refurbishing a Wavetek 111 signal generator

[marc brown]

I'm entering a new realm here of rebuilding/repairing old audio equipment. To that end, I picked up a Goldstar 9020 oscilloscope and a Wavetek 111 signal generator.

Before diving into my Kenwood KA-7100, I was testing the output from the Wavetek using the scope and while the Wavetek does produce what you could call waveforms, only the sinewave could be adjusted to produce what you would call a clean waveform.

Do I need to clean/adjust my Wavetek or is it too crude to produce decent waveforms?

 

[gmphadte]

My wavetek 188 has at least half as many presets as the resistors. That means most of the circuits need to be calibrated/adjusted using these presets according to the procedure (if)supplied with the service manual.

See if you can find a service manual on the net and then decide.

Gajanan Phadte

 

[macboy]

A nice sine is much harder to produce than a decent looking square or triangle.
Get your hands on the service manual, which is easy to find with google's help.

 

[marc brown]

Thanks guys. I've got the instruction manual and tried last weekend to calibrate my Wavetek. Starting off, you are supposed to adjust two potentiometers to set the main power supply voltage. You are supposed to read + and - 6 volts at the power supply caps. I only got 1.5 volts and the potentiometers didn't seem to do anything. Also, the attenuator on my generator is bad.

 

[macboy]

This is an old piece of gear. There are a lot of things to go wrong. I would first suspect dried up capacitors. Measure the voltage across C1 and C2 in the power supply (2000 microF 15 V caps). According to the manual, they should have about 14 V each. This should be relatively clean DC. If you new(old) 'scope works, have a look at the voltage. You can also measure the ripple with a good multimeter set on AC Volts. A little ripple, up to a volt or so peak-to-peak, would be OK, but anything more than that could mean bad capacitors. If the voltage here is OK, then there is something else wrong in the regulators. I'd be tempted to rip the old discrete regulators out and just use LM7806/7906 or LM317/337 regulators in their place, instead of trying to troubleshoot and fix the original circuit.