Melos Tape Echo replacement lamp/LED?

1990mz
New Member

Posts: 1

Melos Tape Echo replacement lamp/LED? Apr 20, 2018 7:39:40 GMT -6

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Post by 1990mz on Apr 20, 2018 7:39:40 GMT -6

Hi all,

I recently acquired a fairly cheap Analog Tape Delay, the Melos Echo Chamber, and thought it might be a good starting point for a basic DIY project. I've disassembled it, cleaned it and am in the process now of trying to make it look 'nice' and find a replacement power lamp/LED indicator for the front panel.

I have searched to no avail regarding matching voltages and current types (unless someone can point me in the right direction - in which case I apologise) but am no closer in understanding what I require. So my two questions (to start with) are:

1. How can I ascertain what voltage the lamp should be? I basically have two terminal wires ready for a bulb, so is it a case of buying a meter reading and working out from that what the current draw is, or am I completely missing some fundamental law of electronics here. The options I've seen that look suitable range from 12v to 24v to 220-240v. I'm operating off a UK 240V mains.

2. Assuming i can fit an LED replacement instead, do I need to take into account other variables like resistors etc? If so what should I look out for? Originally this had a very small bulb (bayonet?) attached, inside a standard metal housing, but unfortunately it got destroyed whilst taking the units face-plate off. There were no markings on the bulb or fitting denoting it's voltage rating.

I am pretty ignorant when it comes to these things, and will try and brush up on some basic electronic know-how, but I thought i'd post here in the meantime in case anyone out there could offer some guidance or advice as to what to I should look out for, or what questions I should be asking.

I really appreciate any help!

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johneppstein
RGO Senior Member

Posts: 5,328

Melos Tape Echo replacement lamp/LED? Apr 20, 2018 12:48:28 GMT -6

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Post by johneppstein on Apr 20, 2018 12:48:28 GMT -6

Apr 20, 2018 7:39:40 GMT -6 1990mz said:

Hi all,

I recently acquired a fairly cheap Analog Tape Delay, the Melos Echo Chamber, and thought it might be a good starting point for a basic DIY project. I've disassembled it, cleaned it and am in the process now of trying to make it look 'nice' and find a replacement power lamp/LED indicator for the front panel.

I have searched to no avail regarding matching voltages and current types (unless someone can point me in the right direction - in which case I apologise) but am no closer in understanding what I require. So my two questions (to start with) are:

1. How can I ascertain what voltage the lamp should be? I basically have two terminal wires ready for a bulb, so is it a case of buying a meter reading and working out from that what the current draw is, or am I completely missing some fundamental law of electronics here. The options I've seen that look suitable range from 12v to 24v to 220-240v. I'm operating off a UK 240V mains.

2. Assuming i can fit an LED replacement instead, do I need to take into account other variables like resistors etc? If so what should I look out for? Originally this had a very small bulb (bayonet?) attached, inside a standard metal housing, but unfortunately it got destroyed whilst taking the units face-plate off. There were no markings on the bulb or fitting denoting it's voltage rating.

I am pretty ignorant when it comes to these things, and will try and brush up on some basic electronic know-how, but I thought i'd post here in the meantime in case anyone out there could offer some guidance or advice as to what to I should look out for, or what questions I should be asking.

I really appreciate any help!

That echo looks suspiciously like the Univox echo I'm in the process of buying from Svart - my guess it's the same with a differrent faceplate. You might ask him if he has any idea.

A few general suggestions - Check the voltage on the two wires with a voltmeter. That should put you in the ballpark. The size of the mounting bezel makes me suspect that it might be an NE-2 miniature neon bulb, but I can't be certain Depending on the exact type, NE-2 bulbs run on between 65VAC and 95VAC so you'd probably need a dropping resistor. If you converted it to an LED you'd DEFINITELY need some sort of resistor for current limiting and possibly voltage adjustment. If the voltage is high you'd need a circuit to knock the voltrage down to something an LED could handle, or take a feed off a different part of the circuit.

Try tracing the two wires back to see where they come from, if it's the AC line (through the power switch of course), the power transformer, or somewhere in the circuitry. NE-2s were sometimes used in oscillator circuits so it could be part of the bias, but that's just a guess. If it is, the machine won't record or erase without it.

NE-2s nearly always have an inline resisitor if they're straight off the powerr line. They'rer a small, pointed glass bulb with two bare wires out the base and generally slips into some sort of bezel. You mentioned you thought it might have been a bayonet mount - if so it's not an NE-2 and it could be anything.

EDIT: Do you have any pics of the circuit board? I found a couple of promising looking schematics but need to determine a bit about the circuit - one uses ICs and had an LED, the other uses discrete transistors and uses an NE-2 type neon.

Last Edit: Apr 20, 2018 13:24:22 GMT -6 by johneppstein

svart
RGO Senior Member

Sewer Robot

Posts: 10,146

Melos Tape Echo replacement lamp/LED? Apr 20, 2018 13:56:47 GMT -6

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Post by svart on Apr 20, 2018 13:56:47 GMT -6

Yes the Univox EC100 is a red LED.

The one in that picture above is a LED as well from the looks of it.

LEDs usually live in the realm of 1-5 volts, but are direct current driven devices (only the current value matters to the LED as long as the voltage is not too high). What you need to know to figure out how to replace the LED is the supply voltage where the original LED is hooked to, and the specs of the LED you want to use such as the maximum voltage and the current you need to run the device.

Then it's ohms law and a little math.

You need to figure out the voltage drop using the source voltage minus the voltage of the LED and then divide by the current of the LED.

So lets say it's 12V as the source, and the LED is 2V @ 20mA.

12-2=10/0.02A=500 ohms.

To use a 2V/20mA LED at 12 volts, you'd put a 500 ohm resistor in series with it.

They make panel-mount LEDs for common voltages like 12VDC, 24VDC, etc.. So if you have a source voltage like that, you could just buy one..

Also, I found a pic of one which seems to have an LED, but I don't know if LEDs were stock.

Last Edit: Apr 20, 2018 14:03:04 GMT -6 by svart

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