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I think my last question was too open/ended. 

I've decided to try testing my diodes since it can apparently be done with them in place. 

Are there any other "low-hanging-fruit" things I can check?

I'm getting no signal from the reed bar - in fact unplugging it has no effect..  just a loud 60hz buzz from the speaker (or headphones) that does not change when I change the volume or vibrato.

I assume I'm getting the wrong voltage..

Thanks!

Well, I replaced the can caps, and I'm fairly confident I did everything right based on your very thorough instructions..

Unfortunately, the caps were not what was causing the malfunction I have been trying to hunt down.

What is frustrating is that I had the piano working several weeks ago and was just trying to eliminate some hum, sone radio interference and sone scratchy pots. 

Somewhere along the line something went very wrong and all I get is a loud noise - like when you plug a bad cord into an amplifier - the noise is not affected by playing the keys, adjusting the volume or vibrato - if I put headphones into the headphones jack, I get the same sound through the headphones. In fact, unplugging the pickup cable from the amplifier makes no difference at all.

I don't know if it's something I did or if some old components failing now either by coincidence or because I disturbed them.  Here is a little history of what I've done, how the malfunction developed and some of the things I've tried - in hopes it will ring a bell and someone will recognize these symptoms..and perhaps a cure:

I replaced the vibrato lamp - vastly improved the strength of the tremolo even the audio signal in general.

I replaced the on/off volume pot - got rid of some scratchiness.

I replaced the neon pilot bulb which I had accidentally destroyed while working on the wiring harness.

I installed components from a Vintage Vibe amp rebuild kit - resistors, transistors, capacitors - not including the can caps. This really didn't make as much difference as I had hoped, but the piano worked, though still a lot of hum.

I then replaced the two prong plug with 3 prong IEC and this is where something began to go wrong. When I first tried it out, the piano worked but I got some loud pops and noises and the signal was cutting out - there were certain notes that seemed to trigger it, so I figured I had gotten something on the reed bar that was shorting it out.

I used compressed air and a vacuum to clean everything out but got no improvement.

Someone suggested maybe it was bad can caps which had never been replaced - I couldn't see why they would suddenly fail now after 60 years, but when I touched the cans there were loud crackles and pops - so I replaced those - now the crackle pop sounds are no longer happen when I touch the cans, but now the malfunction is constant - I can't get any tones from the pickups at all - just a loud noise like something is shorted.

Is it possible I damaged the transistors or the transformer when I cut the hole for the IEC with a Dremel? There was aluminum dust - which I clean off - at least everything visible - but what if some found its way inside the transformer - or could the vibrations from the dremel have disturbed something?

I am totally stumped. Is there anything about what I described that could narrow it down, or binary tests I can do to rule out various culprits, or narrow down my list of suspects?

For example, can I plug something other than the reed bar pickups into the rca input jack on the amp to prove whether it's the amp or the reed bar that's malfunctioning? 

Or can anyone tell be what it's supposed to sound like with the reed bar unplugged?

What would be the symptoms of a bad transformer or bad output transistors?

Any advice you can give me to track this down would be much appreciated!

Thanks,

Kevin

I finally got my components from Mouser after and installed one of the the 2200uF caps under the -32v can as instructed.

I also had no trouble installing the 470uF cap under the +32v can..

Then I hit a snag with the other 2200uF cap when I found there were four wires attached to the terminal marked with a half circle, not 2.

It stands to reason that I should cut off all four and solder them to the positive leg of the new 2200uF, but rather than assume, I figured I'd ask and wait for clarification.

Thanks again for all your help!

Yes, sorry to give you a scare with my dumb comment about trying various grounds - I'm less reckless in my actions than with my comments. 

What I did - with some success, is connect the 930's 1/4" jack with a Wurlitzer 270, the 200a in a walnut butterfly cabinet. The amp is identical to the 200a, but happens to be factory fitted with a 3 prong grounded AC cord.

With this combination, the hum got a LOT quieter.. so just being connected to a grounded instrument did the trick.

