Troubleshooting A-80 motor

[Lucius1958]

So: I've been trying to see how I can get some decent performance out of the Edison A-80 motor.

Seller had said it had been overhauled by Victrola Repair Services; but I'm not sure how thorough the work actually was. For one thing, the governor pads were practically non-existent; I've since replaced the felt, and done some slight adjustment of the governor bearings. I've also tried adjusting the governor gear on its shaft to get the best mesh.

I've also replaced the leather on the turntable pulley, hoping that would even out the speed; I also rubbed some powdered rosin on the belt and both pulleys. So far, the speed remained rather erratic, sometimes coming nearly to a halt; the turntable usually needs to be 'persuaded' to start...

I've eliminated the belt as the source of the problem; so it is either a weakened mainspring, or some other sort of drag on the motor.

When the motor is running without the belt, I have noticed that there seems to be a periodic change in sound linked to the turning of the spring barrel: the purring of the governor starts to sound 'broken', and the worm gear / pulley shaft jumps a bit. How much endplay should there be in this shaft? There seems to be no way to adjust it, besides moving the governor gear...

Just to be thorough, I checked the bearings on the turntable: should there be a ball bearing on the lower end? I did not find one, though there was a spot that looked as if one should be there. This might be another source of friction; although the turntable seems to spin pretty freely as is...

The spring barrel turns smoothly, with no thumping: the 'rebuild' may have included cleaning & regreasing, but I'd better check.

It may simply be that the century-old spring is too weak to do its job properly. If I get it replaced, is it possible to get one that's just a tad stronger?

Any advice would be appreciated.

Bill

[wjw]

Since I know nothing about this motor, I think a post is in order.

Seems to me that when the governor sound changes and the worm gear jumps, there is a loss of power from the gear driving the worm. If this is so, you could mark the gear to see if it's in the same position every time the governor misbehaves. As to the ball bearing in the bore- no harm in trying one whether it was designed with one or not.

[Lucius1958]

I've replaced the ball bearing on the turntable spindle, and tweaked the governor a bit more; but the problem persists.

I've added this video to show the motor's performance ; you can clearly hear how the motor is periodically slowing and recovering. As I've said, the frequency deems to correspond with the rotation of the spring barrel; so it doesn't seem to be a belt problem.

[youtube]http://www.youtube.com/watch?v=Fqd3gkh_bu4[/youtube]

Any advice?

Bill

[Lucius1958]

From what I hear from APSCO, it may be a problem to replace the mainspring, as the 60/80 models used a unique size. Does anyone know of someone who might have the facilities to fabricate such a spring if necessary? And how does one determine the strength of a spring, aside from installing it in the motor?

As far as I can see, my options are:

. Finding an existing mainspring, of proven strength, from another A-80 (or B-80 - did they use the same spring?)

. Having a spring specially fabricated

. Finding some way of adapting another mainspring, and probably its barrel, to the A-80 motor

All of these are, of course, dependent on diagnosing the mainspring as the true source of the problem. The first option seems most likely - if I can be certain of the replacement spring being of proven strength (see above). The second may be possible, but quite expensive: the third seems quixotic at best.

As I've mentioned before, I'm wondering whether the large amount of endplay in the worm gear/pulley shaft might have anything to do with the speed problem. Should it have that much? It seems to be about 1/16", if not more; I might try inserting a spacer underneath the governor gear, to see if that has any beneficial effect....

So, anybody have any ideas?

Anybody?

Bueller?

[gramophoneshane]

I really dont think the spring is the problem. It seems to be occuring about every 30 seconds, and lasting for 4 or 5 seconds before picking up speed again.
A weak spring will usually behave differently, either slowing during loud or worn passages of a recording, or running out of oomph (& not recovering) towards the end of a record.

1/16" end play does seem a little excessive so there could be a problem with the governor, but with the regularity of it slowing, and for around the same period of time, I think it's more likely to be wear in a gear or bearing, or a combination of both.
The first gear I'd check is the main drive gear off the spring barrel. I think you'll find 2 or 3 teeth that have some wear/damage, and it's taking 4 or 5 seconds for these worn teeth to pass the gear they mesh with.

I'm not familiar with this particular motor, so I dont know if the drive gear is attached to the barrel or the centre of the spring, but I'm guessing it takes around 30 seconds for the gear to make one full rotation.
If not, I'd watch the motor run & look for a gear that does take 30 secs to turn 360 degrees.
I normally put a mark or scratch on the gear where I suspect the wear might be, so I've got a starting point to examine the teeth once the motor is pulled down & the gear is thoroughly cleaned.

[kirtley2012]

why dont you just cheat and buy a wrecked DD machine and remove the motor or even buy a whole motor, then the problem is solved! if not i am sure you will find someone parting out a A-80 who can give you a spring!

[Lucius1958]

why dont you just cheat and buy a wrecked DD machine and remove the motor or even buy a whole motor, then the problem is solved! if not i am sure you will find someone parting out a A-80 who can give you a spring!

Well, the problem with swapping a motor is that it has to be compatible with the A-80: anything from other DDs (except perhaps a B-80) would require major surgery......

I would accept another A-80 mainspring, if I could be sure it was up to par....... hence the question about testing.

Bill

[Lucius1958]

I really dont think the spring is the problem. It seems to be occuring about every 30 seconds, and lasting for 4 or 5 seconds before picking up speed again.
A weak spring will usually behave differently, either slowing during loud or worn passages of a recording, or running out of oomph (& not recovering) towards the end of a record.

1/16" end play does seem a little excessive so there could be a problem with the governor, but with the regularity of it slowing, and for around the same period of time, I think it's more likely to be wear in a gear or bearing, or a combination of both.
The first gear I'd check is the main drive gear off the spring barrel. I think you'll find 2 or 3 teeth that have some wear/damage, and it's taking 4 or 5 seconds for these worn teeth to pass the gear they mesh with.

I'm not familiar with this particular motor, so I dont know if the drive gear is attached to the barrel or the centre of the spring, but I'm guessing it takes around 30 seconds for the gear to make one full rotation.
If not, I'd watch the motor run & look for a gear that does take 30 secs to turn 360 degrees.
I normally put a mark or scratch on the gear where I suspect the wear might be, so I've got a starting point to examine the teeth once the motor is pulled down & the gear is thoroughly cleaned.

Thanks for the advice!

Just to clarify: the end play I mentioned is not in the governor shaft, but in the worm gear/pulley shaft that engages directly with the spring barrel. When the motor is running, with or without the feedscrew engaged, this shaft periodically clicks several times, during a specific phase of the barrel's rotation (yes, the barrel takes about 30 seconds to rotate fully).

I can see no evidence of wear or damage in the main drive gear, which is bolted directly to the barrel. The feed screw, which turns with the barrel, does not appear to have any significant damage either.

[kirtley2012]

you could always try bending the existing spring outwards to make it stronger, that might work but it might not, possibly worth a go!

[Lucius1958]

Update: I spent some time disassembling, tweaking and reassembling; and now the speed problem seems to have abated. I'm not quite sure what did the trick - it's not absolutely 100% steady - but it's certainly a vast improvement.

One of the governor bearings got damaged while I was trying to get it free; so I'm using a jury-rigged repair. I'll see what happens once I get something more suitable...