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    Neon Safety Lamps on Grids?

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    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Neon Safety Lamps on Grids?

    Post by sKiZo on Sat Jun 08, 2013 12:33 am

    I was just reading a killer article on the Marantz 10B in Vacuum Tube Valley (Issue 5-1996), and they mentioned using neon safety lamps to protect the tube filaments during power up.

    "We used an idea we got from Tektronix oscilloscopes on the model 9 amp and 10B tuner - neon safety lamps, to protect the tubes at turn-on in the direct coupled audio stages. It kept the grids from going too far positive before the filaments come up - you could have a few hundred volts on the grids! It would arc internally, but the neons come on at 70-80 volts and protect the grids. It only adds a few picofarads of capacity to the circuit. It's a great, cheap way to protect circuitry that's direct coupled. A lot of other companies should be using it."

    Anything in our stuff that could benefit? Anybody tried it?



    * Did some more digging, and it looks like the NE-2 "glow" lamp is used a lot in this application - couple bucks a pop for NOS. New at Mouser for 30 cents. They're also supposed to be dead quiet in circuit. There's also an NE-3 long life variant available.

    Here's the schematic if anyone want's to take a peek at how they did it ... I'd think it'd just be hooked in parallel on the B+? They're rated 65vac so they'd need to be stepped down? Something for one of the design gurus here ...

    http://911manuals.com/preview/Marantz/10-B-D-EN2-930-MAR.png

    arledgsc

    Posts : 330
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Neon Safety Lamps on Grids?

    Post by arledgsc on Sun Jun 09, 2013 12:24 pm

    Holy cow! That Marantz preamp schematic is probably the most complicated audio tube design I have ever witnessed. Interesting but not convinced that we would have that situation in a Dynaco type amp. Maybe with solid state rectifier, no relay board, no standby switch, etc.

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Neon Safety Lamps on Grids?

    Post by sKiZo on Sun Jun 09, 2013 2:51 pm

    The complexity could explain why it was pretty much the best ever built. No corners cut - show me another one with eight IF stages ... the tuner is a work of art. wOw.

    Maybe with solid state rectifier, no relay board, no standby switch, etc.

    That was kind of the point. Seems to describe the ST-120 anyway. I'd think the bulb accomplishes the same thing as a CL-90 inrush limiter in that it would damp any surge on start up, but ... not really up on it.

    Speaking of stand by switches ... anybody play with that on these rigs? I put one on a ham rig or two, but that wss because they'd take forever to stabilize otherwise. Just turn the heaters on, let it sit an hour or so, and frequency wouldn't be wandering all over the dial when you started talking.

    GP49

    Posts : 717
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Neon Safety Lamps on Grids?

    Post by GP49 on Mon Jun 10, 2013 11:23 am

    arledgsc wrote:Holy cow! That Marantz preamp schematic is probably the most complicated audio tube design I have ever witnessed...
    Just to clarify, the Marantz 10B was an FM tuner. It was the finest ever built and far more complicated than any other; but ANY FM tuner will be more complicated than a preamp.

    Except, perhaps, the infamous Granco FM tuner, probably the WORST ever built.


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