[Central-Electronics] Fw: 100-V Scope problem

[w7fe]

----- Original Message ----- 
From: w7fe 
To: Gordon 
Cc: Central_Electronics_Radio at yahoogroups.com 
Sent: Monday, September 09, 2013 11:01 AM
Subject: 100-V Scope problem


I don't recall seeing any posts or other references to CE having substituted a 2BP1 tube with an adapter cable at some point in production. I'd guess that a previous owner of your 100-V did this substitution. It seems possible that the 2BP1 would work OK as long as the adapter cable is correctly wired and the tube is operational.

At any rate, it seems to me that one of the CRT's vertical plates is not receiving the proper centering voltage and signal voltage, based on the following:

As I recall the operation of a CRT, its electron beam is centered on the screen by equal DC voltages on each opposing pair of beam deflection plates. When another voltage (in this case RF) is then applied to the vertical plates, the beam is deflected vertically in a manner proportional to its waveform. This produces a vertical line on the scope face, centered between the two plates due to the DC centering voltages. If only one of the plates is receiving these voltages, the beam would be deflected in only one direction and not returned by the opposing plate, thus driving the trace off the screen. 

A DVM check at the socket should reveal whether connections are made to the correct pins on the 2BP1. Hopefully the base diagrams for both CRT types are a available somewhere on the internet for your reference. We haven't addressed the horizontal beam deflection yet, but let's try to solve one thing at a time. It would, however, be well to check those connections as well.

Finding a 2RP1 and ditching the 2BP1 and adapter cable is certainly a logical alternative. It shouldn't be difficult to procure the tube. This may or may not fix the problem, but at least you'll have the correct tube in the rig.


73 de Stu, W7FE

P.S.  Sorry that I didn't add this response to the previous message thread. I seem to have inadvertently and permanently deleted your most recent message, but I think I recall most of what you wrote.