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Neon Bulbs in Tube Circuits


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5/2/2000 3:29 PM
Andrew M.
Neon Bulbs in Tube Circuits
A friend of mine picked up an all tube Lowry organ at a thrift store. Opening it up I see it has about quite a few neon bulbs scattered around the circuit. Anyone know what purpose they might serve?  
 
Andrew.
 
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5/2/2000 3:48 PM
Preben Hansen
I think they are part of the oscillators for the "tones".  
Preben
 
5/2/2000 7:18 PM
Jethro Tull Bodine

May have been used as limiters along the circuit path.. some Hammonds used a bulb as a limiter on the input of the reverb unit.. as some derived the signal from the Main console speaker.. kinda like those old electro-harmonix "golden throat" talk boxes...used a 1156 tail light bulb..same idea  
Jethro
 
5/2/2000 8:19 PM
R.G.
Preben is correct - they're part of the tone generators. Specifically, they're the octave dividers that generate octaves down from the highest tones in the box. There's a very old trick for making a divide-by-two flipflop from two neons.  
 
They're not limiters - neons are negative resistance devices. Filament bulbs are positive resistance, and more importantly postive *coefficient of resistance* devices, which makes them well suited to limiters and compressors.
 
5/3/2000 6:02 AM
Jethro Tull Bodine

Cool RG... that was a way they used to get *around* so to speak, the Hammond type circuits?  
That is all I'm familiar with.
 
5/4/2000 12:48 AM
pumpstein
Pumpstein's PreAmp Proto-Palace???
Is that the Lowrey with the huge copper chassis and all the 6X8 tubes? Has the 7591 output tubes? 2x12" alnicos?  
 
I picked one of these up a few weeks ago, also at a thrift shop, and after I robbed all the neat stuff, it occurred to me that the chassis would make a very cool breadboard setup for experimenting. All those tube holes, a copper chassis and the power amp already setup might make for a nice pre-amp proto-palace.  
 
plus: it has the hinges already mounted on it, so you can just pop it on a board and flip it up when you need to solder.  
 
An elder organ tech friend of mine who has been in the biz for like 50 years told me that he used to go nuts trying to find decent 6X8's...something about them never having been mfg'd well...I guess Lowrey kind of bought the farm there...  
 
...interesting: when I mentioned that the 7591's were hard to come by, and that they were widely regarded as nice-sounding, reliable tubes, he scratched his head for a sec, then said, "You know, now that I think of it, when I was an authorized Lowrey tech, I never replaced a single pair of those 7591's...I kept expecting to have to, but they just never went bad."  
 
I love tube organs. They are the organ-donors of the donor organ world. (someone stop me before I pun again)  
 
- P
 
5/4/2000 4:28 AM
ADM

The organ belongs to a friend of mine, I've just had a quick look at it, it has a pair of 7591 output tubes and a built-in Leslie speaker. It actually sound pretty good. It is actually really clean sounding, my friend is hoping to get a slightly more overdriven sound. I'm not sure what's the best way to go about that, overdrive a preamp stage, or mess with the bias. I can't imagine assembling one of those things though is such a rat's nest of wiring. They must have been pretty expensive in their day.  
 
Andrew.
 

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