how to take this reading. Touching the top of the trim pot, 000

Thanks for walking me through this.

I took great care in making sure that I got each component in  right and followed directions to a t.
That being said I still could have made mistakes of course. Ha Ha.
My trim pot still doesn't change the voltage value .....can't be adjusted.
Thanks and sorry for the confusion. Still having fun...but I want to use this mic on my session this week....probably not possible now, but I would appreciate your help. My plan was to build two of these, but now, I had better focus on just one.

Hmmm...R1, R2, and C2 are all the same node:  why you measure 242V then 252V is odd.

So you are dropping 50V across R1 which (is supposed to be) 91K, which means there is 0.55mA flowing through R1.  You loose another 45-50V across R2 which is consistent with 0.55mA flow.

Can you tell me what the printing is on the top of R4?  It's behaving like the wrong trim pot is installed in there (like several have done previous in the thread).

Wow. On the blueprint of the pcb for the power supply, there is an R4 resistor where, on my pcb, and in the pictures, that's where the B+ adjust trim pot goes. Confusing. I would not have put the trim pot there except that it's that way it is on my pcb, with the dotted line around the B+ adjust and all.
So, is my power supply ok? Still not getting the trim pot in the B+/R4/whatever to adjust the voltage.