[ARC5] T-19 Update

[Kenneth G. Gordon]

On 17 Dec 2012 at 18:00, Mark K3MSB wrote:

> I did test all tubes on my Hickock and they tested OK (but of course
> that really doesn't stress PA tubes).

Correct. The only real test of a tube is substitution of a known good one.
 
> I'm using a Heathkit IM-11 VTVM for measurements via a small alligator
> clip.  I'm only measuring one item at a time.

That will still only measure DC or low frequency AC. At DC, its input 
"resistance" is 11 megohms. At AC it is much lower and will still load the 
circuit you are testing.

If you don't have one, get a Heathkit "Demodulator Probe", or an "RF Probe" 
for your IM-11. I can give you model numbers if you need them. I have seen 
those regularly on eBay for very little money, and for the sort of measuring 
you are doing, they are priceless.

> I checked all resistances as per the schematic before power up and all
> resistors were within tolerance (which, I must confess, surprised me).

Most of us are probably not too surprised by that. However, I think most of us 
WOULD be surprised if all the fixed-capacitors are still OK...especially that 
can-type in the back.
 
> I provided measurements without drive just for some additional data
> points.

Never, ever do that. There are far safer, and more accurate, ways to obtain 
sufficient data.

As Niel pointed out, without drive, the grid bias is next to nothing, and the 
tube will draw as much plate current as your power supply can provide.

This is, most definitely, NOT A GOOD THING!


Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   Wayne