James,
I never played an H but it is basically the same thing as an E except for fewer notes/pedals of course. If the organ has been played regularly it should be working farily well; it it has been sitting around for years unplayed you may have issues with filter caps in the power supply (no surprise there...). These are relatively simple instruments - no ICs, etc. Most repair parts are just your standard components (caps, resistors, etc.) and can easily and cheaply be acquired.
I have many Gulbransen service manuals. The ones for the early models are simple little books or just pages stapled together with a few schematics and theory of operation. In fact, many of the old spinets don't even have their own manual; there is a "spinet technical manual" that basically covers all of them. The manuals for the later models, however, are practically encyclopedias; that gives you some idea as to how "simple" the earlier instruments are.
These were very well built instruments and there may be no problems with it at all. But just in case, here are somethings to look out for:
The tone generator units may need some servicing; the 230 ohm emitter resistors can drift up with age and you will know this if you get "sluggish" notes (they start soft and "fade in"; they may even be dead altogether if the volume tabs are not engaged - if you can bring a dead note back to life by engaging a volume boost tab then that cinches it). But if there are no sluggish notes you're good to go. You test for this by only engaging a single footage stop (no combos, etc.) and try every note. Switch to a higher footage to test for notes at the end of the compass.
If the reverb/sustain does not work well the sustain caps need replacing; again, nothing very complicated (just tedious work). These are on the TG units. You may also need to replace the anti-keyclick caps on the TGs if necessary. But, to give you an example, the TGs in my Model E worked just fine after I replaced the emitter resistors to get rid of some sluggish notes (if you replace a few, you may as well replace all of them); I did not need to re-cap them at all after 40 years.
FYI only one set of TGs is used for the entire organ (both manuals and pedals) so if you have the same troublesome note appearing again and again (i.e. the same footage note on both manuals; the same note when played on a higher footage stop/lower octave key, etc.) you can be sure that the TG needs to be looked at.
Not sure if that vintage of H has a tube amp or solid state; if solid state, the AM2 amp is pretty stable, though there is a 75uF radial cap you should switch out with a new 82uF.
Notes cutting in and out usually just indicates dirty contacts - just play the note several times over and over and that will go away (you notice this more on the notes that are rarely played).
I can't speak for the rocker stop mechanism as both of my Gulbransens use the tab stops.
Again, the organ may be fine. If it needs servicing it would be relatively simple work to do in most cases, if you have done this sort of thing before. Is it worth it? If you like these organs I would say yes.
- Jim
Jimmy Williams
Gulbransen Model D, Leslie 204, hobby organist/technician