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 Post subject: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Wed 01, 2017 10:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 245
Just got an Eico 368 sweep generator, I found all the paper and e-caps to replace except one, marked as C20 (.22 uf 200V) in this excerpt, it is not there. Not sure how critical this is, or if this would have worked without it? I do see that C21 has been replaced with a newer e-cap, and it attaches to one side of that black encapsulated transformer thing they call an 'increductor', and one side of C20 would also attach there... Also, the schematic I have has marks on it from an assembler, and all the parts in the parts list have check marks next to them except C20, which has a line through it.. maybe this part was eliminated intentionally?
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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Thu 02, 2017 12:42 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 957
Location: Tucson AZ
I have one of these also. I just opened it up and did not find C20 either.

Not sure why.


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Thu 02, 2017 3:21 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 245
Thanks for checking, I guess I will not worry about it... Had to order some of the caps, hopefully it will work once I am done...


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Thu 02, 2017 6:30 pm 
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Location: Littleton, MA
The Eico 368 manual on BAMA says: "Capacitor C20, which is in parallel with the inductor primary, has been chosen to resonate with the inductor at 60 cycles in order to increase the available range of control current and therefore the available range of sweep width."

So I suppose that if the width of the sweep in frequency is adequate for your purposes, you don't need C20. But if the frequency span isn't high enough, you'll know why.

I see that in a previous thread on the Eico 368, John Kusching also noted that C20 was missing in his 368:
viewtopic.php?t=66463

The BAMA manual for the Eico 369 sweep generator also shows a resonating capacitor on the increductor primary. The circuit description contains the same text as in the Eico 368 manual. In the Eico 369 schematic, it is C25.

Perhaps C20 was a later addition, and earlier versions of the 368 don't have it?

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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Thu 02, 2017 6:52 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 245
My sweep width will be for FM alignment purposes, I guess 400-600 Khz depending on the instructions.. I have that size cap, maybe I will try with and without to see if there is any difference, once I get it working...


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Wed 15, 2017 11:10 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 245
Another question on this one... I am looking at replacing the caps where the AC line comes in, there is a network of caps and coils. The caps are 3-legged ones, and they are marked with .005, but the parts list shows them (C28 A/B and C29 A/B) as .05 uF, not .005 uF. Given the small size (about a half inch diameter) I am assuming they are .005 uF? I have both .0047 and .047 uF Y2 safety caps, so I can use either.
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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Thu 16, 2017 12:29 am 
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Posts: 10140
Location: S. Dartmouth MA 02748-1225 USA
Use the .0047. If the larger value is used there will be too much pass through AC current, (.1 mf) and a spark or noticeable tickle will occur. The caps also resonate with the inductor for effective RF filtering. If it is possible, check the MF value of the existing caps.

IMHO add the resonating capacitor. It is better to have the excess sweep. If the sweep is used close to the extreme end it is likely to be non-linear and give a strange trace. Use a good metal foil/poly cap in that location not a metalized.

YMMV

Chas

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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Thu 16, 2017 12:38 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 8397
Location: Powell River BC Canada
Another issue. There have been 240 volt versions of this unit. Remember,
the sweep functions are directly connected to the power line, and not to
a secondary winding of the power transformer. Some transformer replacements
to 240 volt conversions may have overlooked this. Which is a doom move.

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Fri 17, 2017 4:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 245
Finished recapping this, trying it out. With a scope on the output, and no marker or sweep setting, I do see a decent looking sine wave which does vary as I change the sweep frequency range control.. However I am not sure how accurate this is.. With my scope at .1 microsec per division, and the dial set to 3.0 Mhz, a full cycle of the wave is about 21.5 divisions on the scope. My math comes up with 4.6Mhz for this. Tried also with the dial at 4.0 Mhz, and I come up with 11 divisions for a full cycle, which is about 6.25 Mhz.. I have ordered a diode to build the Broadband detector circuit which I will try out... but in the meantime could this thing be that far out of adjustment?


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Fri 17, 2017 6:58 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 8397
Location: Powell River BC Canada
Can you connect the 368 to a Variac, and see how the output frequency
shifts with line voltages from 110 to 125 ?

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Fri 17, 2017 7:26 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 245
Sorry, don't have one of those... I ordered one, have been meaning to get one anyhow.. Once I get that along with the diode, I will build the broadband detector and delve deeper into this, in a week or so.. I will update then, thanks for the suggestion...


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