MK47 PCB tube mic kit - build thread

[Monoklang]

Thinking about it, it is not clear how many separate wires you have in your cable.  I was assuming that you have 7, but if you only have 6 core cable, I advise using pin 7 instead of pin 3 for the reason I stated.

The cable I will use is this one:
http://www.thomann.de/se/sommer_cable_sc_octave_tube.htm

So there is 7 wires but 2 of them is thicker (twisted in picture). Good for ground?

To advise on where the return goes I would need to know the model of transformer you are using.

This is the torodial I will be using:
http://www.tube-town.net/ttstore/product_info.php/info/p2192_Torodial-30VA.html

The light you have chosen is likely to be much brighter than you want.  I would have advised an LED with a resistor in series to reduce the brightness: 390 ohms would be a good start with a red LED. This can be increased in value to lessen the brightness.

David

This doesn't look to be too bright I think, but I guess I will find out and can switch to LED if that's the case.
http://angela.com/fenderredpilotlightjewelforguitaramps.aspx

Thank You!
/ John

 

[david-p]

The cable I will use is this one:
http://www.thomann.de/se/sommer_cable_sc_octave_tube.htm

So there is 7 wires but 2 of them is thicker (twisted in picture). Good for ground?

As I understand it, like the U47, you have only one supply for this design, and both the HT and the valve heater are powered off it.  Use the two fat wires for B+ and ground (pin 7!).

This is the torodial I will be using:
http://www.tube-town.net/ttstore/product_info.php/info/p2192_Torodial-30VA.html

OK: use the two green wires for the light.  Twist them together, but dont ground either of them.

David

 

[Songguy]

Quick PSU question..

If I opt to use the 6.3v tap on my trafo do I need to install the 100k 1w resistor?

 

[wave]

Quick PSU question..

If I opt to use the 6.3v tap on my trafo do I need to install the 100k 1w resistor?

If you are using the 6.3 VAC tap for a jewel light and not using a LED then you still need the 100K resistor as a bleeder for the cap. You will have to jumper where the LED is

Dave

 

[0dbfs]

Quick PSU question..

If I opt to use the 6.3v tap on my trafo do I need to install the 100k 1w resistor?

If you are using the 6.3 VAC tap for a jewel light and not using a LED then you still need the 100K resistor as a bleeder for the cap. You will have to jumper where the LED is

Dave

Even so, having the led installed is a nice visual to confirm the caps are drained before proceeding with work. The jewel lamp will extinguish when ac mains are off. Led would stay lit for a couple minutes.

This is what I have experienced.

Cheers,
Jb

 

[wave]

Quick PSU question..

If I opt to use the 6.3v tap on my trafo do I need to install the 100k 1w resistor?

If you are using the 6.3 VAC tap for a jewel light and not using a LED then you still need the 100K resistor as a bleeder for the cap. You will have to jumper where the LED is

Dave

Even so, having the led installed is a nice visual to confirm the caps are drained before proceeding with work. The jewel lamp will extinguish when ac mains are off. Led would stay lit for a couple minutes.

This is what I have experienced.

Cheers,
Jb

Very true. I was kinda assuming he wasn't even sourcing the LED.

Dave

 

[Songguy]

Thanks for the clarification folks.

Btw I couldn't find a 2.3k 5w res. I did find a 2.25k and a 2.4k 5w. Would either of these be an acceptable replacement?

 

[mrvision]

For the 2.3k test load resistor here in America I used a 1.1k and a 1.2k in series

Mouser:

594-AC05W1K100J
594-AC05W1K200J

Btw the 2.3k resistor is for testing and initial setup only, you have to readjust voltages once you have the microphone connected to the psu. In my case I first adjusted the voltage to 105V with the 2.3k dummy load, then with the real load (mic) the voltage was 109V, then readjusted the voltage again to 105V and closed the psu box.

 

[Songguy]

So with the mic hooked up you had to swap that 2.3k with a resistor that would give you 106v?

Also I'm having a real hard time finding a 14k 1w res. does this need to be a metal film res. or is there another more available type I could use.
Thanks for your help with this.
Chris

 

[david-p]

I'm having a real hard time finding a 14k 1w res. does this need to be a metal film res. or is there another more available type I could use.

