[ARC5] T-19 Update

[Kenneth G. Gordon]

On 16 Dec 2012 at 21:42, Mark K3MSB wrote:

> As posted earlier this year I´m working on my first T-19 project.
> 
> I started testing it this week, but there are a few issues that I´m
> stumbling with.
> 
> Here are my voltage measurements:
> 
> Oscillator Voltage OFF

Huh? Why did you do this?

>           Key Up   Key Dwn
> 
> Plates:   550       440

Plate CURRENT is probably 300 mA....not good.

> Screens:  550       275
> Grids:      0       -18 DC
>             0       0.1 AC
> 
> Oscillator Voltage ON
> 
>           Key Up   Key Dwn
> 
> Plates:   550       510
> Screens:  550       150
> Grids:      0       -40 DC
>             2.1      2  AC
> 
> As you can see, the screen voltage is about 100V too low under key
> down conditions.

This indicates that the tubes may be gassy due to someone running them 
too hard. The screens are pulling too much current. They are pulling enough 
current to drop 400 volts across the 20K screen dropping resistor, or 20 mA, 
which is a tad high. Also, your plate current is obviously very low.

Try a new pair of 1625s.

Also, it looks like your grid voltage is too low. It should be about -80 VDC. 
Grid current should be about no more than 3.5 mA per tube, or 7 mA for the 
pair.

It sounds to me as though your 1626 oscillator tube is weak or not working 
properly also.

Ken W7EKB