Knight T-150 Ham Radio Transmitter, R33 \"blown\" apart...

[server]

Hi,

A \"Ham\" radio friend has an old Knight T-150 transmitter. \"R33\" , 150
ohm 20W, blew apart due to overload. This resistor is in the +800V circuit,
which is the Plate voltage for the Output tubes (6146). He replaced that
resistor. I told him to remove those Output tubes and measure the plate
voltage. When the transmitter was in \"Standby\" mode, the voltage was
+800V. However, when he switched the Function switch out of Standby,
the voltage dropped a lot and he heard a humming sound.

Does anyone have an idea what is loading down the +800V
(Output tubes removed)?

Thank You in advance, John N3AOF

 

[Peter W.]

Given the age of that device, I have to suspect a leaky cap somewhere. Has it been recapped? There are large number of small-value caps-to-ground starting with 6-46, 47, & 48 (dual-section) that I would start with being as they are electrolytic. But if it has not been recapped, do them all.

Peter Wieck
Melrose Park, PA

 

[Sjouke Burry]

On 14.11.20 21:04, Peter W. wrote:

Given the age of that device, I have to suspect a leaky cap somewhere. Has it been recapped? There are large number of small-value caps-to-ground starting with 6-46, 47, & 48 (dual-section) that I would start with being as they are electrolytic. But if it has not been recapped, do them all.

Peter Wieck
Melrose Park, PA

Also, if some cap is consuming that much, it must heat up
rather fast, and show where the problem is.