Chris,

27k in parallel with 30k, 1/2 watt each, or 4x56k 1/4 in parallel.  I find it a useful trick to share the wattage in this way.

David

 

[kante1603]

So with the mic hooked up you had to swap that 2.3k with a resistor that would give you 106v?

Hi Chris,

no-look at the schemo:The "test"-switch is for giving the psu a load similar to the connected mic by switching in this 2,3k/5w resistor
before!!! you connect the mic.This is to proof your psu is working before killing your beloved microphone.
If everything is measuring fine with the switched-in resistor power down your psu,then switch off the resitor,then connect the microphone and do a final measurement/adjustment of the B+.
In my case I even did not use a switch,just a piece of solid core wire attached to 2 screw terminals which are labelled "test".

Also I'm having a real hard time finding a 14k 1w res. does this need to be a metal film res. or is there another more available type I could use.

I used 2 pieces of 28k in parallel,as far as  I can remember I found them at mouser....
This 14k is just a voltage divider together with the 12k to get the approx. +48vdc from the B+ to drive the relay and nothing else.

O.K.,did a quick search at mouser,found them:
http://de.mouser.com/ProductDetail/Vishay-Dale/CPF128K000FEB14/?qs=sGAEpiMZZMukHu%252bjC5l7YcnhMAGkDTDNt9nRJOdArgk%3d

Hope to have helped,

Udo.

 

[mrvision]

For the 14K resistor I used a 12K + 2K in series, both 1W.

bought two 12K and one 2K from Mouser:

(1) 2K:    660-MO1CT52R202J
(2) 12K:  660-MO1CT52R123J

 

[mrvision]

Also the 2.3K Test Resistor can be a little confusing. Specially for those of you initianting in electronics or DIY.
In the original schematic the 2.3K "test" resistor is shown inside the circuit, I personally did not include it in the circuit because the resistor has shown a little discrepancy of about 3-4 volts, If you read the thread there are some others that also found different readings with the real load, The 2.3K only tells you if the PSU is giving the juice is suppose to give and also gives you a close voltage to the one needed by your microphone.

I also recommend taking the time to read the thread, there is a lot of information already there. When you find a problem you already have an idea where to find some troubleshooting information 

The schematic below shows the 2.3K taken out of the circuit and used externally during test.

 

[0dbfs]

I'm pretty sure I left this feature out when I did mine. You need to tweak/fine-tune it with mic in-circuit anyway.

Plus, what are you going to fry in the mic? Some resistors, the tubes? If you are worried about your capsule, put in a couple capacitors until you have voltages and things all tweaked.

Cheers,
jb

 

[kante1603]

Also the 2.3K Test Resistor can be a little confusing. Specially for those of you initianting in electronics or DIY.
In the Schematic is shown inside the circuit, I personally did not include it in the circuit because the resistor has shown a little discrepancy of about 3-4 volts, If you read the thread there are some others that also found different readings with the real load, The 2.3K only tells you if the PSU is giving the juice is suppose to give and also gives you a close voltage to the one needed by your microphone.

I also recommend taking the time to read the thread, there is a lot of information already there. When you find a problem you already have an idea where to find some troubleshooting information 

+1!

 

[Songguy]

Thanks for the clarification. I have read the thread and bookmarked various posts and replys. I just require a little assistance understanding who the sum of the parts work together as a whole.
Thank you for your patience and sharing your experiences with me.
Chris

 

[Songguy]

Ok guys, I need one more piece before I put this psu together. Does anyone have any preferences when it comes to a pattern switch? Rudimentery question but curious none the less.

 

[wave]

Ok guys, I need one more piece before I put this psu together. Does anyone have any preferences when it comes to a pattern switch? Rudimentery question but curious none the less.

I used this just because it's big and awesome

http://www.mouser.com/Search/ProductDetail.aspx?R=S2B-ROvirtualkey63300000virtualkey633-S2B-RO

Dave

 

[Songguy]

An excellent choice Dave. I just placed an order for the same one. looks like one substantial switch.

 

[wave]

An excellent choice Dave. I just placed an order for the same one. looks like one substantial switch.

It's beefy. That's a quarter!

Dave