The old stories do really make me wonder whether the
techy just pull the component and switch it around
without calculating the new configuration. I am VERY
tempted to do that all the time BUT must resist!
Calculation is not exact but the approximation is
pretty close.


John Chung


--- "Alan B. Pearce" <A.B.Pearce@rl.ac.uk> wrote:

> >Of course, this was back in the days when 4MHz was
> 'fast' for
> >a system clock speed, and the FCC regulations on
> unintentional
> >emitters were in their infancy or earlier, so you
> weren't
> >expected to run into too many "real world" issues
> with "wire"
> >unless you were building radio-like things.
> 
> A friend of my fathers used to tell how he got roped
> in to sort out peoples 
> home project valve amplifiers. One he mentioned
> would have one output tube 
> have the anode glowing a dull red, and over a few
> seconds that one would 
> fade, and the other tube of the push-pull pair would
> increase in colour. 
> Moving the grid stopper resistors from the tag board
> to the valve sockets, 
> with very short wires cured that one.
> 
> The people he helped would mutter about how after he
> had finished, the 
> amplifier was built like a radio transmitter ...
> 
> Same friend built himself a tape recorder, when such
> things were few and far 
> between, and definitely not found in homes (he
> worked for a state 
> broadcasting organisation at the time IIRC). Had the
> bias oscillator working 
> nicely, at the correct frequency somewhere around
> 50kHz - until he went into 
> record mode and connected the erase head to the
> oscillator, at which point 
> it oscillated at somewhere around 400MHz. Problem
> turned out to be length of 
> wire between the valve and the bias oscillator tuned
> circuit. The tuned 
> circuit drastically dropped in Q when the erase head
> loaded it, and the 
> wires became a nice high Q transmission line at
> 400MHz. Cure was to move the 
> oscillator tuning capacitor to the other end of the
> wires by putting it on 
> the valve socket. 
> 
> -- 
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