Lots of good on what I was looking for. I have done the neutralization
the way it is outlined in the manual and think I have it pretty good.
This T4 was a rust bucket basket case when I got it and it had several
burned up cathode resistors, two in the Driver cathode cicuit alone and
one in the plate circuit of the driver. I replaced those and began the
neutralization per the manual. As I moved the neutralization cap all of
a sudden the radio started sparking and smoking. The same 3 resistors
had burned up. So I am thinking that some kind of wild oscillation is
taking place when I hit a certain spot on the neutralization cap. So I
replace the resistors again. And the very same thing happens again. So
I look at the charred mess and the black smoke deposits in the radio and
try one more time. This time I replace the resistors and remove the
neutralization cap and find that at a certain rotation of the cap the
plates short together. So what was happening was that I was getting HV
from the PA tubes into the plate circuit of the 12by7 driver. No wonder
those resistors cooked. I Put it all back together and find that I can
get no output at all now. It turns out that the filaments of several of
the tubes along with the #47 pilot lamps had all burned out. So I
replace those tubes and lamps but still no output. I replace one more
tube in the Tx chain and she comes back to life.
She really has been abused but is putting out respectable power now and
is neutralized to a pretty good extent. Now I want to try the
neutralization scheme which removes the HV and Screen voltages. I will
be careful... I have learned the hardway before at least once or twice.
Steve NU0P
On 10/23/2012 20:17, Steve wrote:
I have a Drake T4 that needs neutralization . I have tried the
approach given in the manual and while it seems to work I thought I
might use this as an opportunity to learn how to do what is called a
Cold Tube neutralization where you do not apply High Voltage to the
plate. Seems that you can Neutralize the tube with only filament
voltage, bias and screen voltages applied. Has anyone done this and
if so what is the preferred method of doing it.
Steve NU0P
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