[Heathkit] IO-12 Vertical Drift

[Edward B Richards]

Yep! Replace the .1, or whatever they are, coupling caps. One or more is
leaking, changing the bias on the next stage.

73, Ed Richards K6UUZ
AMI member #1534


On Sun, 24 Apr 2005 16:43:45 -0400 "Harry Vaught, KT4AE"
<kt4ae at frozenlady.com> writes:
> I've got an IO-12 I built in the '60's that I'm trying to put back 
> into 
> general 'scope service.
> 
> The problem is that over a half-hour to forty-five minures, the 
> trace 
> will drift up to where you can't bring it back down to mid-screen.
> 
> I've replaced the 12AT7 and all the resistors and caps that would 
> seem 
> to have an effect on vertical position.  Nothing seemed to make any 
> difference.  Voltages are good - measurments after the trace drifts 
> don't show an imbalance.
> 
> The direction it faces on the bench also affects the trace position. 
> 
> Putting it right next to my SX-101A (a large hunk of steel), pulls 
> the 
> trace up about 1/4 inch.  This almost sounds like a floating ground, 
> but 
> I can't find anything.
> 
> Anyone run into anything like this?
> 
> Harry Vaught, KT4AE
> Maryville, Tennessee
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