Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: jjasilli on July 12, 2010, 08:51:35 pm
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After lying fallow for about 6 months I read up on the manuals, etc. and seemed to do OK with the online 'scope simulator. So I returned to the real thing, Protek 20mHz analog scope, bought used:
DC: VOM reads battery @ 9.45VDC. Scope probe set to 1X. Vertical Control set to 1. Scope reads 2.2 Graticule lines. That seems to be off by ~75%. Que passa?
AC: I can't vouch for the accuracy my vintage tube signal generator, but: Signal generator set to 500Hz; VOM reads 3.1VAC off the generator. Scope probe @1X. Vertical: dial @ 0.5 reads only 2.2 graticule lines; Horizontal dial @ .2 yileds 3 graticules = .6mS the reciprocal of which is 1667Hz. Horizontal @ .5 yileds 1.2 graticules = .6mS the reciprocal of which is 1667Hz. Finally something matches; but it's supposed to be 500Hz, not 1667Hz. Que passa?
Thanks!
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The Vert and Horiz variable knobs are set to the CLICK?
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Also, are you measuring the time of the AC waveform for a complete cycle, ie, positive and negative half cycles?
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The Vert and Horiz variable knobs are set to the CLICK?
Yes, and the inner, concentric adjustment pots are fully CCW.
Also, are you measuring the time of the AC waveform for a complete cycle, ie, positive and negative half cycles?
Yes.
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Yes, and the inner, concentric adjustment pots are fully CCW.
The detent/calibrated position for VARIABLE VOLTS/DIV is max CW, not max CCW. Turn the knob CW until you hear/feel it click in the detent. This may be very slight but you will be maxed out. The same goes for the VARIABLE TIME/DIV pot.
Refer to page 5 of the linked manual...
http://www.protektest.com/ProdManual/Man_P3502C.pdf
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BINGO! Full CW cal pot rotation works.
Vertical: DC is dead on. AC: With the inner pot maxed (I can feel the detent) the scope is reading ~5VAC; the VOM reads 4VAC off the signal generator. I assume this has to do with RMS or peak-to-peak stuff. Horizontal: dead on at 500Hz!!!
Thanks much! I promised myself I would learn to work this thing before any more amp projects.
(In my defence re the pot settings, the online tutorial 'scope required setting the pots fully CCW, so I did that with my 'scope. So you see I had absolutley no reason whatsoever to consult my Manual first. :angel )
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> the online tutorial 'scope required setting the pots fully CCW
Every tool is different.
But most 'scope's Cal position "clicks", which is why I used the word CLICK. I thought you would find that CLICK, even if only for curiousity. Don't make Sluckey smack you with your manual.
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Don't make Sluckey smack you with your manual. :laugh:
It's amazing how you can miss the obvious when confused. Thanks again guys for all your patient help & support. The 'scope is now fun and useful. Next on my agenda: build a dummy load box; and a power tube cathode resistor box with a 500R rheostat and a set of switchable bypass caps.
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Very cool - keep us posted.