On Tue, Apr 6, 2021 at 02:01 AM, Dave Peterson wrote:
So why the discrepancy with early, yet changed, service manual documentation?
What's the history of the Post Accelerator Grid? When was it introduced?
Hi Dave,
The expansion mesh is a type of electric lens in a CRT that provides increased deflection sensitivity. It had been used in several 7000-series CRT's predating the 465.
I have several reasons to be convinced that the 465 used an expansion mesh from the beginning:
1. Its influence on the design, features, and functioning of the 'scope is such that it would be part of the original design brief, not something that would easily be added in a later version of the same model. It takes its place as one of the anodes in the CRT and it's dome-shaped, hollow side toward the tube socket.
2. The voltages on CRT pin 12 in the sub-250k S/N's and those above 250k are quite comparable, both being -150V nominally.
Looking at the SMs, I see a sub-250k version (your version 070-1330-00, with M20, 159/573 change sheets), where one of the main changes is the substitution of a discrete vertical amplifier, replacing the IC-version. That had to be done because of a shortage of vertical output IC's.
According to the base version SM, a CRT 154-0676-00 was used up to S/N B010499 (B010100 often was the lowest Beaverton S/N), which was followed by 154-0676-05, starting from S/N B010500.
The first print 250k+ SM (070-1861-00, august '74) mentions CRT model 154-0676-10 from S/N 250k and 154-0731-00 from S/N B274371. The latter model probably produces a sharper picture. It was also used in the 465B successor to the 465.
This brings me to
3. It would have been quite unusual for Tek to use the same main model designation (154-0676) both for a meshless version and a version with an expansion mesh. Differences in mesh construction and layout are thinkable though.
Raymond
Raymond Domp Frank