[R-390] Gain drift

[Roy Morgan]

> On Oct 16, 2018, at 2:54 PM, dog <agfa at hughes.net <mailto:agfa at hughes.net>> wrote:
> 
> ... I've got some tube extensions so I can put signals into each stage as I go along,

The RF deck has a number of test points - often at the grid of a stage.  Little test prod jacks on the chassis among the tubes. 

> ... I'm going to have to be sure I put the signal either through some small capacitor

Yes do that - there may well be AGC voltage at those test points.  The capacitor (100 PF maybe ?) will keep the signal generator output from “shorting” the AGC voltage.  There are tables of expected RF voltage at these different test points for “standard output” from the audio stage. (Gains all the way up, I would assume.)

If you are fussy about it, arrange a load on the generator output (likely 50 ohms) so as to give more or less correct indication of output voltage from the signal generator. 

> ... I tried some of the E ports casually, but that didn't seem very effective.

Not sure what you mean by E ports -  maybe these test points I am referring to.

Roy

Roy Morgan
k1lky68 at gmail.com <mailto:k1lky68 at gmail.com>