andre tchmil

signal generator problem
« on: August 02, 2016, 12:36:50 PM »
I have a Levell PC200 signal generator here.
Works fine , except when I change the multiplier switch , it takes a while till it kicks in.
I don't have any schematic,
elco's measure ok but it sounds like something needs to get charged before it works.
Any idea where to start ? :)


abbey road d enfer

Re: signal generator problem
« Reply #1 on: August 02, 2016, 01:22:58 PM »
I have a Levell PC200 signal generator here.
Works fine , except when I change the multiplier switch , it takes a while till it kicks in.
I don't have any schematic,
elco's measure ok but it sounds like something needs to get charged before it works.
Any idea where to start ? :)
Brings back very old memories. IIRC, it's a sine wave oscillator with either a bulb or a CTN in the negative feedback loop. Settling time is a compromise with low THD. In  that type of oscillator, there is generally a trimmer that governs this compromise, so I suggest you try the trace some of the schemo and look for a trimmer. If you move it in one direction, it won't start oscillating, move it in the other direction, it will kick in quickly, but with increased THD.
Now, my memories can be awfully wrong; if it's the case, just forget it and vow me to hell.  :o
PS: sometimes, there is no trimmer, and as time goes by components drift; then you have to adjust one of the resistors in the NFB loop.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

andre tchmil

Re: signal generator problem
« Reply #2 on: August 02, 2016, 01:51:36 PM »
I have a Levell PC200 signal generator here.
Works fine , except when I change the multiplier switch , it takes a while till it kicks in.
I don't have any schematic,
elco's measure ok but it sounds like something needs to get charged before it works.
Any idea where to start ? :)
Brings back very old memories. IIRC, it's a sine wave oscillator with either a bulb or a CTN in the negative feedback loop. Settling time is a compromise with low THD. In  that type of oscillator, there is generally a trimmer that governs this compromise, so I suggest you try the trace some of the schemo and look for a trimmer. If you move it in one direction, it won't start oscillating, move it in the other direction, it will kick in quickly, but with increased THD.
Now, my memories can be awfully wrong; if it's the case, just forget it and vow me to hell.  :o
PS: sometimes, there is no trimmer, and as time goes by components drift; then you have to adjust one of the resistors in the NFB loop.

There's a bulb in it yes.  8)
But i'm afraid I wont be able to get a schemo

Walrus

Re: signal generator problem
« Reply #3 on: August 02, 2016, 01:59:42 PM »
Never heard of a PC200, but have seen TG200......
Kevin.

andre tchmil

Re: signal generator problem
« Reply #4 on: August 02, 2016, 02:01:38 PM »
Never heard of a PC200, but have seen TG200......

Damn, I didn't look at the frontpanel, stupid me.

it is a TG200 ;D
pcb is PC200
found a schematic as well.
thanks for waking me up guys  :P
« Last Edit: August 02, 2016, 02:09:44 PM by andre tchmil »

arnyk

Re: signal generator problem
« Reply #5 on: September 15, 2016, 12:58:29 PM »
I have a Levell PC200 signal generator here.
Works fine , except when I change the multiplier switch , it takes a while till it kicks in.
I don't have any schematic,
elco's measure ok but it sounds like something needs to get charged before it works.
Any idea where to start ? :)

That is how it works for any analog audio generator. The design is always a trade off between operating frequency,  distortion, and settling time.   Some do it better, some do it worse, but they are all based on the same laws of physics.

I can't even find any reference to the Levell PC200 with Google, so I'm guessing that it was built back in the days when dinosaurs roamed the earth. ;-)

A newer, better generator can no doubt be found on the used equipment market, complete with documentation.

However, your basic problem is that it is an analog dinosaur in the digital age.  A wave table, a DAC, and a buffer plays by a more useful set of rules and does not have the same limitations.

If you use Audacity freeware to generate the sine wave and play it through your computer's audio inteface, you'll probably obtain better performance in most if not all areas with an out-of-pocket expense of the ever-popular, totally  free.