AMI G-120 amplifier recap

AMI is up and running, but no sound, so I ordered a recap kit and tubes from Jason Tisdale. Jason provided a wire schematic with the cap kits, which is very helpful, especially if you do not have a manual for your jukebox. His schematic actually show an additional .02mf capacitor and 1k ohm resistor that is not shown in my schematic, however, it is installed in my amp. Must be modification/correction that was added after the manual was printed.
My concerns are R/T small ceramic caps that I removed from the amp were marked 330 and the schematic shows .00033, which should be a 331. I have the 331 replacements that were provided, but 330 caps came out of the amp. I have read that up to 100% increase in capacitance is not a problem, but they seemed to have gone significantly more than that. Was there a design reason or supply reason they installed the 330? If no problems are anticipated I will install the 331 replacements, otherwise, I will get some 330 caps to install.
Thank you, Craig.

Craig, the only 00033 caps that i see are one on the "treble range" sw at the "full" position. and the other is across the signal coming from pin-1 on the driver/splitter 12AU7.

I eliminate that R&C on the full position as it still attenuates treble and causes a peak in the loading of the pickup. You won't want to reduce the treble on any of those machines.

The second one is optional too though I would not go above .00033 -and even that will probably affect whatever highs are able to get through.

These old machines did a lot of attenuating of the highs in anticipation of worn styli and ruined records (which that unbalanced tonearm contributed to). Whenever I rebuilt something like this I put it under test for response and build a set of response curves. Juke amps always have a lot of treble cut in them and I usually get rid of, or modify most of it.

Those amps have idiotic switching of the B+ between records and that means the full inrush hits the filters everytine the amp unmutes.

For my H & I I removed that and placed a relay connected to the scan control that switches an AC outlet on at the beginning of a session. The amp is plugged into that and goes on and remains till the mech scans out. Only the muting contacts are still used.

I never really liked the sound of those amps as designed, so I redesigned for a standard cathode follower preamp output, used a dual tapped 25K volume pot and set the R&C values on the taps to suit the machine speakers. This is probably more than you'll want to bother with.

The biggest improvements you can make is adding a proper counterweight on the tonearm and using a newer pickup. Those two steps offer a great improvement in record life and sound.

There are a two pic's on that mod here: http://s1192.photobucket.com/user/Rob-N ... t=3&page=2

Rob

Rob,
You mentioned pics of modification and had a link, however, you discussed 3 different modifications and there are a bunch of pics in your photobucket. Are you talking about the counter balance mod. I see weighted tone arm pics, but I do not know where to obtain those types of parts. It looks like it can be attached by drilling a hole in the back of the arm and putting a nut on either side of some threaded stock to hold it in place. I would also be interested in the schematics for the other mods you mentioned, if you have them available. I am not as knowledgeable as you folks, but can follow most schematics and I'm fairly safe with a solder gun.
Thank you again for the advice, Craig.

Craig, the only mod shown in the PhotoBucket link is the tonearm counterweight. that particular one cam from a post 1966 Seeburg arm assembly (I had a box of odd parts). I've used various forms of weight on these old machines. In cases where looks didn't matter I just used large washers with bolts at each end. On the Continentals I had to cut off a part of the mach dress cap to clear the added counterweight. I did a careful job of it and it looked fine.

If there is one mod I'd suggest over all it is to counterweight the arm. this will allow a better pickup and greatly reduce wear.

The amp mods were just done on the fly (which means I was lazy and didn't keep notes). I think I remember what was involved, and we can go into that later.

Rob

Thank Rob, I will look for an old tone arm I can swipe the counter balance off. Swap meets and garage sales might have an old phonograph that I can cannibalize. Is there any way to use a spring like what is used on other tone arms? I can't remember the tone arm arrangement on my F and G units, I have been trying to get the Seeburg C unit up an running correctly.
Thanks again for all your help, Craig.