Which cap to replace first...

[eccerr0r]

Was testing this Eico 320 and noticed though it mostly worked, it seemed to behave weirdly. The amplitude showing up on my scope is really unpredictable - as I change the frequency, amplitude changes...

As my scope is only around 20MHz and this signal generator is 150KHz-34MHz, and 17MHz to 102MHz in harmonics, I expect there probably is some weirdness...

The signal generator clearly works as it easily swamps out a radio reception if it's nearby. FM stations get swamped out to silence when a harmonic is set...

... so most of the caps actually work. And I don't hear any hum...

So which to replace first if any?

[Sparkey55]

Re: Which cap to replace first...

Was testing this Eico 320 and noticed though it mostly worked, it seemed to behave weirdly. The amplitude showing up on my scope is really unpredictable - as I change the frequency, amplitude changes...

As my scope is only around 20MHz and this signal generator is 150KHz-34MHz, and 17MHz to 102MHz in harmonics, I expect there probably is some weirdness...

The signal generator clearly works as it easily swamps out a radio reception if it's nearby. FM stations get swamped out to silence when a harmonic is set...

... so most of the caps actually work. And I don't hear any hum...

So which to replace first if any?

ALL the electrolytic caps starting with the main power supply and ALL the paper caps and any waxed oil filled caps and maybe any old micas.

[R_J]

Re: Which cap to replace first...

I would first clean the controls and the switches with a control cleaner/deoxidizer

[goontron]

Re: Which cap to replace first...

Always the filter! Those shrapnel generators are not to be messed with!
I don't see any bumblebombs, otherwise those would need to go yesterday!

[eccerr0r]

Re: Which cap to replace first...

The frequency control is based off a variable capacitor and that control, cleaning doesn't really do much since there's no touching contacts!

I guess I meant this as a somewhat sarcastic post as most of the caps in this signal generator, according to most sites on the web, are target for replacement... but I'm very surprised it even works and other than transformer buzzing, I don't seem to see 60 cycle hum on the output.

Kind of strange that Eico switched over from the 2-tube 320 to the 2-tube 324, but the 324 uses a semiconductor rectifier. The (newer) 324 I have uses a silicon diode instead of the rectifier tube in the 320.

[stj]

Re: Which cap to replace first...

anything that old, replace the power cord too, or the insulation may crack.

[R_J]

Re: Which cap to replace first...

The frequency control is based off a variable capacitor and that control, cleaning doesn't really do much since there's no touching contacts!

The switch I was referring to to clean was the Band switch, not the open air capacitor. The switch switches in the different coils for different frequencies, if its dirty, the freq. could shift

[eccerr0r]

Re: Which cap to replace first...

I guess that main selector switch I did clean out, but it wasn't the frequency that was the issue - the frequency was fairly stable. The amplitude was what is strange, almost seems there's a multiple pole filter on the output of the LC oscillator which honestly I can't blame bad capacitors... well, maybe, but don't know.

It may well be simply due to the design of the oscillator as it's a very cheap design (one tube used for both AF/modulation and the RF oscillator).

[Agent24]

Re: Which cap to replace first...

So which to replace first if any?

I'm no expert in valve stuff, but from what I know, I'd say all or most of them, even if they work now, they can well go shorted later. Explosions or cooked transformer is not desirable.

Also check the resistors, those old carbon-composition resistors (very different to carbon-film) often go open or significantly change (increase) in resistance and throw the circuit out of whack.

[R_J]

Re: Which cap to replace first...

Get a plastic stick and poke and move things around a bit, it might show an intermitint component, I would move the tube around in the socket as the tube pins and the socket could be tarnished, lightly taping the tube could reveal an intermitint short in the tube. other than that. looking at the diagram, there's not much that could go wrong.