For a 7A26, with 20,000 times input resistance (if it was purely
resistive), and
2/5 the bandwidth, the thermal noise would be 1.8mV which would be so
great you couldn't help but notice it on the most sensitive scale because
it
would occupy more than 1/3 division of the CRT. So why don't you see it?
On full bandwidth in my 7904 workhorse, one of my 7A26's on DC coupling
measures 1/3 of a *minor* division at 5mV/div (needed a magnifying glass for
that) - so about 0.1mV tangential noise, and it looks just like fuzzy noise.
With the 20MHz bandwidth limit switched in the trace is so narrow it is
impossible to measure the noise.
Craig
