Original Urei 1178 (Rev H) - Changing VU Bulbs/Lamps

Whoops · Mar 8, 2018

Hello,
I'm servicing at the moment an Urei 1178 unit, one VU meter had 2 failed bulbs. (each VU has two Bulbs in series)

I bought the unit second hand and all the bulbs were dead, it came with type CI 382 , 14V 80mA , T1 3/4 6mm miniature Flange Base.
although the schematic says Type 387, CM387, 28V, 40mA

I bought replacements from Ebay, you can also buy from Studio Electronics store.
The Ebay replacements were Type 387

While searching for the lamps I came across some opinions on other forum that there's a notion the 1176 and 1178 compressor sound better without the lamps (subjective) or at least that the lamps have a negative impact on performance of the unit since they are draining unregulated power (AC) from the same PSU as the circuit and before the audio circuit rails.

here is the PSU schematic

I have no problems in changing/converting the VU lightning for LEDS, neither does the unit owner, in case needed.
It can also be easily changed in a completely reversible way

So I would like to humbly ask your opinion and personal experience with the original units?
Is the Lamp degrading the sound a myth or is it something to consider?

thank you so much

radardoug · Mar 8, 2018

Its a myth. Use LEDs if you want, saves power and they last longer.

PRR · Mar 9, 2018

> unregulated power (AC)

Worse: they carry half-wave power. Perhaps around sensitive circuits?

This is the 21st century. Four white LEDs in series amounts to about 16V. Steal the exact connection shown for DS5 "Power" LED. 10mA may be plenty. You have 20V to spare. Series resistor is 2.2K 1/2W.

Whoops · Mar 10, 2018

Thank you so much for your reply PRR

PRR said:
> unregulated power (AC)

Worse: they carry half-wave power. Perhaps around sensitive circuits?

Could you please explain a bit more?
Are you referring to possible noise inductions into the circuit from the wires that take the Half wave power to the VU Lamps?

So the problem people refer to might not be the Power consumption of the Bulbs but noise induction?

PRR said:
This is the 21st century. Four white LEDs in series amounts to about 16V. Steal the exact connection shown for DS5 "Power" LED. 10mA may be plenty. You have 20V to spare. Series resistor is 2.2K 1/2W.

So I put 4 LEDs in series with the DS5 power led, making it 5 LEDs in series and then change R80 to 2.2K?

Thank you so much