EICO 324 - capacitors in original probes?

9/26/2011 3:09:07 PMBrian

My sig gen came from eBay without the probes. Are capacitors C4 (RF?) and C9 (audio) meant to isolate DC from the probes? There were no capacitors in the original probes for RF or audio outputs?

9/26/2011 4:50:57 PMEdd

Sir Brian. . . . .

You are exactly CORRECT on those suppositions.

73's de Edd

I had to stop driving my car for a while... The tires got dizzy..

:My sig gen came from eBay without the probes. Are capacitors C4 (RF?) and C9 (audio) meant to isolate DC from the probes? There were no capacitors in the original probes for RF or audio outputs?
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9/26/2011 4:57:09 PMDoug Criner

Yes, that's reason for the two coupling caps. I moved my two caps to inside the cabinet, right at the connectors - I don't know why EICO put them inside the probes. Check to see if a prior owner did the same mod to your 324. That way, you can use garden-variety probes.

I also changed the RF-out connector to BNC - so it fits modern probes. A BNC connector will fit right into the mounting hole used for the original, obsolete mic connector.

9/26/2011 5:21:10 PMDoug Criner

Addendum: According to my original schematic, both C4 and C9 were located inside the chassis, not in the probes.

Regarding the audio-in connectors: those are the old banana-style jacks. I didn't worry about modernizing those - I never use them, only the built-in 400-Hz audio modulation feature. The audio-in connectors would be useful if you wanted to turn the 324 into a minature AM broadcast station using, for example, an FM tuner or other line-level audio source. I haven't tried that, but the built-in 400-Hz tone can be picked up on radios throughout my house.

9/26/2011 10:53:05 PMBrian

Do you connect a wire from the radio chassis to the ground pin shown on the sig gen, for both RF out and audio out?

:Addendum: According to my original schematic, both C4 and C9 were located inside the chassis, not in the probes.
:
:Regarding the audio-in connectors: those are the old banana-style jacks. I didn't worry about modernizing those - I never use them, only the built-in 400-Hz audio modulation feature. The audio-in connectors would be useful if you wanted to turn the 324 into a minature AM broadcast station using, for example, an FM tuner or other line-level audio source. I haven't tried that, but the built-in 400-Hz tone can be picked up on radios throughout my house.
:

9/26/2011 11:22:20 PMEdd

Sir Brain . . . . .

The aduio connector is a given with it consisting of two bannana or 5 way binding posts spaced apart . . . possibly being the the same spacing as a GR plug.

The RF connector appears to be using an Amphenol connector, in which case the ground is being made by the mounting of the units outer threaded shell.

Usually one breaks out of the outer SHIELD at the far end of the probe and has a sho0rt 6 in or so length of hook up wire connected to an alligator clip. That then makes your ground at that end to the tested equipments chassis.

The Amphenol mating connector:

73's de Edd

Seen it all . . .Done it all . . but can't remember most of it.

:Do you connect a wire from the radio chassis to the ground pin shown on the sig gen, for both RF out and audio out?
:
:

::Addendum: According to my original schematic, both C4 and C9 were located inside the chassis, not in the probes.
::
::Regarding the audio-in connectors: those are the old banana-style jacks. I didn't worry about modernizing those - I never use them, only the built-in 400-Hz audio modulation feature. The audio-in connectors would be useful if you wanted to turn the 324 into a minature AM broadcast station using, for example, an FM tuner or other line-level audio source. I haven't tried that, but the built-in 400-Hz tone can be picked up on radios throughout my house.
::
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