Sruddy's FM-200-B Restoration Thread

[sruddy]

There are no provisions for individual channel output adjustments on the FM-200B. Try this:

1. Operate the tuner in mono mode. If the imbalance is there, it is due to some issue in the output amplifier circuits.

2. If the imbalance is there with the Output Level Control at a mid-range setting, then the problem could be the control itself. Operating the tuner (still in mono) with the Output Level Control up full will eliminate the control as a possibility. Any imbalance with the control in this position then must be due to some issue/component in the immediate vicinity of the output amplifiers -- or the following amplification/speaker equipment.

If the imbalance is only there in stereo mode, then the MPX decoder becomes ground zero for the hunt.

Dave

Dave I did the mono test, seems totally fine! I think I may have had too much wine when I made the imbalance comment, Ha Ha. Also I don't have my speaker shelf built yet so the left is only about 18" from my head.

I have contacted the guy that does my alignments and the first thing he asked was about the shape of the Nuvister tubes. Since I have yet to get an adapter or make one for my Hickock 752 I went ahead and ordered a matched pair of NOS RCA from Brent Jesse. I will send them along with the originals for him to play with. I also replaced V100 and V102 as V102 was just at minimum. I found some RCA JAN12AT7WA for cheap, but I'm not sure if that position benefits from a military tube.

This tuner can be sooo quiet it's scary!!. Here is a quick photo I took last night before bed. Sometimes a little wine gets the creative juices flowing!!

 

[dcgillespie]

Sharp looking tuner! If you do have it aligned, make sure your tech has had experience with specifically the 200B. While the general alignment procedure itself is quite typical, having a correct alignment is much more critical with the 200B than many tuners, as the AFC circuits and FM Automatic stereo switching circuits must all interact properly with the basic tuner circuits, so that they all work to augment rather than work against each other. An improperly performed alignment can easily upset the interaction of these circuits. It is not uncommon for many FM-200B's I've seen to tune in a stereo station just fine, but if any of the AFC functions are on, they will then pull the tuning out of stereo lock, so that the tuner reverts to mono operation. Unless the tuner clearly indicates the need for an alignment -- as indicated by distorted sound, lower than normal signal strength indication, or poor stereo switching/AFC interaction as noted above -- then I would consider leaving well enough alone. Changing any of the tubes will not upset the alignment of the 200B.

Dave