GE-408 FM unstable

6/30/2014 2:39:38 PMBill G.

I have a GE408. It has new capacitors three new tubes and a full alignment. It has great sensitivity on both bands... However...

If left alone the signal will deteriorate on FM. A touch to the tuning knob will usually bring the station back.
When the chassis was on the bench, I noticed that the tuning condenser was microphonic. The 12AT7 tube was definitely NOT microphonic, it was the tuning condenser.

My suspicions centered on a bad connection at the hub of the condenser. After spraying with tuner tonic and running AC through it with a 60 watt bulb, things improved, however, the problem is back after about 10 hours of playing.

I am considering two things. One is to remove the tuning condenser and run it through the dish washer. Another is to detach the ground connection for the filament of the 19T8 and run that connection through the hub of the condenser. The idea is that the AC would keep the connections clear like rejuvenating a vibrator.

Does anyone have experience with this problem?

Best regards,

Bill Grimm

6/30/2014 3:52:28 PMCV

Does the tuning cap rotor have spring "fingers" that ensure good electrical contact with the cap frame? If so, you might try abrasive-cleaning these fingers and their wiped areas. If there are no fingers, the cap may rely on only the ball bearings to provide electrical contact. This is somewhat iffy since common lube is nonconductive. There is a special conductive (silver-bearing) tuning cap bearing lube available specifically for this purpose. You could also try soldering a loop of copper solder-wick to the rotor and to the frame. I've seen that repair on some sets.

7/1/2014 3:00:36 PMBill G.

:Does the tuning cap rotor have spring "fingers" that ensure good electrical contact with the cap frame? If so, you might try abrasive-cleaning these fingers and their wiped areas. If there are no fingers, the cap may rely on only the ball bearings to provide electrical contact. This is somewhat iffy since common lube is nonconductive. There is a special conductive (silver-bearing) tuning cap bearing lube available specifically for this purpose. You could also try soldering a loop of copper solder-wick to the rotor and to the frame. I've seen that repair on some sets.
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Hi CV,
Thank you for the response. The tuning condenser does have the conductive spring. Cleaning that makes sense before doing the weird stuff.

Best regards,

Bill Grimm

7/1/2014 4:50:31 PMEdd

Sir Bill. . . . .

With your unit probably using the " bowed tuning fork " style of rotor grounding contactor as :

(But with no third RF section)

I usually have the best "non destructive" type of restoration of contact integrity by using multiple small strips

of white notebook paper, wetted with a Brasso solution.

(That white lets you see the actual duration that you are still picking up dark oxides.)

Then they are pulled thru the contact facings with an additonal slow, multiple repositions, as the rotor is then

run thru a full 180 degree
rotation to clean ITS moving periphral contact face to the fixed tensioned contact.

Then a final DEGREASING, with your option of relubing the contact areas or not , but for sure, do the bearing(s).

73's de Edd

You can have anything in life you want if you help enough other people get what they want.

::Does the tuning cap rotor have spring "fingers" that ensure good electrical contact with the cap frame? If so, you might try abrasive-cleaning these fingers and their wiped areas. If there are no fingers, the cap may rely on only the ball bearings to provide electrical contact. This is somewhat iffy since common lube is nonconductive. There is a special conductive (silver-bearing) tuning cap bearing lube available specifically for this purpose. You could also try soldering a loop of copper solder-wick to the rotor and to the frame. I've seen that repair on some sets.
::
::
:Hi CV,
: Thank you for the response. The tuning condenser does have the conductive spring. Cleaning that makes sense before doing the weird stuff.
:
:Best regards,
:
:Bill Grimm
:

7/1/2014 6:15:27 PMAdd On . . . . .

Sir Bill. . . . .

Looks like that specific unit will be requiring a "full pull" for unfettered full access of tuning condenser cleaning

. . . . if that is not already the case.

Plus, I should have known the unit to be having additional FM . . . . . since YOU always seem to drift to AM /FM

combinations.. . .by choice.

This one just doesn't happen to be one of your usual desired Zenith units, which I was not considering on this

Gentile Electrified unit.

The FM aspect is additionally having its variable capacitance built within that same tuning condenser.

S o o o o o o . . . . . are any of the experienced tuning quirks showing up additionally in the FM mode ?

How you liking the lighting accentuation being produced by its embossed clear lucite dial scale ?

Le tuning condensateur:

73's de Edd

THUNDERSTORM:

A chance to see just how MANY family children can fit under one bed.

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:Sir Bill. . . . .
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:With your unit probably using the " bowed tuning fork " style of rotor grounding contactor as :
:
:
:
:
:
:
:
:(But with no third RF section)
:
:
:I usually have the best "non destructive" type of restoration of contact integrity by using multiple small strips
:
:
:of white notebook paper, wetted with a Brasso solution.
:
:
:(That white lets you see the actual duration that you are still picking up dark oxides.)
:
:
:Then they are pulled thru the contact facings with an additonal slow, multiple repositions, as the rotor is then
:
: run thru a full 180 degree
:rotation to clean ITS moving periphral contact face to the fixed tensioned contact.
:
:
:Then a final DEGREASING, with your option of relubing the contact areas or not , but for sure, do the bearing(s).
:
:
:
:
:
:
:
:
:
:
:
:73's de Edd
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:You can have anything in life you want if you help enough other people get what they want.
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:::Does the tuning cap rotor have spring "fingers" that ensure good electrical contact with the cap frame? If so, you might try abrasive-cleaning these fingers and their wiped areas. If there are no fingers, the cap may rely on only the ball bearings to provide electrical contact. This is somewhat iffy since common lube is nonconductive. There is a special conductive (silver-bearing) tuning cap bearing lube available specifically for this purpose. You could also try soldering a loop of copper solder-wick to the rotor and to the frame. I've seen that repair on some sets.
:::
:::
::Hi CV,
:: Thank you for the response. The tuning condenser does have the conductive spring. Cleaning that makes sense before doing the weird stuff.
::
::Best regards,
::
::Bill Grimm
::
:
:

7/3/2014 8:17:45 PMBill G.

Hi Edd,
Thank you for the advice. Paper and Brasso is a great idea.
The problem only exists on FM, not AM.
I ran emery board over the contacts in two places, but did not like its thickness stressing the spring contacts. Paper, being thinner is better.

The lit dial is nice, however, there is history here that is unfavorable to the radio. As commonly happens these radios burned out their light bulbs. At some point the bulb that went into these went obsolete. However the higher wattage version of the bulb remained in production for GE refrigerators. Often these were used to replace the burned out dial lights resulting in a melt down. The damage is permanent.
I have two, both have this. I suspect ones without this problem are hard to find.
It looks nice and seems to perform almost as well as the Zeniths. I even used the Zenith alignment procedure to align it and it receives well.

On the bench it seems to be working. I even draped a towel over it to emulate the heat build up inside. It seems removing the case made the problem go away. I plan on doing the Brasso on paper idea before repackaging.

All the Best,

Bill