PROBLEM: T4XC DRAKE, NO PLATE CURRENT DIP
 

Can anybody shed some light on a problem I have with my Drake T4XC? I just
cannot dip the plate current. There is a very slight dip when the capacitor
is at maximum capacitance but not very much. Any help would be appreciated.
thanks,
mike

"mike ferraro" wrote in message
news:0L4bc.102351$cx5.24700@fed1read04...
Can anybody shed some light on a problem I have with my Drake T4XC? I just
cannot dip the plate current. There is a very slight dip when the
capacitor
is at maximum capacitance but not very much. Any help would be
appreciated.
thanks,
mike

Here's some general advice, in no particular order.

A. Assuming you're testing into a dummy load:

*. Test the dummy load with a noise bridge. It should show very little
reactance at any frequency it's rated for.
*. Test the dummy load by loading up a different transmitter.
*. Perform the OTA tests, below.

B. If you're testing OTA:

*. Check the antenna, its feed, and the tuner if present. Flex the feedline
and all connectors and listen for received noise. Be sure all connections
are solid.
*. Use a noise bridge to determine the antenna's resonant frequency, and
perform the test at that frequency.
*. Check the resistors in the parasitic suppressors on the final tubes. If
they're burnt, replace them and neutralize the finals at the _HIGHEST_
frequency you'll operate on.
*. Inspect the finals with a magnifying glass: look for shorts, see if the
plate is tilted over, etc.
*. Check screen bypass caps.

That's all I can think of before my second cup of coffee.

YMMV. If it breaks, you get to keep both pieces and I'm not responsible.

Bill

Bill:

Thanks for the info, dummy load is good...I will check the other items and
get back to you...

mike

"William Warren" wrote in message
news:cKdbc.59687$K91.146750@attbi_s02...
"mike ferraro" wrote in message
news:0L4bc.102351$cx5.24700@fed1read04...
Can anybody shed some light on a problem I have with my Drake T4XC? I
just
cannot dip the plate current. There is a very slight dip when the
capacitor
is at maximum capacitance but not very much. Any help would be
appreciated.
thanks,
mike

Here's some general advice, in no particular order.

A. Assuming you're testing into a dummy load:

*. Test the dummy load with a noise bridge. It should show very little
reactance at any frequency it's rated for.
*. Test the dummy load by loading up a different transmitter.
*. Perform the OTA tests, below.

B. If you're testing OTA:

*. Check the antenna, its feed, and the tuner if present. Flex the
feedline
and all connectors and listen for received noise. Be sure all connections
are solid.
*. Use a noise bridge to determine the antenna's resonant frequency, and
perform the test at that frequency.
*. Check the resistors in the parasitic suppressors on the final tubes. If
they're burnt, replace them and neutralize the finals at the _HIGHEST_
frequency you'll operate on.
*. Inspect the finals with a magnifying glass: look for shorts, see if the
plate is tilted over, etc.
*. Check screen bypass caps.

That's all I can think of before my second cup of coffee.

YMMV. If it breaks, you get to keep both pieces and I'm not responsible.

Bill

High VSWR, Sombody put in Toshiba finals ?

"mike ferraro" wrote in message
news:0L4bc.102351$cx5.24700@fed1read04...
Can anybody shed some light on a problem I have with my Drake T4XC? I just
cannot dip the plate current. There is a very slight dip when the
capacitor
is at maximum capacitance but not very much. Any help would be
appreciated.
thanks,
mike

Antenna not resonant. The tank circuit liked to see 50 to 75 ohm resistive.

Try reducing your 'LOAD' control.

Dan/W4NTI

"RP Jones" wrote in message
...
High VSWR, Sombody put in Toshiba finals ?

"mike ferraro" wrote in message
news:0L4bc.102351$cx5.24700@fed1read04...
Can anybody shed some light on a problem I have with my Drake T4XC? I
just
cannot dip the plate current. There is a very slight dip when the
capacitor
is at maximum capacitance but not very much. Any help would be
appreciated.
thanks,
mike

The problem was that one of the stator plates was shorting to one of the
rotor plates of the plate tuning capacitor. Plate current now dips just fine
at resonance. Thanks for the inputs.
mike