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 Post subject: Eico model 324 Signal Generator
PostPosted: Oct Sat 05, 2019 11:10 pm 
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Joined: Sep Sun 15, 2019 9:25 pm
Posts: 117
Location: Kingsport, Tn
This thing looks to be factory. I am ordering new paper caps from one of the dealers on the right. I did plug it up the other day after a quick check over just to make sure there was nothing serious wrong and it does more or less work. I hooked up its test lead and put it in close proximity with an am set I have and it picked up the signal on the appropriate frequency. The signal seemed very odd though and I’m hoping replacing the caps will fix some of that. I hooked up a small speaker to the audio output of the sig generator and it was so low I could hardly hear it. Does it need to be a speaker with external power? Also I’ve heard you can broadcast music to radios within about 50 ft of the set and I was wondering how to go about that. Is there a way to turn the signal tone off and play music through it? Thanks


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 12:10 am 
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Joined: Feb Wed 07, 2018 6:52 pm
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Location: Stone Mountain, GA
The audio signal out is not designed to drive a speaker.

You can feed audio in from a music source to the AF terminals and select EXT MOD on the SIGNAL SEL switch and it can be used as a transmitter.

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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 12:22 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 2178
Location: Dallas, TX
The modulation probably will not be up to broadcast quality. The circuit is very simple. Also the audio voltage amplitude needed is higher than most solid state sources.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 2:40 am 
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Joined: Nov Wed 08, 2017 11:52 pm
Posts: 290
Location: Phoenix AZ
I have one of this generators, it is fully restored with a built in frequency counter. The RF output signal is very distorted on most bands/frequencies and there is not much you can do to it to improve it. Also the modulated signal looks pretty bad. Regardless, it works OK for what it was original designed as a low cost general purpose signal generator.


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 3:46 am 
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Joined: Apr Fri 20, 2018 6:55 am
Posts: 106
Location: San Rafael, CA. 94903
Vinylnut91,
You can use it as a low power transmitter. input your AM signal into the external audio input and set the RF dial on the AM frequency you want to receive on. Add a length of wire to the output terminal for an antenna and, voila! Pretty rudimentary but it does work.
You also mentioned that the RF output looked rather insipid... That is inherent in this quality of device be it Eico, Paco and others. I have seen pictures in text books (1960's) showing what was expected to be seen from these RF generators. I have spent quite a few hours in the early days of my beginnings trying to improve upon the signal to no avail. There just isn't the circuitry there to support better fidelity. Also, it's not necessary for the results of the simple needs of an alignment. Frequency accuracy is more important, and that is a whole other subject...
Enjoy your new acquisition!
Best,
-marc


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 4:01 pm 
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Joined: Feb Sun 02, 2014 9:13 pm
Posts: 2152
Location: Roanoke, VA
Notimetolooz wrote:
The modulation probably will not be up to broadcast quality.

The modulation definitely will not be up to broadcast quality. The EICO 324 and other service/hobbyist grade AM signal generators generally use a directly modulated oscillator. That limits modulation to about 30% (as noted in the 324 manual) before envelope distortion and incidental frequency modulation begin to degrade the modulated waveform. Those generators were never designed for fidelity - they were designed only for alignment and basic testing.

I own a GR laboratory-grade generator that provides a modulation envelope with characteristics that meet the FCC requirements for AM broadcast stations. I need it on my bench for some of my work with small AM broadcast transmitters and for accurate measurement of the characteristics of communications receivers. I also use it for antique radio work. It is overkill for the latter, but there is no sense in having a second generator with lesser specs in the shop when I have and am used to using the GR. For those without my needs the EICO 324 and its kin are fine for antique radio service.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


Last edited by Dale H. Cook on Oct Sun 06, 2019 4:07 pm, edited 1 time in total.

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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 4:06 pm 
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upsss wrote:
The RF output signal is very distorted on most bands/frequencies and there is not much you can do to it to improve it.

You would not want to improve that, because reducing the RF harmonic content would degrade the generator's ability to work on multiple bands.

upsss wrote:
Also the modulated signal looks pretty bad. Regardless, it works OK for what it was original designed as a low cost general purpose signal generator.

Signal generators of this class were designed and built for a particular purpose in servicing, and do quite well at it.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Oct Sun 06, 2019 9:52 pm 
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The modulation input is 70k impedance and it needs 3 volts just to get to 30% per specs. So you will need a stepup transformer or such with a typical solid state source. I have a 324 and was thinking of trying it to broadcast to radios at home. But have not gotten around to it. The built in oscillator is not very clean so that does not mean the modulation circuit in the thing will be terrible with an external source, you have to try it. Look at this guy's info on that: https://people.ohio.edu/postr/bapix/Eico324.htm

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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Jan Sun 12, 2020 9:39 pm 
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Joined: Sep Sun 15, 2019 9:25 pm
Posts: 117
Location: Kingsport, Tn
Ok as for alignment. I own a few radios but I'm not at all CV confident in their alignment. I have an eico 425 oscilloscope but I don't think it will help me align it either, especially with no graticule. Any suggestions from the vintage electrophonatics? ;)


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Jan Sun 12, 2020 9:50 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 549
Location: St. Louis, MO
Vinylnut91 wrote:
Ok as for alignment. I own a few radios but I'm not at all CV confident in their alignment. I have an eico 425 oscilloscope but I don't think it will help me align it either, especially with no graticule. Any suggestions from the vintage electrophonatics? ;)


Do you have a frequency counter? That will let you adjust your SG's frequencies to be dead on, so you know that the signal you're receiving in your radio is dead on as well. You can get a cymometer off Ebay or Amazon for cheap. Power it with a wallwart.

