Re: 547 Recap
I can't help you with some of these things, but perhaps I can tell you what you're doing in some of this.toggle quoted messageShow quoted text
The deflection plates of a CRT should (for various reasons) be driven in push pull. That is, if you have a signal at the input of the amplifier, it should produce two signals, one going plus, one going minus. This gives you effectively twice the sensitivity of the case where you hold one plate fixed, and feed a signal to the other.
Somewhere in the horizontal or vertical amplifier chain, you have a single signal. There's a circuit that produces a positive going and a negative going signal from one signal. The vertical or horizontal amplifier amplifies each signal and drives each plate from that resultant signal. You have one chain doing a positive signal, one doing a negative signal.
If you were to short the deflection plates of the CRT, then if the geometry is right, the spot ought to be in the middle (either H or V) depending on what you shorted.
A useful technique is to go from the plates back and short the equivalent signal - to +. If you don't get a display where the dot is exactly in the middle, then the amplifier is not giving you the same signal + and -, and you may have a bad component.
Anything you get where the signal is synchronous to the line generally indicates either ac line leakage to the amplifier, or bad power supply ripple.
Shorting two transistors' collectors in this differential amplifier doesn't really increase the load, it just makes the + and - channel signals identical.
Proper working of a scope says that not only are the power supply voltages within tolerance, but the ripple is, as well.
Nasty things happen with ripple.
On 5/9/2021 7:42 PM, J via groups.io wrote:
I have a 547 that I'm thinking about recapping. But I have a few questions before I start working on this, as I was having trouble finding info in the search function on the website.