I think I'll call that a win - thanks guys!

A treasure trove!! Thank you.

My much simpler floating jack only had two conductors, so I'm not sure how to ground it, (see picture). Also, I'm not sure what good it would do, since a 1/4" audio plug (TS) only has two conductors as well (inner multi-strand wire soldered to the Sleeve, and outer braided multi-strand wire soldered to the Tip). 

I'll experiment with a test wire from the amp chassis to various points on the floating jack and see if this solves my buzz/hum problem - if so, I'll mount a proper grounded jack in the cabinet, and perhaps a grounded AC plug as well, and do away with the duel purpose Amphenol connection altogether.

Please let me know if either of you think any of this sounds like a bad plan, as I don't really understand grounding..

Thanks again for all your help

The following comment from 2021 about adjusting the strike line intrigues me to no end. But which bolts were loosened, exactly how was it tweaked and adjusted? Do 'high side" and "low side" refer to the left and right halves of the reed bar, or the upper and lower pickup plates? Were they shimmed or what? What is meant by "first" and "later".

"Now I have loosened the harp bolts, shifted the high side first and lower side later, and what a difference! A few minimal tweaks make all the difference!"

If anyone remembers this post and knows what was done, I'd love to try it!

Thank you so very much - thus is exactly the tutorial I needed. The photos and verbal explanations will get me through this, since I get lost reading schematics.

I see you installed an EIC panel plug on that chassis - I did that too, but I had a few questions you don't mind:

1) I put the live to the line switch, and the neutral to the transformer - is that right or should it be the other way around?

2) Does it matter which direction the fuse is wired? I've seen it both ways.

3) I removed my phono jack and cut a hole for my IEC there. One of the phono jack's posts seemed to served as a bridge for several wires and also seemed to be grounded to the chassis, so I left those wires connected and ran a ground ti the chassis. Does that sound right? There was also a long wire that went from that same post all the way to the other end of the circuit board where the reed pickup connects - I could figure out no purpose for this with the phone jack gone, so I removed it. I see that wire is missing from your board too, which gives me hope that I did the right thing.

Sorry of that is too vague, and thanks  for your patience and any guidance you can give me.

Thanks for this very helpful information.

The first difference I notice is that the 930 schematic has a separate control box, complete with an on/off switch, a pilot light, a two prong ac cord and a grounded 1/4" jack - but grounded to what?

Instead of a box, my 930 has a floating jack and a two prong ac cord combined in a 6 pin Amphenol socket (only 4 pins used). It sounds like something a prior owner rigged, but actually it looks kind of professional - I always assumed it was factory, but now that I see the schematic shows a control box I'm thinking maybe this is a hack job after all, and maybe explains my hum/buzz.

In the amp itself, the green and black lines going from the Amphenol plug go directly to the circuit board with no grounding that I can see.

So do you think if I just install a jack and ground it to the chassis that might solve my hum?

Thanks again!!

I have one of these 930s that works great but it's noisy.. a pretty loud 120hz hum/buzz. I saw a post on here from about 10 years back regarding one of these rare birds and am looking for someone that has one who is willing to share a photo of the actual circuitry under the amp.

I've had great luck working on these amps by comparing mine to pictures of the actual circuitry.. I've spotted cases where a prior owner wired something wrong.. but when I look at the schematics I just don't know how to interpret them.. 

Like they say, a picture is worth 1000 words! 

Thank you for any help you can provide.

I need to replace the capacitors in the two cans. I can read what's written on the outside of the cans.. and the Wurlitzer schematic. Vintage Vibe and Tropical fish sell kits, which I've bought in the past, but in this case, I just want specific components. Can anyone recommend a good source?

Also, any experiences you can share te doing this upgrade would be very much appreciated. I know the new caps are usually added below the can rather than putting them inside.

Pictures of the underside of the amp would be great too, as I am not great at reading schematics and the actual circuitry isn't always consistent with the original schematics.

Thank you!!