Oh, you asked about turning off the modulation. On some SGs, you need to turn their switches to External Modulation, then just leave nothing plugged into the external jacks.

Make a graticule in Excel and print it to a transparency sheet. It worked for my Eico 470 and that was a big 7" scope. I posted the file here if you want to modify it: viewtopic.php?p=3066728#p3066728


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Jan Mon 13, 2020 3:06 am 
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Joined: Aug Sat 19, 2017 6:55 am
Posts: 179
Location: Glendale, AZ, USA
upsss wrote:
I have one of this generators, it is fully restored with a built in frequency counter. The RF output signal is very distorted on most bands/frequencies and there is not much you can do to it to improve it. Also the modulated signal looks pretty bad. Regardless, it works OK for what it was original designed as a low cost general purpose signal generator.


Just noticed this.
Would you mind telling/showing where you tied the frequency counter to in the circuit?
Thanks,
Russ

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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Mar Mon 30, 2020 2:31 am 
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Joined: Jan Tue 24, 2017 3:37 am
Posts: 18
Location: Ida, MI
I have been working on my Eico 324 for days now because the output waveform is so distorted.

The input to the output cathode follower (12AV7 pin 2) is a very nice sinewave, so
it's not an issue with the RF Oscillator. The RF is modulated via B+ on the cathode follower, so I checked that and there is some distortion there. As a troubleshooting isolation step, I replaced the .001 uF B+ cap
(C5) with a 100 uF. This eliminated anything coming into the cathode follower's plate, but it had little effect on the distortion. The top of the waveform is still smooth and symmetrical, but looks like it's pushed down some. The bottom is much worse. About half way down, it rounds out to flat clipping and then sharply joins the rising sinewave shape. I don't understand how a cathode follower can produce distortion like that. Any help would be welcome. : )

upsss: Your Model 324 upgrades look awesome. I may have to change mine over to BNC. PLEASE post some information on your addition of the frequency counter like where you got it and where you connected it. What is the BNC next to the RF Fine control hooked up to? Also, did you do anything with the output B+? I'm thinking it could use a better filter to remove everything over 400 Hz. Not to mention how low it is (54 V B+?) .


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Apr Mon 06, 2020 5:02 pm 
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Joined: Nov Wed 08, 2017 11:52 pm
Posts: 290
Location: Phoenix AZ
FuzzyDriver: You can see some more details of my frequency counter in this thread viewtopic.php?f=8&t=350360. There are too many threads on the Eico 324 to follow.

The BNC connector above the main output was my original RF output (before the attenuator) for an external frequency counter before I decided to install it inside the unit. Now I had an extra BNC at the output of the generator and the input of the counter. So, if I disable the oscillator of the SG I can use the frequency counter to measure any external signals.


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Apr Tue 07, 2020 9:53 pm 
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Location: Ida, MI
Thanks upsss! The info you put in that thread pretty much covers everything. I needed my 324 to do an alignment on a Zenith AM/FM 7T04, so I already put it back together with the new upper BNC connected to the cathode of the cathode follower (rather than between the 68 ohm resistor and pot). My Heathkit IM-2410 likes it just fine and I'll just use that for setting the 324 output freq, at least for now. I spent way too much time updating that 324. I built it a new power supply using a silicon rectifier, bigger filter caps, and a slightly smaller dropping resistor. RF B+ ended up rising only 5 V. I also replaced that old, cracked original power cord with a new 3 prong cord and eliminated the two caps from incoming power to chassis. I think that's an important safety upgrade. The only original caps in it now are the two in the RF signal path (C6 and C7).


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Apr Wed 08, 2020 6:44 am 
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Location: Phoenix AZ
Make sure you put a series capacitor ~1000pf going to your counter BNC connector. Also, You should replace the C1, C2 capacitors with "Y" type capacitors and NOT eliminate them!


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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Apr Wed 08, 2020 8:10 am 
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Location: Annapolis, MD
The output waveform is supposed to be distorted---that how they get the highest frequencies (harmonics). I advise avoiding the temptation to fix this non-problem.....

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 Post subject: Re: Eico model 324 Signal Generator
PostPosted: Apr Sun 12, 2020 5:23 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1088
Location: Canton,Ohio.United States
Hey Guys
I know one neat thing I use mine for sometimes, and no mod is required.
Dxing single side band transmission. I tune in to hear the mushy audio, then turn the frequency of the 324 to match. Just lay the RF cable by the radio. It drifts some, so you either get donald duck or Alvin and the chipmunks. But it makes the transmission understandable.

John


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