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 Post subject: Eico 324 find
PostPosted: Feb Sun 02, 2020 12:46 am 
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Location: Boise, Idaho
I was not looking for a signal generator but the opportunity presented itself so I picked it up. It has been sitting in the basement of an electronics store I go to. They used to service radios and all other types of equipment. Figure it has been sitting there since the 70’s or 80’s. Now I have a number of questions.

1) I read somewhere that if the equipment was built by Eico the tube sockets and other ancillary connections were riveted, not bolted to the chassis. Is this true? Everything is riveted inside this one and it also has the sticker on the back.

2) Are the turquoise colored capacitors really paper? That is what the parts list calls them out as but I have not seen paper caps that look like that before. They look more like Mica.

3) The parts list calls for a 12AU7 and 12AV7 tube. This has two 12AU7 tubes. ???

I don’t know how good of a signal generator these were, it certainly is not in the same league as my GR 1001-A, but at least I have spare now it will look nice sitting next the my other Eico test gear.

Thanks in advance for any input.


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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 1:04 am 
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Location: Ohio 45177
Yea even the transformer is riveted in. And I don't see a selenium rectifier? That may be a late production factory build. Thus the caps may be of a better type. It is still listed in my 1970 Allied catalog. That seems late. It was 44$ factory wired. Mine had wax paper caps in it that I replaced. I wonder when they quit making the 324, then. Those blue caps look too small to be paper of any sort, to me. I suspect they may be mylar or something. I would be tempted to leave them alone, but then I have a tester for leakage so I could resolve any doubts. The 12AV7 oscillator might have been a production change too? If you do change it to the AV, I would expect to have to recalibrate it. Well test it and see how well it works. Might just be a case of leave it alone.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 2:22 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
You are correct, sir. No selenium rectifier.

I have the 20/150 caps replaced and also removed the old Switchcraft connector and replaced it with a BNC. I am pretty sure I have those value caps in stock...the ubiquitous yellow ones. As long as they are not paper my guess is they are still ok.

He also had a 950B in the same drawer but I passed on it since I already have one. Heck, I may go back next weekend and open it up and see. If its a factory build I may just buy it for the heck of it.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 3:30 am 
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Location: Fernandina Beach, FL
Check it out, but are the turquoise capacitors Mylar?

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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 4:27 am 
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Eico factory built will have the letter W in the serial number-either at beginning or end (I forget which).
Rick


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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 3:41 pm 
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Location: Boise, Idaho
I do not see any stamped serial number on it, only the sticker on the back as shown in the photo. The smaller sticker on the top is has the numbers 0161 on it. January of 1961? Maybe.

I brought it up last night, fairly fast, on the ole VTransformer. Band B has output issues. My freq. counter stopped reading a signal throughout the entire range. All other bands seem to work but calibration changes throughout the spread. In other words, at 3.5 mc on the dial, the freq. meter reads 3.5 and some change. But at 11.mc on the dial the freq. meter reads 10.7.

I think step one is to check the band switch, then check resistors, then those turquoise caps and of course determine if there was an accidental tube change. Both look to have the same age on them, same brand even. I am slapping myself for not asking for the original manual, but I will make that call. The manual from BAMA, like so many others is poor quality.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 6:57 pm 
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Location: Long Island NY
In the late 1960s and early '70s Eico was getting away from kits and more into factory assembled test equipment. Some of it was really good on a service shop level. This particular signal generator was probably in that league; had it been built for the vocational school or educational market it would have had a three wire cord on it.

For their size and apparent age, it's a safe bet the small caps are Mylar and probably don't need to be changed. The dual section Temple filter cap, on the other hand, is probably due for replacement at this point. One could test it after running it a while to let it reform but most of them don't bounce back at this point. If the cap is failing the B+ voltage will be low and the generator might not work so well on some bands. Usually the higher bands get erratic or stop working first when there is a problem.

The 12AU7 and 12AV7 are close cousins, so the swap probably worked okay. However. the 12AV7 was specifically designed for VHF service as an oscillator, mixer, and amplifier, and it is used as the RF oscillator and buffer in the Eico. It has higher gain and considerably less output capacitance. The signal generator will probably have more RF output, particularly at high frequencies, with a 12AV7 in it.

