[flatheadjr]

I just picked up this early automotive fm converter that's made by Automatic. I can't seem to find much information on it, all I have found are some photos and a tube diagram from the radio museum. Anyone out there happen to have a schematic for this unit? Someone had pulled the antenna lead from it and replaced it with just wire. I'd like to make sure I put a replacement in the correct location.

[Radioroslyn]

A bit of an odd ball set as it uses tubes that operate from 12vdc for the HV. Circa 1961or so. Don't have a manual but what you are looking for is a Sam's Photofact #514-6. It will have all of the service info. Sometimes the Sam's can be found at the library or a post over on the barking dog might turn up a copy if no one here has it.

[flatheadjr]

I found a couple sources for the schematic on this unit but as usual they were asking 2 to 3 times as much for an electronic copy when I have paid much less for more information on the set of bulletins I got from one of the Philco guys. I believe its the ECC86 tube in this unit that generates the high voltage for the other tubes to operate but I could be wrong.

[Radioroslyn]

Nah it's another 12v plate tube too.    http://www.r-type.org/exhib/aaa0172.htm

[flatheadjr]

So I finally powered up this little unit but I have no clue if it is working. I had to replace one tube as it had a wrong one in it. I put 12 volts DC to it and while warming up it would draw 1.20 amps, and after the tubes warmed up it was around 1.06 amps of power draw. I'm guessing this would be normal for this unit as I do not have the specs for it.

[Radioroslyn]

If you can post a few pics with it out of the cabinet we can probably figure it out. The basic idea is that it's a FM tuner that the FM audio signal is transmitted onto the AM radio. The large wire coming out of the back goes the AM radio's ant plug. On the back of the converter there's hole in the bottom right corner, that's where your car ant would plug in. Power it up w/it plugged into a radio and ant. Set sw for FM or AFC tune the AM till you a hissing sound then tune in the FM tuner.

[flatheadjr]

So I was able to locate a schematic for this unit, and was able to verify the make shift radio antenna fortunately it was connected in the right spot, I made the correct connections to the antenna on my tester radio found where it tuned into which was right around 870 on my AM unit and surprisingly it works. The only problem I did find is that it goes okay to the bottom end of the scale and picks up all the local stations there, but it doesn't seem to go past around 103.3, so would this be an alignment issue, or a dirty tuner?

[flatheadjr]

https://app.box.com/s/rfdmm2obwxt9hw8qmye56wh27rsl6rsn
Here's a link to the schematic.

[Radioroslyn]

I would think that it maybe a weak 6GM8. The tuning is not done with a tuning capacitor but be moving a metal slug though a coil. This is called inductive tuning. So there isn't much to clean. A8 looks to be the oscillator adjmnt this is use the set the frequency at the high end of the band, A9 is the rf adjmnt this will make the stations near the the high end of the band louder IF it is out or alignment. Would clean up the tube sockets by spraying some Deoxit on to the tube pins and then inserting them a few times. Also switches too.

[flatheadjr]

So I'm not sure what the 6GM8 is, but I did some cleaning with the tube sockets, and cleaned the contactors and still have the same result, I only get up to that 103 area and it comes in fairly loud compared to anything else, not quite sure what else to look at.

[Radioroslyn]

>So I'm not sure what the 6GM8 is

It's the US number for the ECC86, that's one those foreign number.

[flatheadjr]

I did see 2 different numbers on that tube and it also said made in Holland on it, I'll see if I can locate another and see if changes anything. Seems like any of the tubes that I did look up for this unit were fairly cheap anyways.

[flatheadjr]

One other thing I wanted to point out is when I go to tune this unit it is sensitive to touch. When I hold in to the dail knob any station it is tuned into fades out and as soon as I release the knob that station comes back on. What would cause that?

[Arran]

 That reminds me, I have a few late 1950s and early 60s car radios I need to test that use those sorts of tubes with the 12 volt plate and screen voltages. I think that they work on the space charge principle, but in most of the North American car radios the final output is a power amp transistor, not a tube like that write up about the ECC86 mentioned.
Regards
Arran

[Radioroslyn]

One other thing I wanted to point out is when I go to tune this unit it is sensitive to touch. When I hold in to the dail knob any station it is tuned into fades out and as soon as I release the knob that station comes back on. What would cause that?

Could be a poor earth ground. Mounted in a car there is a bit more metal around it help stabilize it's metal cabinet to ground which you don't have sitting on the work bench. There also could be some effect between you touching the knob/chassis and the ant. This may cause cause the mixer/osc to pull a bit. These 12v HV tube or space charge tube are not quite as robust as regular tube w/normal hv on them and can be a bit squirrely

.