I need a schematic for this Eico 315. It’s not normal because it has Ceramic coils, and no I haven’t been drink yet. It has (6) Six individual coils and (6) Six individual Trimmers all made of ceramics. Has anybody seen one of these Signal Generators yet. How do you add Attachments?

Send your email if you need higher resolution.
-Chuck

Instruction manual construction manual and schematic.
http://bama.edebris.com/manuals/eico/315/

Dave

The Eico 315 was pretty popular in its day. It went through a number of production changes during its life; you'll find some with 7F7 loktal tubes in place of the 6SL7, ceramic coil forms vs. paper, and so on. The big, well marked tuning dial is surprisingly well calibrated, the band switch shorts out the unused coils to prevent unwanted resonances, and it even has a vernier dial with reduction drive. It will do nearly everything you'd ever need or want for fixing antique radios.

I'm new at posting so bare with me. I purchased this eico 315 about 2 weeks ago on Ebay as is, and to my suprise it was really clean inside almost new, but it had ceramic coils inside not cardboard. I have schematic of the standard eico 315. maybe Eico made a mod and didn't update the schematic are something. i'm trying to send attachments so you can see what i'm talking about, they say a picture is worth a thousand words... Well i'm trying to get you that picture.

I wouldn’t complain too much. By the time this generator was designed they had a number of ultra low loss, temperature and humidity stable ceramics for coil forms. All the best signal generators of tge day used ceramic forms too. The cardboard coil tubes in other versions of the 315 were likely a downgrade made to lower cost.

As with a lot of vintage electronic products, the manual that came with it is the manual to rely on. Almost nothing made back then stayed exactly the same from the very first unit off the production line to the very last. The manuals you find online may be for different years, versions, or production runs so you have to accept that there will be some variations here and there.

I'm back with a thousand words

Thanks for the advice Chris, I have noticed some things about this unit. By going through and going over every part, they used a lot of mica's. and the tubes tested strong like new. The problem might be the audio choke, it looks like somebody replaced it because it's loose and held by one screw.

wowzzers, that is one clean unit inside. Quite the contract with the outside. I think It deserves a full restoration. Tread lightly in there, although there are probably few unobtanium parts.

Looks like the front panel could benefit from a nice cleaning with dilute ammonia solution, or perhaps not so dilute. Just follow up with water. The meter bezel could be repainted. After thorough cleaning, I think you'd have a "like new" unit there

Everthing about this is strange. it's like brand new with the exception of the Audio Choke. it has temperature control capacitor and only (3) paper capacitors. I started to clean the face a little, and the restore is going to be slow.

For What It's Worth, I just checked the famous auction site for the 315. Most were in the same or worse cosmetic condition. I thought if they looked nice and went cheap, you wouldn't have to spiff up the outside. Guess not...

If the mounting holes match, I wouldn't jump to the conclusion that the choke has been replaced. It's a kit, one of the mounting screws might have been lost during construction, or been insufficiently tightened and worked its way loose over the years.

The ceramic trim capacitors are the same as on my 315, except for band F:



Your 315 should have six or seven paper capacitors, depending on whether you can find C11 or not (I don't see it on the schematic nor in the construction manual). I counted at least five in your photos. Just because they have a shiny cylindrical plastic case or a molded rectangular case like a large old-style mica capacitor, doesn't mean that they aren't paper capacitors. By the way, C12 should be replaced by a type X safety capacitor.

The six individual ceramic-form coils are very nice. The band switch looks like it is ceramic, too, unlike the stock phenolic switch in mine, and with a longer shaft so the decks are positioned closer to the coils. It also has two decks, instead of two sections in a single deck like mine:


Perhaps the coils and band switch are modifications made by some previous owner?

The audio choke was part of what was known as a phase shift oscillator. In conjunction with the capacitors in the circuit it would provide a 180 degree phase shift right around 400 Hz, and that was the audio frequency for the modulation and audio test output. I suspect those chokes were custom made for Eico, Heathkit, and other signal generator companies because there's no other place where they were used. Unfortunately they can and do go bad, and replacements went NLA decades ago. So what people did was to use the primaries of audio or TV vertical output transformers, or small power supply chokes where available, to try to come up with something "close enough" to work at a reasonable frequency. If yours works, I'd leave well enough alone.

I haven't tested the unit yet. I've been going over the parts list and this is what I found, it's missing T1, T2, C4, and L1 is not original it could be a replacement and the mounting holes don't line up. I've noticed C1, and C3 are dog bone ceramic capacitors, almost all the resistors are within tolerance and they made a lot of connections to the socket pins and some parts are just floating. I plan on restoring it but not right now.

Again, the parts list you have is not necessarily the parts list for this unit. Putting things in or trying to make it like something it’s not supposed to be could be the end of it. It does not sound like you have the correct manual for what is in front of you, so how would you get back to where you are now if you guessed wrong?

Given the wear and tear on the front panel, this unit was used a long time in somebody’s shop. So it probably should still work now, assuming the electrolytics and paper capacitors are okay. If you have the means to reform and test the electrolytic can, it might still be okay. If you can’t test it at its working voltage then disconnect it and put two new electrolytics in temporarily. The paper caps are probably leaky but they’ll probably hold up for a quick test. You’ll ultimately change them since with few exceptions, circuits don’t work well with leaky caps. The ceramic caps never go bad and should not be touched unless broken. Tubular ceramics are not made any more and often had special characteristics, so replacement is difficult if one gets broken. Micas fail but it is not common so it is best to leave them alone too unless troubleshooting points up a problem.

As for the resistors, yes they’re out of spec but that is more than likely due to being cold and having absorbed humidity. Measure them again after the generator has run a few days in its case and the resistors are still warm. Most if not all will come back into spec again. Only time I worry about a resistor is if it is discolored from overheating or won’t come back into spec after a reasonable amount of operating time.

What are T1 and T2? I don't see those part designators listed on any schematic or parts list for the 315.

I don't see C4 either, based on your photos.

T1 and T2 are the terminal post part #54007 and 54003 of the parts list model 315. But it not shown on this model.

With split gears in the tuning mechanism to minimize backlash.

Curly

I restored one of these a few months back. Really like it. doc

Wow, Doc, that's a beauty!