As for frequency calibration, Eico stated the dial accuracy as +/- 1.5% so as long as you are within that range it's OK. 10.7 at 11 MHz is 2.7% so that is a bit off but not terrible. It should be possible to bump it in a little closer. If you can get the original manual that came with the generator it would be a good thing. The 324 was in production for about 15 years and there were changes along the way. The manuals online may be from earlier versions of your generator so they'll be close but some details will differ.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 02, 2020 9:16 pm 
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Location: Boise, Idaho
Thank's Chris. Would the swap to an AU have required any other changes? I personally like to have things as close to OEM as possible so I will need to buy an AV7.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 03, 2020 2:55 am 
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Radiolaguy has a 324 on his site that looks like yours inside. Same small caps and riveted together. The one feature I see is that it has a stamping on the top of the chassis that is a signed factory acceptance for testing and the date looks like 197-something. It also appears to have Eico branded tubes installed. I still believe that going from AU to AV will possibly result in a change in calibration due to the tube internal capacitance and differences. Maybe not much? Maybe it was a fudge-it substitution to begin with, who knows.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 03, 2020 3:05 am 
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Location: Long Island NY
Quote:
Thank's Chris. Would the swap to an AU have required any other changes? I personally like to have things as close to OEM as possible so I will need to buy an AV7.


It should not have required any wiring changes to the generator. The two tubes have the same pin-out. I don't know if you'll see a dramatic real night-and-day difference at AM broadcast band and IF frequencies, but it could make a difference on FM and VHF. Thing is, if you are going to calibrate the generator it would be good to get it into the best shape possible (with the correct tubes) first. It is possible the difference in calibration you are seeing between 10.7 MHz and 11 MHz is due to having a 12AU7 in the oscillator section.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 03, 2020 3:44 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
All the Eico factory built stuff (school sets) here have those labels
inside. The glue might have let go long ago.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Sun 09, 2020 4:58 am 
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The serial number on those is usually engraved on the front panel in the top left corner.
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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 10, 2020 1:36 am 
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Location: Boise, Idaho
I received NOS 12AV7 and put it in. Ehhh, still not impressed with this. I did find a broke coil wire on band B coil, which was why that would not work. Soldering those tiny wires is always fun...not, but is done and band B is alive again.

Calibration on this is not that great on any band. A few are ok at the upper and lower sections but most of them are off by a few marks. IOW, to get 600KC it needs to be at 555-560 on the dial. This seems to be consistent behavior on all the bands except the 3.5-11kc band where is almost dead on.

Any reason I can't simply use a frequency counter for calibration instead of a radio (and radio stations) as described in the manual?

Also, attached are a comparison between my General Radio signal generator and the Eico, both at 600kc. The Eico has the ugly tail on the bottom on all bands except band E and F. (11-145 mc). I would not expect it be as nice of a sine wave as the General Radio, but still...is that normal for these?


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GR.JPG
GR.JPG [ 170.65 KiB | Viewed 697 times ]

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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 10, 2020 2:18 am 
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Yes it's normal. As a corollary they create the harmonic bands. If you want precise frequency, the E-200C does very well. And of course you can use a counter if you can get a place with enough signal. Some have modified to supply a counter signal before the output attenuator, thereby worsening the already poor ability of the generator to supply tiny signals.


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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 10, 2020 3:39 am 
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Location: Boise, Idaho
bob91343 wrote:
Yes it's normal. As a corollary they create the harmonic bands. If you want precise frequency, the E-200C does very well. And of course you can use a counter if you can get a place with enough signal. Some have modified to supply a counter signal before the output attenuator, thereby worsening the already poor ability of the generator to supply tiny signals.


Thanks. So are you talking about the Precision E-200C?

I keep looking for a BK E200D to go with my E310B but I have yet to find the right deal. I like my General Radio 1001A but the older I get the less I like moving it. It's a beast. I really want something lighter which is why I thought I would try the Eico.

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 Post subject: Re: Eico 324 find
PostPosted: Feb Mon 10, 2020 4:48 am 
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Yes, Precision. I disliked that generator from the get go. Its frequency accuracy is, for me, its only asset, besides being not too heavy.

I dislike the incidental FM and the unknown output signal amplitude. But for what it is, I guess it's okay. I am spoiled by my HP 8657B. Better stability and accuracy than anything else I have used. And its minimum signal is really small.


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 Post subject: Re: Eico 324 find
PostPosted: Apr Thu 02, 2020 10:13 am 
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Location: Ida, MI
My Eico 324 output looks a lot like yours, maybe a little better. Did you check the input signal to the cathode follower (V2, pin 2)? When I check the signal there it is an almost perfect sine wave, which makes me think the distortion is due to the way the cathode follower is set up. What are you getting for B+ with the silicon rectifier?

Also, I spent a good many hours redoing almost all of the 324 schematic and uploaded it to my site. Grab a copy here:
re-worked EICO Model 324 Schematic if your schematic is as bad as mine was.


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