Re: Of transistor amplifiers and CRTs...

Philip Pemberton wrote:

>
> Pooh Bear wrote:
>> Philip Pemberton wrote:
>>
>> > "Don't even THINK of calculating bias resistors based on the Hfe of a
>> > transistor, because it varies depending on A LOT of factors", but then
>> > says nothing about how you should design it...
>>
>> Simply design as if hfe was much lower. That way, the influence of bias
>> current will be minimal.
>>
>> Graham
>
> It looks like the big problem I've got is that the voltage input spans
> a range of 0V to 4V relative to ground, while the transistor ("Q")
> emitter is going to be about 500V below ground. Putting a capacitor
> between Q.base and Vin and adding a resistor between Q.base and
> Q.emitter should get rid of the "offset", but if the signal goes DC
> (which is quite likely) then the beam will turn off.
> An opamp would be one way to deal with the offset, but I expect opamps
> that can handle 600V are few and far between (not to mention
> expensive).
>
> Later,
> Phil.

I don't quite understand what you are asking for: What voltages do you need
on the CRT electrode when the beam is on, and what voltage do you need when
the beam is off? If you could post a drawing of the circuit on a website
somewhere then that would be helpful too.

Chris

.

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