Trimmer Capacitor not on Schematic

The Sam's is very comprehensive. Details how and when to adjust this trimmer will be in the service notes section. Almost always a trimmer is for the high mhz of the band. A slug is for the low end.

If there is but one adjustment generally the center of the band.

Alignment must be done in the order given.

There may be a requirement for the alignment be done with the battery present below the radio. If there is no battery a sheet of aluminum in the battery compartment taped to the underside will work.

Unless specified, use the lowest generator setting, 30% modulation and 400 - 440 hrz modulation. A analog AC voltmeter is usually connected to the speaker output terminals.

The signal must be kept very low to prevent the AVC from quieting the receiver. Any RF noise in the shop/lab will effect the AVC.

IMHO Sam's will send (another) 381-16...

Keep in mind that Zenith may have made a production change after Sam's documented the radio...

Only a full service Zenith dealer would have production updates. Then again, it may not have made it to publication...

You may find this topic on the ARF to be most helpful, overall.

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YMMV

Chas

Removed the bandswitch assembly from the radio chassis to look at the connections. That trimmer capacitor functions as the 'A5' trimmer on the schematic. The A5 is labeled as being located on the front section of the variable tuning capacitor but is not located there on the B600 chassis. No adjusting trimmer is located on the tuning cap first section at all--no screw, top plate, or mica insulation. Just a wire soldered to the bandswitch which this small trimmer connects to.
Bob

Thanks. I've arranged to get a schematic from SAMs and I'll have it in a couple of days. (I have one for the A600). The problem is the very thing that drives repairers and suppliers nuts. The only number difference is the case Model number (B600). The Sam's list gives the same chassis number for both the A600 and B600 models. It certainly is in the right area for the band you're indicating. If I nail it down I'll post it.
Bob

Looks like the osc trimmer for the 4-9mhz band.


Need Sam's Photofact (Set 381 - Folder 16)


There should be an index for all the Sam's manuals here:


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A copy is available from Sam's, copyright is still on the Sam's of that era.

YMMV

Chas

I'm working on a B600 model Zenith Transoceanic tube model. Chassis 6A40; Schematic I have is 381-16, but is labeled as an A600. (Probable cause of the question). There is a trimmer capacitor, Part Number 22-2928 stamped on the trimmer which doesn't appear anywhere in the schematic. It is connected to the bandswitch tower and chassis (not B-). The location is just to the left of coil L18. I can't find that part number on the schematic parts list or diagrammed anywhere on the schematic itself.
I need help in understanding 1) where this trimmer is located in the circuit and 2) how does this trimmer fit into the alignment procedure? If I can get ahold of a B600 6A40 schematic (hopefully showing the role of this trimmer) that would be helpful as well. Thanks.