Johnnys Junkyard Gem
Posted: Thu Jun 01, 2023 12:28 pm
I posted about this when it first landed during lockdown. After languishing in the garage for over 2 years I decided it was high time I fixed this Gem Mini Deluxe I bought so I can play it. This is how it looked when I went to get it from the other side of the country (not far in the UK):
And fresh out the garage...
When I picked it up only half the keys played and a bunch of other obvious things. I took the time to clean and service all the trigger rails and stuff and ended up with a 99% functional vintage analog organ for £40. The only thing causing issues was the E tone card. It rarely passed a note, and when it did it was very distorted and missing one of the octaves.
It's quite a complicated beast...
...but the tone cards themselves break them down quite nicely into bite-size chunks:
I can't find a schematic anywhere for it so just have had to go by educated trial and error, along with looking how Vox Continentals were made (same factory but not the same internals annoyingly). I accertained that is was either the tin can transistor up top or one of the 4 Silicone transistors. Through trial an error I established it's one of the MTJ00109 type. Online organ guides have the replacement for this as 2N5449 (NPN) which I actually had 3 of already. Those went in and the problem persisted, but got slightly better.
Not having any more to hand I stole one from the adjacent cards and that fixed part, but not all of it
So, currently, the E card has it's 3 originals put back in it, plus the one from the F card...and now it works great. But not the F I managed to rummage around and the only other NPN I had was this big ol' 40w thing that I wedged into it for the time being. It works, but it's not quite right. You can see it on the right hand side with it's little heatsink thing poking out like a plumbers asscrack 
Further reading showed that BC549 transistors are a suitable fit, so I ordered 100 for £5 delivered. Lets see if those get me any closer!
Once that's fixed and I'm happy with that I'll turn my attention to giving it a proper recap, and take a look at the vibrato circuit as it has an underlying noise in it that's unaffected by volume (likely some cap noise).
Fun times.
And fresh out the garage...
When I picked it up only half the keys played and a bunch of other obvious things. I took the time to clean and service all the trigger rails and stuff and ended up with a 99% functional vintage analog organ for £40. The only thing causing issues was the E tone card. It rarely passed a note, and when it did it was very distorted and missing one of the octaves.
It's quite a complicated beast...
...but the tone cards themselves break them down quite nicely into bite-size chunks:
I can't find a schematic anywhere for it so just have had to go by educated trial and error, along with looking how Vox Continentals were made (same factory but not the same internals annoyingly). I accertained that is was either the tin can transistor up top or one of the 4 Silicone transistors. Through trial an error I established it's one of the MTJ00109 type. Online organ guides have the replacement for this as 2N5449 (NPN) which I actually had 3 of already. Those went in and the problem persisted, but got slightly better.
Not having any more to hand I stole one from the adjacent cards and that fixed part, but not all of it
So, currently, the E card has it's 3 originals put back in it, plus the one from the F card...and now it works great. But not the F
I managed to rummage around and the only other NPN I had was this big ol' 40w thing that I wedged into it for the time being. It works, but it's not quite right. You can see it on the right hand side with it's little heatsink thing poking out like a plumbers asscrack Further reading showed that BC549 transistors are a suitable fit, so I ordered 100 for £5 delivered. Lets see if those get me any closer!
Once that's fixed and I'm happy with that I'll turn my attention to giving it a proper recap, and take a look at the vibrato circuit as it has an underlying noise in it that's unaffected by volume (likely some cap noise).
Fun times.
