Morelius21

problem whit ELA M 251E
« on: June 12, 2019, 06:22:36 AM »
Hi

i have a this mic and there are a component that i don't know what is it.

the first picture you can see the position in the mic section. The part is the first, begin in the left section


 

then the part



the colors are:

Green  Black  Violet         Yellow Black

A resistor can't be because there arnt tolerance black

A inductor whit five bands , the first must be silver.

A Capacitor maybe?

Any help please.

thanks for advance


Khron

Re: problem whit ELA M 251E
« Reply #1 on: June 12, 2019, 06:38:45 AM »
Can you measure it with an ohmmeter?

At least comparing the first photo with the schematic, and if my circuit node guesses are correct, that might(?) be (at least originally) the 30Meg resistor, between the triode gate and ground.

I *think* that white wire, from the lowest "pin" in the first photo, should go to the triode gate.  The bottom end of that fat silver 10nF cap should be connected to ground, and through the jumper-wire next to it, so should the "top" end of that "mystery" resistor.

More importantly though, what exactly are the symptoms?
« Last Edit: June 12, 2019, 06:47:09 AM by Khron »
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Morelius21

Re: problem whit ELA M 251E
« Reply #2 on: June 12, 2019, 09:29:05 AM »
Hi

The problem is that the sound is smaller than other mic the same model. 

When i try to mesure with my fluke meter in ohm and capacitance position or my cheap inductance meter the result is nothing or damage. 

this part go to pin 7 of the tube 12ay7 and the capsule. Whit the schema must be a resistor 30Megh o 8 Megh but the problem is that i don't understand the color code.

Thanks

Khron

Re: problem whit ELA M 251E
« Reply #3 on: June 12, 2019, 10:51:57 AM »
Pin 7 is indeed one of the triode grids.

http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12AX7.pdf

Depending on what model your multimeter is, it might not be able to measure values that high - often the handheld ones top out around 2Meg or 10Meg.

Judging by the connections, that should be indeed the 30Meg one.

Either way, unless that resistor somehow lost value (ie. its value went down, by a LOT), that shouldn't really affect anything. Plus most often, when resistors fail, they fail open-circuit.

What's the "B+" voltage, coming from the power supply? You should be able to measure that between the common connection of the 100K resistor and one of the 499K ones (2nd and 3rd black resistors, counting from the left), and ground.
Around 110V DC is what we're expecting.

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Re: problem whit ELA M 251E
« Reply #4 on: June 12, 2019, 11:17:11 AM »
If you read as 4-band it's 50MΩ 5%.

Looks like 3rd band is blue. Violet would be 500MΩ.

In this position you can use anything from 30M to 250M with good results. Use higher values for more lowend.


 

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