[Ron Ramirez]

So I've been restoring a Fisher 100-R AM/FM tuner from 1960. Only five paper film "dog turd" caps (they look like brown Orange Drops but they will require replacement), three electrolytics in one large can, and a selenium rectifier that must be replaced with silicon. Easy to restore. The only drawback of the 100-R is the 6G-E12 dual eye tube used as an FM and AM tuning indicator. It has become "unobtainium". Of course the 6G-E12 in my 100-R is weak

[Arran]

I wonder if you could substitute a 6AL7 for one of those 6G-E12 tubes, both have an octal base, and the display is similar, but not the same obviously? This is not the same as the 6G-E12A which is like a 6AD6 with a square target.
Regards
Arran

[Ron Ramirez]

I'm afraid not, Arran. The 6G-E12 is, in effect, two 6E5s in one envelope - two triodes, two targets.

I suppose a 6AF6G could be made to work if one could figure out how to rig up two transistor amps in lieu of two triode amps? I think that might be a bit above my pay grade, though.

I have my 100-R up and running. I only need to rebuild its three section electrolytic can for safety and reliability. Its 6G-E12 is visible in daylight but it is dim.

[Arran]

Since this one obscure eye tube uses a sort of bar graph display, and dual triodes, I was just thinking that maybe an adapter could be made using a pair of EM83s (Soviet version 6E3p of course), but the filament current for each would be 270 ma so slightly more load on the transformer . Then again the EM83 has two triodes inside so you may not need the second tube unless you just want the dual bars side by side, not sure about the 6E3p. From what I was reading about the 6AD6 or 6AF6 in the few radios that used them they drove the eye tube from the plate of the IF amplifier rather then employing another tube. However the filament current of both tubes is only 150 ma, which was why they were also used in some Belmont built Airline AC/DC sets, so you could add a dual triode tube to drive it as the 6G-E12 uses a 300 ma filament, still an engineering project but not impossible. You could still go the 6AL7 route maybe, but then you would only have one operable shadow, I have to go that route when replacing a Rogers 6X6 with a 1629 since the prior has two shadows and the latter only one.
Regards
Arran

[Ron Ramirez]

In the 100-R, one half of the display is for FM tuning; the other half for AM tuning. Both are illuminated all of the time because the 100-R was designed and built before the FM Stereo standard was adopted.

Back in ye olden days of 1959-61, many tuners and receivers (including this 100-R) could be set to output AM and FM at the same time - AM in the right channel, FM in the left. This provided a sort of primitive stereo reception but required radio stations to broadcast one channel on AM and the other on FM.

Other Fisher tuners of the time, as well as their TA-600 and TA-800 receivers, utilized separate magic eye tubes (EM84) for AM and FM. When the unit is set to AM, only the AM magic eye is illuminated; when on FM, only the FM magic eye; when set to "FM-AM" both are lit up.

So I wonder why ol' Avery used a tube that was seldom used even then (6G-E12)? Sure, it accomplished the purpose, but he must not have been thinking about replacements. And the tuner was rendered obsolete about a year or so after it was introduced with the adoption of the GE-Zenith FM multiplex standard in 1961.

[Ron Ramirez]

Oh, I forgot to mention: The 6G-E12 produces a dual fan display, not bar graphs.

I'll post a schematic later. Edit: Here it is (warning - large file - 2.2 MB):

http://www.philcoradio.com/images/phorum...R/100R.jpg

[Arran]

Ron;
  The only reason I can think of is cost perhaps? Maybe some sales representative made Mr. Fisher, or his chief purchasing agent, an offer on a rail car full of 6G-E12s, so they used them on their lower end tuners rather then a pair of EM84s. It's sort of odd that they would not have used something like a 6AL7, those are easy to find even now because G.E developed them as a tuning indicator tube for the post war market, but the new design never really caught on, and the magic eye craze was pretty much over by then anyhow. I think that the only units that used 6AL7 tubes, were G.Es, Dumont TVs and combo units, and some RCA Orthophonic AM/FM Hi Fis, I did have a Northern Electric AM tuner out of a combo unit that used one but that doesn't really count. EM84s are one of the magic eyes with a fan shaped display are they not?
Regards
Arran

[Ron Ramirez]

The EM84 has two bars, left and right of center, that meet in the middle on very strong stations.

[Ron Ramirez]

...an offer on a rail car full of 6G-E12s, so they used them on their lower end tuners rather then a pair of EM84s.

Forgot to mention...Fisher's first "stereo" tuner (AM/FM simulcast, no FM multiplex) was the 101-R which used dual EM84 magic eyes. The 100-R replaced the 101-R around 1960. In 1960 Fisher only had the 100-R, FM-100 (FM only, EM84 indicator), and FM-50 (also FM only, EM84 indicator). Plus the 100-T and 202-T which were tuners with stereo preamps.

The FM-50 was the low end model; the 100-R was their best tuner (only).

In 1961 along came the 202-R to replace the 202-T; the 202-R had no preamp. The 100-T was discontinued.

And then in late 1961 the new 1962 models came out with the new GE-Zenith FM multiplex system. All of the old tuners were replaced; the FM-50-B replaced the FM-50; the FM-100-B replaced the FM-100; and the R-200 replaced the 202-R. There was also now an FM only version of the R-200, the FM-200-B.

Through all this, the 100-R is the only Fisher tuner to have used the 6G-E12 tube.

[Arran]

You're right of course, the EM84 was the tube with the double ended single bar style display, it's rather funny in that the EM85, which I would have guessed came out later due to the number, uses a similar fan display to an EM80, but it has a dual action to the fan. The European (actually Phillips) numbering standard always mixes me up, it's also confusing because they numbered tubes using that standard that have no connection to Phillips at all, such as the war time German metal tubes that look like an over sized 6H6.
Regards
Arran

[mattdude0]

I have a very weak 6GE12.  Only the right side (AM) produces a display.  Can I test this tube in my tube tester?  If so then instead of 6.3v I could run it on 7.5V briefly to see if that boils off some impurities on the filaments.  I know some people used this trick on CRTs to gain some additional picture quality.