Hi I just got an EICO 378 signal generator and it worked great until the other day then I discovered that the little light bulb had burned out inside. It is a 3W 120V and "I'd like to know what it's for" as I have no schem and it definately isn't an on off light.. as it's inside the chassis near a 6au6. Anyway I replaced it with a Christmas bulb 120V but 5W instead if the orig 3W and It works but the wave isn't nicely simetrical as before, the top is slightly pointed?? but near perfect and I wonder if it is the bulb higher wattage bulb??? Any help appreciated
thanx
Brian

: I discovered that the little light bulb had burned out inside. It is a 3W 120V and "I'd like to know what it's for"

It's used as a nonlinear resistor in the feedback loop to stabilize the output level. They usually last forever since they don't glow (but I don't know about the Eico; I'm only familiar with H-P)

Such a temptation it is to comment that the waveshape matches the bulb shape. You MIGHT be able to retweak the feedback adjustment (I assume there is one) on the audio oscillator to improve the waveshape. The Christmas tree lamp has a lower resistance than the original and likely has upped the gain of the Wein bridge oscillator. You might try a 3S6 lamp. Like Alan, I'm not familiar with the EICO and I think hp used the 3S6 in the 200CD audio oscillator. If you can't find one, send me an e-mail. I have scads of them.

Dean

Thanx Dean I, appreciate that and I will try to find one first, and your right, it is a different shape and a different resistance. I cant believe I didn't think of that, although, I didn't realise that it was a feedback component as I've never seen a light bulb used in a circuit for anything other than an on/off swich.. This page Rules Thanx Brian

: Such a temptation it is to comment that the waveshape matches the bulb shape. You MIGHT be able to retweak the feedback adjustment (I assume there is one) on the audio oscillator to improve the waveshape. The Christmas tree lamp has a lower resistance than the original and likely has upped the gain of the Wein bridge oscillator. You might try a 3S6 lamp. Like Alan, I'm not familiar with the EICO and I think hp used the 3S6 in the 200CD audio oscillator. If you can't find one, send me an e-mail. I have scads of them.

: Dean

Brian,

Hold onto your socks! I've seen LEDs used for their 2v forward drop and they sit there glowing inside an instrument where no one can see them. It seems a little weird at first. One suspects that there's a tiny little technician inside that box that needs the light to work. It's an easy way to get a 2-volts reference rather than using 3 silicon diodes and zeners are harder to find below 2.4 volts.

Christmas break is beginning, so if you need the lamp before early January, contact me at home: dhhuster@semo.net

Dean