Re: Where is Graham's mixer design? (was Re: RAT Tube Mixer update?)

In article <fqf4uh$tam$1@[EMAIL PROTECTED]
>,
 Ian Thompson-Bell <ruffrecords@[EMAIL PROTECTED]
> wrote:

> Eeyore wrote:
> > 
> > Ian Thompson-Bell wrote:
> > 
> >> Has anyone thought of using a grounded grid amplifier as a mix amp?
> > 
> > No point as far as I can see.
> > 
> > Graham
> > 
> 
> I can think of several.
> 
> 1. Only needs one triode
> 2. Input/output transfer characteristic is very linear when used with 
> current source inputs
> 3. No Miller effect.
> 4. Input impedance approx 1/gm

Are you sure about that?  By my calculation that approximation only 
holds as long as Ra is small compared with the load resistor.  Perhaps I 
made a mistake in my hand done calculations and should try to look the 
result up in the RDH4th?

> 5. Gain approx anode load resistor over input resistor

Doesn't that gain approximation assume that Ra is low compared with the 
value of the load resistor?

There seems to be a serious compromise here with respect to achieving a 
low input resistance while maintaining the gain close to unity!

> Disadvantages are:
> 
> 1.Heater cathode leakage can inject hum/noise into input path.

Is this a serious problem assuming a DC heater supply is used, and the 
heater bus is well filtered/isolated to prevent the entry of other noise 
sources?


Regards,

John Byrns

-- 
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