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Eico Model 315 SG
#1
Ok, started on this signal generator.. Got 2 of them.. One in good condition other missing a few things ..

Good one..

[Image: http://i292.photobucket.com/albums/mm38/...14yweu.jpg]

Missing a few things but chassis looks good inside..

[Image: http://i292.photobucket.com/albums/mm38/...cuq0mp.jpg]

Inside of 1st one looks like some parts replaced others original.. So I decided to power it up on Varaic..

No problem at 120 Volts draws about 300 Ma.

But No output..

More to follow as I have to take a picture of schematic to explain further..

Skip..
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#2
Like this??


Attached Files Image(s)
   
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow

Terry
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#3
YUP.. OK here is a picture of the input ( Grid) of the 6SL7 Pin 1)

[Image: http://i292.photobucket.com/albums/mm38/...2pi2vu.jpg]

Here is next picture measured at ( Cathode Pin 3 6SL7) NOTE: I also measured at C5 Same as before C5..

[Image: http://i292.photobucket.com/albums/mm38/...hquxny.jpg]

Same scale on both..

1ST Not a sine wave 2nd output should be much greater than input??? The 6SL7 tests good on tube tester)

Am I measuring at the right places?

Skip..

PS I will do a complete Recap But everything I measured so far looks OK..
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#4
Ok, Here is a little better schematic.. I hope...

[Image: http://i292.photobucket.com/albums/mm38/...sjhvr5.jpg]

Skip...
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#5
Just a couple of questions Skip, what are the plate voltages (or are those your notes on the schematic) and are there any paper caps in there?
John KK4ZLF
Lexington, KY
"illegitimis non carborundum"

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#6
Ok, The voltages on schematic are from this..

[Image: http://i292.photobucket.com/albums/mm38/...cykvhw.jpg]

I have not measured any myself yet..And Yes there are still paper caps present.

Here is a picture of bottom of unit.. Hard to get to some parts.. But not impossible..

[Image: http://i292.photobucket.com/albums/mm38/...cwleiw.jpg]

I guess I need to check all caps and replace Resistors as necessary..

I just wanted to see if it would work as is.. I guess NOT..

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#7
Is your 0D3 glowing inside (the tube not outdoors)??? Is the 10K resistor 10K?? In terms of amplitude the 6SL7 is being used as cathode follower to give a low impedance output. Wouldn't expect to see a lot of gain there. Amplitude is probably going to be about the same. The other half of the 6SN7 is the audio oscillator which generates the 400cy tone for the modulation.
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow

Terry
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#8
Terry, Yes the OD3 is glowing.. The 10K measures 10K well slightly less 9.8K

I am not getting same amplitude as input..Much less.. And its not a Sine wave like I think it should be..

Skip...
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#9
OK, I recapped all Capacitors.. I checked all Resistors and they were all within 10%..

So I hooked it up to my Spectrum ANA and saw a very nice signal.. around between -20 Dbm to -19 dbm max''

Someone had soldered close the part that houses the Attenuator resistors so I didn't check them out yet..

I checked out all bands and did a calibration .. All looks good now.. It doesn't put out a sine wave but the waveform isn't to bad looking..

I will check the attenuator resistors and do a cosmetic restoration.. OH and change out the connectors to BNC..then it should be good to go..

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#10
Well, I replaced the Atten Resistors and buttoned up the unit.. I did a final check at 5 frequencies across the bands and recorded the values.. when I hit band F it wouldn't start to oscillate until about 20 mhz. From 13 Mhz thru 20Mhz No signal output.. that also was the case on the harmonics it didnt start to work until 90 mhz..

1st question What would cause the loss of frequencies and 2nd how do I improve the accuracy..

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#11
1 Cln the bandswitch and or replace the osc tube.
2 Alignment
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow

Terry
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#12
Ok, Cleaned Bandswitch Again.. No Change

Replaced OSC tube with 3 more.. No change

Also Alignment Again.. Still Drops out at same Frequencies..

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#13
Is the F band adjustment the trimmer next the toggle sw?? If so give it a shot of deoxit spin it around a couple of times and let it dry out for while. Then give it a try. If that doesn't do it try compressing the coil just a little. Seems like your osc doesn't have enough feedback.
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow

Terry
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#14
Yes, Ok I will Try that...

Thanks
Skip..,
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#15
Ok, Tried all of that same problem..I even replaced the trimmer and coil from a parts set   same problem.. however I was able to get down to about 20 mhz before I lost signal..I tried to measure the grid of the OSC Tube pin 6  says it should be -.6 volts  I get -.04 volts..

When I go to other bands I get over -6 volts up to about -20 volts on band A..

PS Ready to give up on this.. All other bands work good...

Skip...
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