Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: PRR on April 29, 2010, 11:57:08 pm
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So my neighbor is cleaning out somebody's barn, taking scrap-iron to the recycler. He asks me if I know anything about electronics, he's got some things with knobs and screens.
I find about two pickup-truck loads of "gear" dumped in the mud in the rain. Much of it is microwave stuff, bolometers; more is video, phasemeters. There's a company tag, they did leading-edge video surveillance from the 1960s to now. All this stuff is very 1960s. Much of it has had parts gently removed: I'm sure that into the 1980s they kept these boxes as spare-part donors for other boxes still in service. I gather an employee took this stuff, retired, and stored it in his barn until he realized he was never going to do anything with it. Then my neighbor scooped it onto his truck and dumped it for scrap-sorting.
Of that near-ton of stuff, about to be sold for pennies a pound, all I could find worth snagging was a Simpson meter full of green yuck, and an H-P 120B 'scope.
I dry it out, wipe some dirt off. Hmmmm, look at that big hole in the top, like it was stabbed by a small fork-lift. And I'm turning it around and around.... where do you plug it in?
I get the manual, and an old lamp-cord, and hay-wire it.
It works. It shows 60Hz finger-buzz, it shows the internal (neon-lamp!) calibrator, and the calibration seems better than 5%. Brightness is ample and focus is fine.
There's enough vertical shift when V.Gain is turned to tell me something isn't as perfect as it was in 1991 (the last calibration sticker). But so close that it may cook-out (reform the main caps, getter the input tube, dry the mud). Switches glitchy, but I've had worse.
Way-cool pot-metal die-cast bezel around the screen, like something from a 1957 Imperial.
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He asks me if I know anything about electronics,
heh ...understatement of the year.
all I could find worth snagging was a Simpson meter full of green yuck, and an H-P 120B 'scope.
Very nice find. That'll look good in the "lab".
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Not just look good.... my thesis is that a low-feature 450KC (0.45MHz) 'scope like this is all you need to work on guitar amps.
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Nice find! :smiley:
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He asks me if I know anything about electronics
He hadn't noticed the two Tesla towers in the backyard?
:smiley:
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nice score! :smiley:
no inputs on the banana connectors - how is it displaying a sq wave in your pic?
that is a nice clean trace...
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Nice dumpster score! BAMA has a manual here: http://bama.edebris.com/manuals/hp/120b/
:occasion14:
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> how is it displaying a sq wave in your pic?
"...it shows the internal (neon-lamp!) calibrator"
> that is a nice clean trace...
Actually it is "poor". Remember the recent "Noob" thread "...is it normal for the the square wave in a analog scope not to have any vertical lines in the trace?" The rise/fall lines are clearly visible on this 'scope's calibration signal, because they come from neon-lamps with gas-ion speed issues.
No matter. This cal source is not even rated for frequency, nor is the 'scope intended for BNC X10 probe alignment. You want to see 6 divisions top to bottom, and mine is very very close.
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Nice find! I had one of those, in just that version. It's all you need for audio. I'm not so sure how good it'll be for DC voltage measurements because of the homebrew probes, but the price can't be griped at!