VALIANT LOW VOLTAGE XFORMER

[n6biz]

VALIANT LV XFORMER GETTING TO WARM ... ACTUALLY HOT...
WHAT SHOULD I CHANGE OUT ...
AND DOES ANYONE KNOW OF SOMEONE SELLING A COMPLTE RECAP KIT FOR THE VALIANT?
AND GOING SOLID STATE FOR THE RECTIFIERS...
WHAT DO U DO?
73...

[Pete, WA2CWA]

I wouldn't "change out" anything until I determined what is the problem. Obviously, if all the filter caps are original, they should all be changed out. Check all the tubes with a good tube tester. Check the voltages and resistances using Tables 1, 2, and 3. Just ad hoc changing out components can lead to other problems unless you know and understand if there really is a problem.

[WQ9E]

In addition to what Pete advised:

If you have an early Valiant, make certain that the leads from the LV transformer to the 866A filamentary cathodes are using wire rated for high voltage.  Early Valiants were built with standard hookup wire here and it will short to chassis and each other taking out the LV transformer.

I don't like MV rectifiers so I replaced the high voltage rectifiers in all of my Valiant transmitters but switching the B+ rectifier to SS will generally make the transformer run hotter, especially if you don't add proper voltage dropping resistors.  The LV transformer is nowhere near overloaded in a properly operating Valiant.

The LV transformer is protected by a separate fuse, if the proper value installed here?  If the transformer is getting very hot very quickly I would disconnect all secondary loads and give it another test.  IF it still heats up rapidly then it has one or more shorted turns and only a rewinding will make it right again.

[AB2EZ]

I addition to what Pete advised (and also Rodger... who posted just before I pushed my "post" button):

Step 1. Turn off the transmitter, un-plug it, and let everything cool down.

Step 2. Remove both the low voltage rectifier tube (V20: 5V4) and the bias rectifier tube (V21: 6BY5 if I'm reading the somewhat blurry BAMA schematic correctly). This will remove all the loads (except filaments) on the transformer (as Rodger suggested)... including the electrolytic filter capacitors associated with both power supplies.

Step 3. Remove both HV rectifier tubes (so that the HV won't be applied to the circuitry in the transmitter in the absence of the low voltage B+ and the bias voltages). Make sure the two disconnected plate caps are insulated with electrical tape.... so that they won't make electrical contact with the chassis, etc.

Step 4.  Turn the transmitter back on.  Does the low voltage transformer still get warm/hot?

Post the result of steps 1-4 for further steps.

Stu

[AB2EZ]

As a post script:

The low voltage transformer supplies a lot of filament power (even more if the AC line voltage is above 115VAC):

Five 6146's: 40 watts
Two 866's: 25 watts
One 5V4: 10 watts
One 6BY5: 10 watts
One 6AQ5: 2.8 watts
One 6CL6: 4 watts
One 5763: 4.7W
Two 12AU7: 3.8 watts
One 12AX7: 1.9 watts
One 6AU6: 1.9 watts
One 6AL5: 1.9 watts
One 6C4: 1 watt

Plus indicator lamps

For a total of 110 watts of filament power

With the LV, bias, and HV rectifier tubes unplugged, there is still 65 watts of filament power provided by this transformer.

Separately... although I haven't done the analysis, my guess is that the total current normally being drawn from the +300V (low voltage) supply is in the ballpark of 100mA. 300V x 0.1A = 30W. Likewise, the bias supply is delivering about 20mA of current. 275V x .02A = 5.5W. Therefore, the DC power normally being provided by the low voltage transformer is less than 33% of the total of the DC power and the filament power that the LV transformer is normally providing.

If the transformer runs cool with the rectifier tubes unplugged, it will be interesting to see how plugging them back in (not all at once) affects the transformer's heating.

Stu  

[n6biz]

TU EVERYONE FOR UR REPLYS ...
WE WILL TAKE OUT THE TUBES FIRST...
73...