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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: 265
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?
Attachment:
eico_368.jpg
eico_368.jpg [ 83.87 KiB | Viewed 727 times ]


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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: 988
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: 265
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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Joined: May Wed 18, 2011 2:40 am
Posts: 2913
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: 265
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: 265
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.
Attachment:
eico_368_2.jpg
eico_368_2.jpg [ 15.85 KiB | Viewed 616 times ]


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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: 10536
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
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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: 265
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: 8651
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: 265
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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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Fri 24, 2017 7:37 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 265
I decided to try this on a known good and aligned radio (aligned using my scope and Triplett 3434A). When I attach it to the grid (pin 1) of the IF Amp 12BA6, and attach the scope per the Riders instructions (to pin 1 grid of the 3rd FM IF amp 12AU6), I am not getting a nice peak waveform. Using the same points and the Triplett, I can get a nice peak with the marker freq visible. I tuned the sweep osc freq through where 10.7MC would be on the dial, and when I hit what I think is that freq, I get this waveform.. I am using a 10.7MC crystal for the marker, same as how I used the Triplett... Would anyone have any suggestions on where to start, as I assume something is not working correctly with the EICO...
Attachment:
EICO_368.jpg
EICO_368.jpg [ 241.36 KiB | Viewed 422 times ]


Here are the settings on the EICO:
Attachment:
EICO_368_2.jpg
EICO_368_2.jpg [ 216.44 KiB | Viewed 417 times ]


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Sat 25, 2017 12:20 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 8651
Location: Powell River BC Canada
Are you using the X-Y mode on your scope on page 4-6 of the Tek manual ?

The thing to remember, with the Eico 368, is the signal at the Hor. output is
60 Hz, as is the output, through the demodulation probe connected to scope
vertical.

Check page 7 in the Eico 368 manual. The scope traces should be single
lines. If there is any garbage from the 368 Hor. terminals check C26 and
make sure the ground binding post is connected properly.

Why is the RF output level set to maximum ? Can you post
the Rider setup for the receiver you are aligning ?


I own a 368 and have used it with modern scopes on X-Y mode.

_________________
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 Sat 25, 2017 5:34 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 265
I am using the X-Y mode of the scope the same as I did with the Triplett 3434A. The radio I am doing is an RCA 2-XF-91, I found the schematic on Nostalgia air. I checked the horizontal output of the generator and see a clean 60 hz sine wave. I replaced C26, rechecked it and it measures .06 uF. I also checked resistors R38/39/40 and they are ok.
I am currently doing the step where I would adjust the T5 top core. I have the scope connected through 220K ohm resistor to pin 1 of V5, and the signal is going into pin 1 of V4... I basically had everything hooked up using the Triplett, had a nice single line curve with the marker visible right at the peak. I then swapped out the Triplett for the EICO, and can not get the proper single line curve. I tried lower settings of the RF output but could only see anything on the highest coarse setting as the picture shows. It does seem like an issue with the horizontal sync, but I am not sure.
Here is what I get with the Triplett:
Attachment:
CameraZOOM-20170225112430753.jpg
CameraZOOM-20170225112430753.jpg [ 175.18 KiB | Viewed 379 times ]


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Sat 25, 2017 9:44 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 8651
Location: Powell River BC Canada
Your scope is displaying the swept IF frequency found at the grid of the limiter tube.

Could you show a screen shot of your scope settings .

That point is not an easy pick off. The VTVM in the RCA procedure has an
impedance of 11 megohms. The VTVM sees only DC, even though its loaded with
RF. You might try a 68 K resistor in series with the scope probe, with a 0.01 uFd
between ground and the end of the resistor that goes to the V input.

Check the values of R5,6,7,8,9,10,12. These can easily be blown open
by past use accidents.

Also back off the RF output level, start at the lowest and work up.

The scope needs to see the DC component of the swept signal detected and
displayed as a varying DC signal at 60 Hz. Your 2235 scope is showing raw RF.

Below is what Eico has on page 5 of the manual. Read the entire manual.

There is no sync issue in the Eico 368, only phasing.

Attachment:
EICO 368 MANUAL   SEGMENT..jpg
EICO 368 MANUAL SEGMENT..jpg [ 160.53 KiB | Viewed 368 times ]

_________________
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 Sat 25, 2017 11:37 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 265
I checked those resistors, OK. I also did all the resistance checks in the chart in the manual, all OK.
I tried the 68K resistor and also a .01Uf to gnd as you suggested, no real help.. Here are the scope and EICO settings as well as the latest scope trace:
Attachment:
scope_settings.jpg
scope_settings.jpg [ 237.9 KiB | Viewed 358 times ]

Attachment:
latest_eico.jpg
latest_eico.jpg [ 215.86 KiB | Viewed 358 times ]

Attachment:
latest_pic.jpg
latest_pic.jpg [ 252.29 KiB | Viewed 358 times ]


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 Post subject: Re: Recapping Eico 368, cap seems to be missing
PostPosted: Feb Sun 26, 2017 12:44 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 265
D'oh... I decided to recheck all my recapping activity, and I discovered that I had the negative side of C22 connected to the wrong side of the AC line.. Instead of having it connected to L8, I had it tied to L7.. After correcting that it works much better now. Thanks for taking the time to help me, hopefully this will be a learning lesson for the next time... Here is what I get now:
Attachment:
eico_fixed.jpg
eico_fixed.jpg [ 188.98 KiB | Viewed 351 times ]


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